COVID-19
A respiratory infection caused by SARS-CoV-2 that can range from an asymptomatic or mild illness to severe disease, Long COVID, and death.
What causes COVID-19?
COVID-19 is caused by SARS-CoV-2. It spreads mainly through infectious respiratory particles released when an infected person breathes, speaks, coughs, sneezes, sings, or exercises, especially during close contact or in poorly ventilated indoor spaces.
Symptoms and what to notice
Fever, chills, cough, sore throat, congestion, fatigue, headache, muscle aches, shortness of breath, nausea, vomiting, or diarrhea. Loss of taste or smell can occur but is less common with Omicron-lineage viruses.
How long can it last?
Symptoms often begin about 3 to 4 days after exposure with Omicron-lineage infections, although timing varies. Many acute illnesses improve within days to a few weeks, while Long COVID can cause symptoms or new health problems lasting at least 3 months.
How serious is COVID-19?
Older adults, immunocompromised people, pregnant people, and those with certain underlying conditions have higher risk of hospitalization, respiratory failure, blood clots, organ injury, and death. Children can rarely develop MIS-C.
Treatment and management
High-risk patients should seek treatment quickly. Paxlovid is an oral 5-day course that must start within 5 days of symptom onset and has important drug interactions. A 3-day intravenous Veklury (remdesivir) course can start within 7 days. Lagevrio (molnupiravir) is an alternative for certain adults when preferred options cannot be used.
Vaccine: who and when?
U.S. 2026-2027 products are Comirnaty, Spikevax, MNEXSPIKE, and Nuvaxovid, using mRNA or protein-subunit technology and targeting the JN.1-descendent XFG variant. CDC recommends a 2026-2027 dose for adults age 18 and older, for children with moderate or severe immunocompromise, and through shared clinical decision-making for other children. Product choice and dosing depend on age, risk, vaccination history, and current FDA labeling.
Cost note: Patient cost and access vary by product, insurance, age, eligibility, and provider. Coverage may be available through private insurance, Medicare, Medicaid, public-health safety-net programs, and the Vaccines for Children program.
Trusted source
Patient cost varies by insurance, provider, location, and eligibility. Coverage and public-health access differ, so listed prices are examples rather than guaranteed patient prices. This page is for general education and does not replace individualized medical advice, diagnosis, vaccination assessment, or treatment.
COVID-19: History, Symptoms, Transmission, Variants, Treatment, Prevention, and Vaccine Information
COVID-19, short for coronavirus disease 2019, is an infectious disease caused by the virus SARS-CoV-2, or severe acute respiratory syndrome coronavirus 2.
The disease first came to international attention after a cluster of unexplained pneumonia cases was reported in Wuhan, China, in December 2019. Within only a few months, the newly identified virus had spread around the world, producing the largest global pandemic in more than a century.
COVID-19 can range from an infection with no symptoms at all to a mild cold-like illness, pneumonia, respiratory failure, multi-organ disease, long-term health problems, and death.
Common symptoms include:
- Fever
- Cough
- Sore throat
- Runny or congested nose
- Fatigue
- Headache
- Muscle aches
- Shortness of breath
- Nausea
- Vomiting
- Diarrhea
Loss of taste or smell can occur, although these symptoms have become less common since Omicron-lineage viruses became dominant.
One of the most important characteristics of SARS-CoV-2 is its ability to change genetically. Successive variants have altered transmission patterns and immune protection, making reinfection possible and requiring vaccines to be periodically updated.
COVID-19 is no longer causing the extraordinary global emergency seen during the earliest years of the pandemic, but the virus has not disappeared.
In its August 2026 global risk assessment, the World Health Organization classified the worldwide public-health risk from COVID-19 as moderate. WHO reported more than 779 million confirmed cases and more than 7 million confirmed deaths worldwide by June 28, 2026, while emphasizing that actual infections and reinfections have been vastly more numerous than reported case counts.
COVID-19 also has an important chronic dimension. Some people develop Long COVID, in which symptoms or health problems continue or emerge months after the original infection.
Important: This article provides general educational information and does not replace individualized diagnosis, treatment, vaccination advice, or emergency medical care.
What Is COVID-19?
COVID-19 is the disease caused by SARS-CoV-2.
The virus belongs to the coronavirus family, a large group of enveloped RNA viruses capable of infecting humans and animals.
Several coronaviruses routinely cause mild respiratory illnesses resembling the common cold.
Others have caused serious outbreaks, including:
- SARS, caused by SARS-CoV
- MERS, caused by MERS-CoV
- COVID-19, caused by SARS-CoV-2
SARS-CoV-2 belongs to the species Severe acute respiratory syndrome-related coronavirus.
The International Committee on Taxonomy of Viruses officially named the virus severe acute respiratory syndrome coronavirus 2, abbreviated SARS-CoV-2, in February 2020. The disease itself was named COVID-19 by the World Health Organization.
COVID-19 Quick Facts
| Feature | Information |
|---|---|
| Disease | COVID-19 |
| Full name | Coronavirus disease 2019 |
| Virus | SARS-CoV-2 |
| Virus family | Coronaviridae |
| Genetic material | Single-stranded RNA |
| Main transmission | Infectious respiratory particles |
| Incubation period | Varies by variant, often around 3 to 4 days for Omicron-lineage infections |
| Disease severity | Asymptomatic to critical |
| Reinfection possible | Yes |
| Main diagnostic tests | NAAT/PCR and antigen tests |
| Antiviral treatment available | Yes |
| Major outpatient antiviral | Paxlovid |
| Other antiviral | Remdesivir |
| Long-term complication | Long COVID |
| Important pediatric complication | MIS-C |
| Vaccine available | Yes |
| Current U.S. vaccine types | mRNA and protein-based vaccines |
| Current status | Continuing global circulation |
The History of COVID-19
COVID-19 has an unusually well-documented history because the disease emerged during the era of genomic sequencing, global digital communication, international disease surveillance, and advanced molecular medicine.
In only a few weeks, scientists moved from reports of unexplained pneumonia to identification and sequencing of a completely new coronavirus.
Within one year, multiple vaccines were being administered.
At the same time, the pandemic caused enormous mortality, overwhelmed healthcare systems, interrupted education and employment, disrupted international travel, and profoundly affected societies around the world.
December 2019: Unexplained Pneumonia Appears in Wuhan
On December 31, 2019, the World Health Organization became aware of reports describing a cluster of pneumonia cases of unknown cause in Wuhan, Hubei Province, China.
The patients had an illness that could not initially be explained by known respiratory pathogens.
WHO requested additional information from Chinese authorities and activated its international incident-management mechanisms during the first days of January 2020.
January 2020: A Novel Coronavirus Is Identified
Chinese authorities identified a new coronavirus as the cause of the outbreak in early January 2020.
The virus was initially referred to as:
2019-nCoV
meaning 2019 novel coronavirus.
The viral genome was rapidly sequenced and shared, allowing laboratories around the world to begin developing molecular diagnostic tests.
WHO issued its first formal Disease Outbreak News report concerning the cluster on January 5, 2020.
Human-to-Human Transmission Becomes Clear
Early investigations increasingly demonstrated that SARS-CoV-2 could spread efficiently between people.
This ability distinguished the outbreak from an isolated animal-to-human event.
Transmission occurred through respiratory exposure, including before some infected people developed obvious symptoms.
That combination made containment extremely difficult.
January 20, 2020: First Confirmed U.S. Case
CDC reported the first laboratory-confirmed U.S. case on January 20, 2020 from samples obtained from a patient in Washington state.
CDC activated its Emergency Operations Center as the emerging outbreak expanded.
By January 30, the United States had documented person-to-person transmission.
January 30, 2020: WHO Declares an International Emergency
On January 30, 2020, WHO declared the outbreak a Public Health Emergency of International Concern, or PHEIC.
At that time, WHO reported 7,818 confirmed cases worldwide, most in China, with 82 confirmed cases across 18 countries outside China.
The declaration represented the highest level of international public-health alert available under the International Health Regulations.
February 2020: COVID-19 and SARS-CoV-2 Receive Their Names
On February 11, 2020, the disease was formally named:
COVID-19
The term means:
COrona VIrus Disease 2019
The virus itself was named SARS-CoV-2.
The disease name and virus name are therefore not interchangeable.
A person is infected with SARS-CoV-2 and may develop COVID-19.
March 11, 2020: COVID-19 Is Characterized as a Pandemic
Cases continued spreading internationally at extraordinary speed.
On March 11, 2020, WHO stated that COVID-19 could be characterized as a pandemic.
By this point, sustained transmission was occurring across multiple continents.
Countries introduced measures that included:
- Isolation
- Quarantine
- Travel restrictions
- School closures
- Workplace closures
- Masking
- Testing programs
- Contact tracing
- Limits on large gatherings
- Remote working
The severity of restrictions varied considerably between countries and over time.
What Is Known About the Origin of SARS-CoV-2?
The ultimate origin of SARS-CoV-2 has not been conclusively established.
WHO’s Scientific Advisory Group for the Origins of Novel Pathogens published an updated assessment in June 2025.
The group concluded that the weight of available scientific evidence supports zoonotic spillover, meaning transmission from animals to humans, either directly from bats or through an intermediate animal host.
However, WHO also stated that important information needed to fully evaluate all hypotheses remains unavailable and that alternative hypotheses, including an accidental laboratory-related event, cannot currently be completely excluded.
Therefore, statements claiming that the precise origin has been definitively proven go beyond the evidence currently available.
2020: Scientists Develop Treatments at Unprecedented Speed
Early in the pandemic, doctors had no proven antiviral medication specifically approved for COVID-19.
Researchers rapidly tested existing and experimental medicines.
Remdesivir became one of the earliest antiviral drugs shown to have clinical value.
The FDA issued emergency authorization for remdesivir in May 2020.
On October 22, 2020, the FDA approved remdesivir, marketed as Veklury, making it the first FDA-approved treatment for COVID-19.
Other treatment approaches were subsequently developed, including oral antivirals and therapies targeting the inflammatory complications of severe COVID-19.
December 2020: The First U.S. COVID-19 Vaccine Is Authorized
A major turning point occurred in December 2020.
The FDA issued an Emergency Use Authorization for the Pfizer-BioNTech COVID-19 vaccine on December 11, 2020 for people aged 16 years and older.
The pivotal randomized clinical trial involved approximately 44,000 participants and found very high protection against symptomatic COVID-19 during the period studied.
The Moderna COVID-19 vaccine followed shortly afterward.
Mass vaccination programs began across many countries.
August 2021: First Fully FDA-Approved COVID-19 Vaccine
On August 23, 2021, the FDA granted full approval to the Pfizer-BioNTech vaccine under the brand name Comirnaty.
It became the first COVID-19 vaccine to receive full FDA approval.
January 2022: Spikevax Is Approved
The FDA approved Moderna’s COVID-19 vaccine under the brand name Spikevax on January 31, 2022.
COVID-19 vaccination had by then become one of the largest vaccination campaigns in history.
2021: Alpha and Delta Variants Change the Pandemic
SARS-CoV-2 continued evolving.
Several genetically distinct variants appeared and spread internationally.
WHO introduced Greek-letter names for important variants so public communication would not rely on technical lineage codes or geographic labels.
Variants that became important during 2021 included:
- Alpha
- Beta
- Gamma
- Delta
Delta became particularly important because of its high transmissibility and its ability to cause large outbreaks.
November 2021: Omicron Emerges
On November 26, 2021, WHO classified the B.1.1.529 lineage as a Variant of Concern and gave it the name:
Omicron
The first known confirmed specimen associated with this lineage had been collected on November 9, 2021.
Omicron contained numerous mutations, particularly in its spike protein.
It spread internationally with extraordinary speed.
Over time, Omicron and its descendants displaced earlier variants.
The Omicron Era
Omicron did not remain a single unchanged virus.
It produced numerous sublineages, including descendants of:
- BA.1
- BA.2
- BA.4
- BA.5
- XBB
- BA.2.86
- JN.1
Later descendants continued evolving.
By the middle of the 2020s, global SARS-CoV-2 evolution was dominated largely by descendants of Omicron and particularly the JN.1 lineage.
WHO continues monitoring variant evolution because genetic changes can influence:
- Transmission
- Reinfection
- Immune escape
- Vaccine performance
- Diagnostic testing
- Antiviral effectiveness
- Disease severity
May 5, 2023: WHO Ends the COVID-19 Global Emergency
On May 5, 2023, WHO ended the COVID-19 Public Health Emergency of International Concern.
This did not mean that COVID-19 had disappeared.
It meant that the disease no longer met the criteria for the extraordinary emergency designation that had existed since January 2020.
SARS-CoV-2 continued circulating globally after the emergency designation ended.
COVID-19 in 2026
COVID-19 remains an active infectious disease.
WHO’s August 6, 2026 risk assessment stated that the global public-health risk remained moderate as of July 30, 2026.
The organization emphasized that SARS-CoV-2:
- Continues circulating globally
- Continues evolving
- Can still cause severe disease
- Can still cause deaths
- Remains particularly important for older and immunocompromised people
- Continues causing post-COVID conditions
WHO reported more than 779 million confirmed infections and 7 million confirmed deaths by June 28, 2026.
These figures substantially underestimate total infections because routine testing and case reporting have declined and reinfections are extremely common.
What Kind of Virus Is SARS-CoV-2?
SARS-CoV-2 is an enveloped, positive-sense, single-stranded RNA virus.
The virus contains several important structural proteins.
These include:
- Spike protein
- Membrane protein
- Envelope protein
- Nucleocapsid protein
The spike protein became particularly important because it allows the virus to attach to and enter human cells.
It is also the major antigen targeted by COVID-19 vaccines.
How Does SARS-CoV-2 Enter Human Cells?
The viral spike protein interacts with a cellular receptor known as:
ACE2
ACE2 is present on cells in several organs and tissues.
After binding and additional molecular processing, the virus can enter susceptible cells.
Its RNA is released.
The virus then uses cellular machinery to:
- Produce viral proteins
- Copy its RNA
- Assemble new virus particles
New particles leave infected cells and can infect additional cells.
Why Can COVID-19 Affect More Than the Lungs?
COVID-19 began as a respiratory disease, but scientists quickly learned that severe infection can affect multiple body systems.
Potentially affected organs include:
- Lungs
- Heart
- Blood vessels
- Brain
- Kidneys
- Liver
- Gastrointestinal tract
- Immune system
Some complications result directly or indirectly from viral infection, while others result from inflammatory, vascular, immune, or clotting abnormalities.
How Does COVID-19 Spread?
SARS-CoV-2 spreads mainly through infectious respiratory particles released when an infected person:
- Breathes
- Talks
- Coughs
- Sneezes
- Sings
Transmission risk is particularly important in shared indoor environments.
Factors that can increase transmission include:
- Poor ventilation
- Crowding
- Prolonged close contact
- High levels of virus in an infected person
- Activities involving heavy breathing or loud vocalization
Improving ventilation and air filtration can reduce concentrations of infectious respiratory particles indoors.
Can Someone Spread COVID-19 Before Symptoms Begin?
Yes.
People infected with SARS-CoV-2 can transmit the virus before developing symptoms.
Some infected people never develop noticeable symptoms but can still potentially transmit infection.
This characteristic contributed significantly to the difficulty of containing SARS-CoV-2 during the early pandemic.
Can COVID-19 Spread From Surfaces?
Surface transmission is possible in principle, but respiratory transmission is far more important.
Cleaning hands and frequently touched surfaces remains reasonable, particularly in healthcare environments, but COVID-19 prevention should not focus exclusively on disinfecting objects while ignoring ventilation, respiratory protection, vaccination, and avoiding close exposure when sick.
What Is the Incubation Period of COVID-19?
The incubation period is the time between infection and symptom onset.
It has changed somewhat as the virus evolved.
Early pandemic studies produced an average incubation period around 6.5 days.
During Delta circulation, approximately 4.3 days was reported in one major study.
During periods dominated by Omicron, studies found a median incubation period of approximately:
3 to 4 days
The incubation period for an individual infection can be shorter or longer.
What Are the Symptoms of COVID-19?
COVID-19 has an unusually broad range of symptoms.
Common symptoms include:
- Fever
- Chills
- Cough
- Sore throat
- Runny nose
- Nasal congestion
- Shortness of breath
- Fatigue
- Headache
- Muscle aches
- Body aches
- Loss of taste
- Loss of smell
- Nausea
- Vomiting
- Diarrhea
Symptoms alone usually cannot reliably distinguish COVID-19 from influenza, RSV, or other respiratory infections.
Is Loss of Smell Still a Common COVID-19 Symptom?
Loss of smell and taste became one of the best-known features of early COVID-19.
It still occurs.
However, CDC notes that these symptoms have become less common since Omicron-lineage viruses began circulating.
A person therefore should not assume they do not have COVID-19 simply because their smell and taste remain normal.
Can Someone Have COVID-19 Without Symptoms?
Yes.
SARS-CoV-2 infection can be:
- Asymptomatic
- Presymptomatic
- Mild
- Moderate
- Severe
- Critical
Some people test positive and never feel ill.
Others initially feel well and develop symptoms later.
Children are more likely than adults to remain asymptomatic.
What Does Mild COVID-19 Feel Like?
Mild disease may resemble:
- A common cold
- Mild influenza
- Sore throat
- Sinus congestion
- Mild bronchitis
People may experience:
- Runny nose
- Sore throat
- Headache
- Fatigue
- Cough
- Low-grade fever
- Body aches
A mild beginning does not guarantee that symptoms will remain mild, particularly in someone at increased risk for severe illness.
What Is Severe COVID-19?
Severe disease can involve substantial lung inflammation and impaired oxygen exchange.
Possible complications include:
- Viral pneumonia
- Low blood oxygen
- Acute respiratory distress syndrome
- Blood clots
- Cardiac complications
- Kidney injury
- Severe inflammatory disease
- Shock
- Multi-organ failure
Some patients require:
- Supplemental oxygen
- Intensive-care treatment
- Mechanical ventilation
- Other forms of organ support
What Is COVID-19 Pneumonia?
COVID-19 pneumonia occurs when SARS-CoV-2 infection causes inflammation within lung tissue.
Symptoms can include:
- Persistent cough
- Shortness of breath
- Fever
- Chest discomfort
- Low oxygen saturation
- Rapid breathing
- Severe fatigue
Chest X-rays or CT scans can show abnormalities, but CDC does not recommend using imaging alone to diagnose COVID-19.
What Is Acute Respiratory Distress Syndrome?
Acute respiratory distress syndrome, or ARDS, is severe lung injury in which inflammation and fluid interfere with oxygen transfer.
It was an important cause of death during the early stages of the COVID-19 pandemic.
Patients with severe ARDS may require mechanical ventilation and intensive-care support.
Can COVID-19 Cause Blood Clots?
Yes.
Severe COVID-19 can disturb normal clotting mechanisms and increase the risk of thrombotic complications.
These can include:
- Deep-vein thrombosis
- Pulmonary embolism
- Stroke
- Other vascular complications
This risk is especially relevant in hospitalized and critically ill patients.
Can COVID-19 Affect the Heart?
Yes.
Potential cardiac complications include:
- Myocardial injury
- Myocarditis
- Pericarditis
- Abnormal heart rhythms
- Heart failure
- Blood-clot-related cardiac complications
Some cardiovascular symptoms may also occur as part of Long COVID.
Can COVID-19 Affect the Brain?
Yes.
Neurological manifestations can include:
- Headache
- Loss of smell
- Cognitive difficulties
- Dizziness
- Confusion
- Stroke
- Seizures in severe illness
- Peripheral neurological symptoms
Post-infectious neurological symptoms can also occur.
Who Is Most Likely to Develop Severe COVID-19?
Age is the strongest overall risk factor.
Risk increases substantially with advancing age, particularly above 65 years.
Additional risk factors can include:
- Immune suppression
- Cancer
- Chronic lung disease
- Cardiovascular disease
- Diabetes
- Obesity
- Chronic kidney disease
- Certain neurological conditions
- Certain genetic or metabolic disorders
- Multiple underlying medical conditions
The number and severity of underlying conditions also influence overall risk.
Why Are Immunocompromised People at Greater Risk?
A weakened immune system may make it harder to control SARS-CoV-2.
Immunocompromised people may experience:
- Higher risk of hospitalization
- More severe disease
- Longer-lasting infection
- Lower immune response to vaccination
- Greater risk of death
Examples include some people with:
- Blood cancers
- Solid-organ cancers
- Organ transplantation
- Stem-cell transplantation
- Primary immune deficiencies
- Immunosuppressive medication use
COVID-19 and Pregnancy
Pregnancy increases the risk of severe illness from COVID-19.
Pregnant people who become infected can face increased risk of complications affecting themselves and their pregnancy.
CDC states that COVID-19 vaccination can reduce the risk of severe COVID-19 during pregnancy and has not been linked to increased health risks for pregnant people or their babies in available safety monitoring.
Treatment for COVID-19 should not automatically be withheld during pregnancy simply because a medication is being considered for a pregnant patient. Decisions should be individualized with appropriate medical guidance.
COVID-19 in Children
Most children with SARS-CoV-2 infection experience mild illness or no symptoms.
However, children can develop severe COVID-19.
Children at greater risk include those with:
- Medical complexity
- Congenital heart disease
- Obesity
- Diabetes
- Chronic lung disease
- Certain neurological conditions
- Immune suppression
Children can also develop a rare post-infectious complication known as MIS-C.
What Is MIS-C?
Multisystem inflammatory syndrome in children, or MIS-C, is a rare but serious inflammatory condition associated with SARS-CoV-2 infection.
It often begins weeks after the original infection.
Some affected children had few or no noticeable COVID-19 symptoms beforehand.
MIS-C can affect:
- Heart
- Lungs
- Kidneys
- Brain
- Skin
- Eyes
- Gastrointestinal tract
Common features include persistent fever plus symptoms such as:
- Abdominal pain
- Vomiting
- Diarrhea
- Rash
- Bloodshot eyes
- Dizziness
- Low blood pressure
MIS-C has become much less common than it was during the earliest pandemic years, but sporadic cases still occur.
What Is Long COVID?
Long COVID is one of the most important lasting health consequences of the pandemic.
CDC defines Long COVID as a chronic condition occurring after SARS-CoV-2 infection that is present for at least 3 months.
The condition may be:
- Continuous
- Relapsing
- Remitting
- Progressive
It can affect one or multiple organ systems.
What Are the Symptoms of Long COVID?
Long COVID can produce many different symptoms.
These may include:
- Severe fatigue
- Post-exertional worsening
- Shortness of breath
- Persistent cough
- Chest discomfort
- Heart palpitations
- Dizziness
- Headaches
- Sleep disturbance
- Loss or alteration of smell
- Loss or alteration of taste
- Memory problems
- Difficulty concentrating
- “Brain fog”
- Joint pain
- Muscle pain
- Digestive symptoms
- Changes in heart rate
- Exercise intolerance
Symptoms may improve and later return.
Some people recover within months.
Others experience problems lasting years.
Can Mild COVID-19 Cause Long COVID?
Yes.
Long COVID can occur after:
- Mild infection
- Severe infection
- Hospitalized infection
- Apparently asymptomatic infection
Anyone infected with SARS-CoV-2 can potentially develop Long COVID, including children.
However, the risk is not equal for every person.
How Common Is Long COVID?
Estimates vary according to:
- Study population
- Variant
- Vaccination status
- Definition used
- Follow-up duration
- Number of previous infections
WHO’s 2026 global risk assessment cited an estimate that approximately 6% of people with symptomatic COVID-19 develop post-COVID condition, with lower risk among vaccinated individuals.
Among those affected, approximately 15% were estimated to still have persistent symptoms at 12 months.
These are global estimates and should not be interpreted as a precise individual probability.
Is There a Test for Long COVID?
There is currently no single laboratory test that can prove that a particular symptom is caused by Long COVID.
Diagnosis generally involves:
- Previous SARS-CoV-2 infection or probable infection
- Symptom history
- Clinical examination
- Excluding alternative diagnoses
- Targeted testing based on symptoms
CDC notes that there are currently no approved tests that definitively establish whether ongoing symptoms are due to Long COVID.
Is There a Cure for Long COVID?
There is currently no single approved treatment that cures all Long COVID.
Care is individualized according to symptoms and affected organ systems.
Management may involve:
- Primary care
- Cardiology
- Pulmonology
- Neurology
- Rehabilitation
- Sleep medicine
- Mental-health support
- Physical or occupational therapy when appropriate
Certain patients with post-exertional symptom worsening require careful activity management rather than simply being told to exercise more.
Can Vaccination Reduce Long COVID Risk?
Current evidence indicates vaccination reduces the risk of severe acute COVID-19 and also appears to reduce the risk of Long COVID.
CDC describes vaccination as the best currently available tool for reducing Long COVID risk.
Can You Get COVID-19 More Than Once?
Yes.
Reinfection is common.
A person may develop COVID-19 more than once because:
- Immune protection decreases over time
- SARS-CoV-2 continues evolving
- New variants may partially escape existing antibodies
- Immunity from infection is not complete
- Immunity from vaccination is not complete
Reinfection can occur even after previous vaccination and previous COVID-19.
Do Vaccinated People Still Get COVID-19?
Yes.
COVID-19 vaccines do not create complete lifelong protection against infection.
Their major benefit is reducing the risk of:
- Severe disease
- Hospitalization
- Complications
- Death
Protection against infection also declines over time and can be affected by new variants.
This is one reason vaccine formulations are updated.
How Is COVID-19 Diagnosed?
Diagnosis is usually confirmed using a viral diagnostic test.
Two main categories are:
- Molecular tests, including PCR and other NAATs
- Antigen tests
CDC recommends viral testing rather than antibody testing to diagnose a current infection.
What Is a PCR Test?
PCR is a type of nucleic acid amplification test.
It detects viral genetic material.
PCR tests are generally more sensitive than rapid antigen tests.
They can detect relatively small quantities of SARS-CoV-2 RNA.
However, this sensitivity also means some people may continue testing positive by PCR for weeks after they are no longer in the early phase of infection.
CDC notes that some NAATs may remain positive for up to approximately 90 days.
What Is a Rapid Antigen Test?
Antigen tests detect specific viral proteins.
Many home COVID-19 tests are antigen tests.
Advantages include:
- Fast results
- Convenience
- No laboratory required
- Relatively low cost
However, they are less sensitive than PCR, especially early in infection or in people without symptoms.
Does a Negative Home Test Rule Out COVID-19?
No.
A single negative antigen test cannot reliably rule out infection.
FDA recommends repeat testing.
For someone with symptoms:
- Test again approximately 48 hours after the first negative antigen test.
For someone without symptoms:
- Repeat after 48 hours.
- If still negative, repeat again 48 hours later.
This means an asymptomatic person may need three antigen tests over approximately five days to reduce the risk of missing an infection.
Are Antibody Tests Used to Diagnose Current COVID-19?
No.
Antibody tests show immune responses to previous infection or vaccination.
They are not recommended for diagnosing a current SARS-CoV-2 infection.
How Is Mild COVID-19 Treated?
Many healthy people with mild disease recover at home.
Supportive care may include:
- Rest
- Fluids
- Appropriate fever treatment
- Appropriate pain relief
- Monitoring symptoms
- Avoiding transmission to others
However, people at higher risk of severe disease may benefit from antiviral medication even if their initial symptoms appear mild.
The treatment window is short.
Why Is Early Treatment Important?
Antiviral treatment works best when started early, while SARS-CoV-2 is actively replicating.
CDC recommends considering treatment for patients with mild or moderate COVID-19 who have risk factors for progression to severe illness.
Treatment generally needs to start within 5 to 7 days of symptom onset, depending on the medication.
Waiting until someone becomes severely ill may eliminate the opportunity to use certain outpatient antivirals.
What Is Paxlovid?
Paxlovid contains two antiviral medicines:
- Nirmatrelvir
- Ritonavir
Nirmatrelvir inhibits a SARS-CoV-2 protease needed for viral replication.
Ritonavir slows metabolism of nirmatrelvir, allowing effective concentrations to remain in the body.
Paxlovid is taken orally for 5 days.
Treatment should begin within 5 days of symptom onset.
Who Can Receive Paxlovid?
CDC lists Paxlovid for:
- Adults
- Eligible children aged 12 years and older who weigh at least 40 kilograms
when they have mild or moderate COVID-19 and are at increased risk for progression to severe disease.
The FDA fully approved Paxlovid for eligible high-risk adults in May 2023.
Certain pediatric use has continued under applicable regulatory mechanisms.
Does Paxlovid Interact With Other Medications?
Yes.
Ritonavir strongly affects enzymes that metabolize many medicines.
Important interactions can occur with medications used for:
- Heart disease
- Abnormal heart rhythms
- Cholesterol
- Seizures
- Transplantation
- Other medical conditions
A healthcare professional should review the patient’s medications before treatment.
Kidney and liver function can also influence eligibility or dosage.
What Is Paxlovid Rebound?
Some people experience improvement followed by:
- Return of symptoms
- A new positive test
- Both
after completing treatment.
Similar rebound can also occur after untreated COVID-19.
A rebound episode does not automatically mean antiviral treatment failed.
People experiencing recurrent symptoms should follow current public-health precautions and contact a healthcare professional if symptoms become severe or they are at high risk.
What Is Remdesivir?
Remdesivir, marketed as Veklury, is an antiviral medication administered intravenously.
For eligible outpatients at increased risk of severe disease, CDC describes a 3-day intravenous course started within 7 days of symptom onset.
It can also be used in hospitalized patients in appropriate circumstances.
Remdesivir became the first drug to receive full FDA approval specifically for COVID-19 in October 2020.
What Is Molnupiravir?
Molnupiravir, marketed as Lagevrio, is another oral antiviral option.
CDC generally describes it as an alternative when preferred options cannot be used or are unavailable.
It is taken for five days and should begin within five days of symptom onset.
It is not recommended during pregnancy because of concerns about effects on a developing fetus.
Are Antibiotics Used for COVID-19?
Antibiotics do not kill SARS-CoV-2.
COVID-19 is viral.
Antibiotics are appropriate only when a healthcare professional suspects or confirms a bacterial infection occurring separately or as a complication.
Using antibiotics unnecessarily can contribute to antibiotic resistance.
How Is Severe COVID-19 Treated?
Hospital treatment depends on disease severity.
Patients may require:
- Oxygen
- Antiviral treatment
- Corticosteroids in appropriate patients
- Other immune-modifying medications
- Blood-clot prevention
- Intravenous fluids
- Respiratory support
- Mechanical ventilation
- Intensive-care treatment
- Kidney support
Treatment recommendations have changed considerably since 2020 as clinical trials identified therapies that improve outcomes.
Is There a COVID-19 Vaccine?
Yes.
COVID-19 vaccines are available and continue to be updated as SARS-CoV-2 evolves.
In the United States, currently available vaccine technology includes:
- mRNA vaccines
- Protein-subunit vaccines
Current FDA-approved brands include:
- Comirnaty
- Spikevax
- mNexspike
- Nuvaxovid
How Do mRNA COVID-19 Vaccines Work?
mRNA vaccines contain genetic instructions that allow cells to temporarily produce a selected piece of SARS-CoV-2 spike protein.
The immune system recognizes this protein as foreign.
It develops:
- Antibodies
- B-cell memory
- T-cell responses
The vaccine mRNA does not need to enter the cell nucleus.
It is eventually broken down by normal cellular processes.
How Does the Novavax Vaccine Work?
Nuvaxovid uses a protein-subunit approach.
Instead of providing mRNA instructions, the vaccine contains recombinant SARS-CoV-2 spike protein together with an immune-stimulating adjuvant.
The immune system responds to the protein and develops immune memory.
Why Do COVID-19 Vaccines Need Updating?
SARS-CoV-2 continually evolves.
Mutations in spike protein can change how well existing antibodies recognize the virus.
Updating vaccine antigens can improve the immune response against more recently circulating lineages.
The concept is somewhat similar to periodically updating influenza vaccines, although the biology and regulatory process are not identical.
What Is the 2026-2027 COVID-19 Vaccine Formula?
For the U.S. 2026-2027 season, FDA advised manufacturers that updated vaccines should be monovalent vaccines targeting the JN.1-lineage XFG variant.
The recommendation followed an FDA advisory committee review on May 28, 2026 of:
- Circulating variants
- Antigenic differences
- Vaccine effectiveness
- Human immune-response data
- Laboratory data
- Manufacturing considerations
The updated products began receiving approvals in August 2026.
Which COVID-19 Vaccines Are Available in the United States in 2026?
FDA lists four approved COVID-19 vaccine brands:
| Vaccine | Type |
|---|---|
| Comirnaty | mRNA |
| Spikevax | mRNA |
| mNexspike | mRNA |
| Nuvaxovid | Protein subunit |
FDA labeling for the 2026-2027 products is based on age and risk.
For example:
- Spikevax is FDA approved for adults 65 years and older and for people aged 6 months through 64 years who have at least one underlying condition associated with increased risk of severe COVID-19.
- mNexspike is approved for adults 65 years and older and people aged 12 through 64 with at least one high-risk underlying condition.
- Nuvaxovid is approved for adults 65 years and older and people aged 12 through 64 with at least one high-risk underlying condition.
What Does CDC Recommend for the 2026-2027 Season?
U.S. recommendations changed substantially during 2025 and 2026.
CDC’s clinical considerations updated September 23, 2026 state that the July 2025 immunization schedule recommendations remain in effect for the 2026-2027 respiratory illness season while reflecting current FDA regulatory information.
CDC currently states:
- A 2026-2027 COVID-19 vaccine is recommended for adults aged 18 years and older.
- Vaccination is recommended for children aged 6 months through 17 years with moderate or severe immunocompromise.
- For other children, vaccination is based on shared clinical decision-making.
CDC also notes that some recommended uses may be outside the specific FDA-approved indication and identifies these situations as off-label in its clinical guidance.
Because recommendations and regulatory indications can change, patients should use the current CDC schedule and FDA product labeling when deciding which product and dose are appropriate.
Does Previous COVID-19 Infection Mean Vaccination Is Unnecessary?
Not necessarily.
Previous infection produces immune protection, but that protection changes over time and can be partially bypassed by new variants.
CDC vaccination guidance therefore considers both previous vaccination and current risk rather than treating previous infection as permanent protection.
Can COVID-19 Vaccines Cause Side Effects?
Yes.
Most vaccine reactions are mild to moderate and resolve within approximately 1 to 3 days.
Common reactions include:
- Injection-site pain
- Swelling
- Redness
- Fatigue
- Headache
- Muscle aches
- Chills
- Fever
- Joint pain
- Swollen lymph nodes
Can COVID-19 Vaccines Cause Myocarditis?
Myocarditis and pericarditis have rarely occurred following COVID-19 vaccination.
Cases have historically been observed most frequently among adolescent and young adult males, particularly within approximately one week after an mRNA vaccine dose.
CDC also notes evidence of increased myocarditis and pericarditis risk following Novavax vaccination.
The complication remains uncommon.
Someone developing:
- Chest pain
- Shortness of breath
- Palpitations
after vaccination should seek medical evaluation.
Can a COVID-19 Vaccine Cause a Severe Allergic Reaction?
Rarely.
Anaphylaxis can occur after vaccination, as it can with other vaccines and medications.
CDC has historically estimated anaphylaxis at approximately 5 cases per million COVID-19 vaccine doses.
People with a previous severe allergic reaction to a specific vaccine or vaccine component should discuss alternative products and precautions with a healthcare professional.
How Can COVID-19 Be Prevented?
No single prevention measure eliminates all risk.
Protection works best by combining measures according to personal risk and the amount of virus circulating in the community.
Important strategies include:
- Appropriate vaccination
- Staying home when sick
- Improving indoor air quality
- Using well-fitting masks in higher-risk situations
- Testing when appropriate
- Avoiding close exposure to vulnerable people while infectious
- Hand hygiene
- Seeking early treatment if high-risk
Why Does Ventilation Matter?
SARS-CoV-2 spreads through respiratory particles.
Indoor environments allow those particles to accumulate, particularly when ventilation is poor.
Strategies that can reduce airborne exposure include:
- Opening windows when practical
- Improving mechanical ventilation
- Using effective HVAC filtration
- Portable HEPA filtration
- Increasing outdoor-air exchange
CDC continues to emphasize ventilation and cleaner indoor air as components of respiratory-virus prevention.
Do Masks Still Help?
Yes.
CDC describes masking as an additional layer of protection against respiratory-virus transmission.
A well-fitting mask can:
- Reduce infectious particles emitted by a sick person
- Reduce the amount of infectious material inhaled by the wearer
Masks can be particularly useful:
- When respiratory illness is increasing
- In crowded indoor settings
- After recent exposure
- During recovery from illness
- Around people at high risk of severe disease
What Should Someone Do When They Have COVID-19 Symptoms?
Current CDC respiratory-virus guidance advises staying home and away from others when experiencing respiratory symptoms that are not better explained by another cause.
A person can generally return toward normal activities when, for at least 24 hours:
- Symptoms are improving overall
- Any fever has resolved without fever-reducing medication
Additional precautions can then be useful for the following days, particularly around vulnerable people.
These can include:
- Masking
- Cleaner air
- Testing
- Physical distancing
- Good hygiene
What If Someone Tests Positive but Has No Symptoms?
An asymptomatic person can still potentially transmit SARS-CoV-2.
CDC recommends using added precautions for approximately five days after a positive result, including measures such as:
- Cleaner air
- Masking
- Distancing
- Testing
- Avoiding vulnerable people
When Should Someone Seek Emergency Care?
COVID-19 can occasionally deteriorate rapidly.
CDC lists emergency warning signs including:
- Trouble breathing
- Persistent pain or pressure in the chest
- New confusion
- Inability to wake or remain awake
- Pale, gray, or blue-colored lips, skin, or nail beds depending on skin tone
Any symptom that appears severe or life-threatening requires urgent medical assessment.
When Should a High-Risk Person Contact a Doctor?
People at increased risk should seek medical advice early, ideally as soon as they develop symptoms or test positive.
This is important because antiviral treatment must begin quickly.
Paxlovid must generally start within 5 days of symptoms.
Outpatient remdesivir should generally begin within 7 days.
Waiting to see whether symptoms become severe can result in missing the treatment window.
Frequently Asked Questions About COVID-19
What does COVID-19 stand for?
COVID-19 means Coronavirus Disease 2019.
The number 19 refers to the year the disease first emerged.
What virus causes COVID-19?
COVID-19 is caused by SARS-CoV-2.
Is SARS-CoV-2 the same thing as COVID-19?
No.
SARS-CoV-2 is the virus.
COVID-19 is the disease caused by the virus.
When was COVID-19 first discovered?
The first recognized cluster of unexplained pneumonia associated with the outbreak was reported in Wuhan, China, in December 2019.
When was the disease named COVID-19?
WHO announced the name COVID-19 in February 2020.
When was COVID-19 declared a pandemic?
WHO characterized COVID-19 as a pandemic on March 11, 2020.
Is COVID-19 still a pandemic?
The extraordinary emergency phase has ended.
WHO ended the COVID-19 Public Health Emergency of International Concern on May 5, 2023.
However, SARS-CoV-2 continues circulating worldwide and still causes severe illness and death. WHO assessed the global public-health risk as moderate in July 2026.
Did COVID-19 disappear after the emergency ended?
No.
Ending the emergency declaration did not mean the virus disappeared.
COVID-19 continues circulating globally.
How does COVID-19 spread?
It spreads primarily through infectious respiratory particles released by infected people.
Can someone spread COVID-19 without symptoms?
Yes.
Transmission can occur before symptoms develop and from people who remain asymptomatic.
How long after exposure do symptoms begin?
It varies.
During Omicron-dominant periods, studies found a median incubation period of approximately 3 to 4 days.
Is COVID-19 just a cold?
No.
Some infections resemble a common cold, but COVID-19 can also cause pneumonia, hospitalization, organ complications, Long COVID, and death.
Is COVID-19 the same as influenza?
No.
Influenza and COVID-19 are different diseases caused by different viruses.
Their symptoms can overlap so much that laboratory testing may be necessary to distinguish them.
Can COVID-19 cause diarrhea?
Yes.
Gastrointestinal symptoms including nausea, vomiting, and diarrhea can occur.
Is loss of smell still associated with COVID-19?
Yes, but it is less common than it was before Omicron became dominant.
Can you have COVID-19 more than once?
Yes.
Reinfection can occur repeatedly.
Can you get COVID-19 after vaccination?
Yes.
Vaccination does not prevent every infection, but it can reduce the risk of severe outcomes.
Can COVID-19 cause long-term symptoms?
Yes.
Long COVID can persist for months or years and can affect multiple organ systems.
How long does Long COVID last?
There is no single duration.
Some people improve within months.
Others experience symptoms for years.
Can children develop Long COVID?
Yes.
Anyone infected with SARS-CoV-2 can potentially develop Long COVID, including children.
What is MIS-C?
MIS-C is a rare inflammatory condition that can develop several weeks after SARS-CoV-2 infection in children.
It may affect the heart, gastrointestinal system, skin, eyes, lungs, brain, and other organs.
Does a negative rapid test mean I definitely do not have COVID-19?
No.
Antigen tests can miss infection, particularly early.
FDA recommends repeat testing approximately 48 hours later after a negative antigen test.
Is PCR more sensitive than a home antigen test?
Generally, yes.
NAATs such as PCR can detect lower amounts of viral genetic material.
Can PCR stay positive after someone recovers?
Yes.
Some NAATs may remain positive for up to approximately 90 days after infection.
Do antibiotics cure COVID-19?
No.
COVID-19 is viral.
Antibiotics should be used only when a bacterial infection is present or suspected.
Is there antiviral treatment for COVID-19?
Yes.
Major outpatient antiviral options for eligible high-risk patients include:
- Paxlovid
- Remdesivir
- Molnupiravir in selected circumstances
How soon must Paxlovid be started?
Generally within 5 days of symptom onset.
Is remdesivir still used?
Yes.
For eligible outpatients it may be administered intravenously for 3 consecutive days, beginning within 7 days of symptom onset.
Is there a COVID-19 vaccine?
Yes.
Multiple COVID-19 vaccines are FDA approved in the United States.
Which COVID-19 vaccines are currently available in the U.S.?
FDA currently lists:
- Comirnaty
- Spikevax
- mNexspike
- Nuvaxovid
What variant does the 2026-2027 vaccine target?
FDA recommended a monovalent vaccine targeting the JN.1-lineage XFG variant for the U.S. 2026-2027 season.
Why are COVID vaccines updated?
SARS-CoV-2 continually evolves.
Updating the vaccine allows the immune response to more closely match currently circulating viruses.
Are COVID-19 vaccines safe?
The vaccines have undergone extensive clinical testing and safety monitoring.
Most reactions are mild and temporary.
Rare serious reactions include anaphylaxis and myocarditis or pericarditis.
Can a COVID vaccine cause myocarditis?
Rarely.
The association has been seen most often in adolescent and young adult males after mRNA vaccination, although cases have occurred in other groups and myocarditis risk has also been observed after Novavax vaccination.
Can pregnant people receive COVID-19 vaccination?
Current U.S. recommendations involve individualized decision-making depending on age, health status, and current guidance.
Pregnancy itself increases the risk of severe COVID-19, and CDC reports that vaccination during pregnancy has not been associated with increased health risks for pregnant people or babies in available monitoring.
Can COVID-19 cause death?
Yes.
Although population immunity, vaccines, treatments, and improved clinical care have substantially reduced risk compared with the earliest pandemic period, COVID-19 continues to cause deaths worldwide.
How many people have died from COVID-19 worldwide?
WHO reported more than 7 million confirmed COVID-19 deaths worldwide by June 28, 2026.
The true pandemic mortality burden is larger than confirmed death counts alone because surveillance was incomplete in many countries.
How many confirmed COVID-19 cases have occurred?
WHO reported more than 779 million confirmed cases by June 28, 2026.
Actual infections are far higher because many infections were never tested, reported, or recorded, and many people have been infected multiple times.
Are new COVID variants still appearing?
Yes.
SARS-CoV-2 continues evolving and producing new lineages.
WHO continues international variant monitoring.
Is Omicron still relevant?
Yes.
Most recent major lineages descend from the broader Omicron evolutionary family.
Later descendants have accumulated numerous additional genetic changes.
Can another major COVID wave happen?
Future transmission surges remain possible because SARS-CoV-2 continues circulating, immunity changes with time, and new variants continue emerging.
The severity of any future wave depends on factors including:
- Variant properties
- Population immunity
- Vaccination
- Age distribution
- Treatment availability
- Healthcare capacity
Can COVID-19 eventually be eradicated?
Complete global eradication is considered extremely difficult.
SARS-CoV-2:
- Spreads efficiently
- Can cause asymptomatic infection
- Evolves rapidly
- Produces reinfections
- Has infected animal species
- Circulates internationally
Current public-health efforts therefore focus largely on reducing severe disease, deaths, long-term consequences, and transmission to vulnerable people rather than expecting complete global elimination.
Why COVID-19 Changed Modern Medicine
COVID-19 transformed infectious-disease medicine in a remarkably short period.
At the end of 2019, the disease had no name.
The virus had not been identified.
There was no diagnostic test.
There was no vaccine.
There was no proven antiviral treatment.
Within weeks, scientists had sequenced SARS-CoV-2 and developed PCR testing.
Within months, large international clinical trials were evaluating treatments.
By October 2020, remdesivir had become the first FDA-approved COVID-19 treatment.
By December 2020, the first COVID-19 vaccines were being administered under emergency authorization in the United States.
In August 2021, Comirnaty became the first fully FDA-approved COVID-19 vaccine.
The virus continued changing.
Alpha emerged.
Delta produced devastating outbreaks.
Omicron appeared in late 2021 and rapidly reshaped the pandemic.
Successive Omicron descendants increasingly encountered populations with complex combinations of immunity from vaccination, previous infection, or both.
Medicine adapted as well.
Testing moved from specialized laboratories into people’s homes.
Oral antiviral medication became available.
Vaccines were reformulated to better match circulating variants.
Scientists identified Long COVID as an important chronic consequence of SARS-CoV-2 infection.
COVID-19 also accelerated research into:
- mRNA vaccines
- Genomic surveillance
- Rapid diagnostic testing
- Antiviral development
- Indoor-air quality
- Pandemic preparedness
- Infection-associated chronic illness
- Global pathogen surveillance
The emergency stage eventually ended, but the disease did not.
WHO ended the COVID-19 Public Health Emergency of International Concern on May 5, 2023.
More than three years later, SARS-CoV-2 was still circulating worldwide.
WHO’s August 2026 assessment continued to classify the global public-health risk as moderate and emphasized that older adults, immunocompromised people, and individuals with certain underlying conditions remain particularly vulnerable.
COVID-19 therefore occupies a different place in medicine today than it did in 2020.
For many people, infection now produces a short respiratory illness.
For others, particularly those at higher risk, it can still lead to hospitalization, organ complications, or death.
For another group, even an initially mild infection can be followed by months or years of Long COVID symptoms.
The continuing challenge is therefore not simply preventing every infection.
Modern COVID-19 control involves several goals at the same time:
- Preventing severe disease
- Protecting vulnerable people
- Providing early antiviral treatment
- Updating vaccines as the virus evolves
- Improving indoor-air quality
- Reducing transmission during illness
- Identifying and treating complications
- Understanding and managing Long COVID
- Monitoring new variants
- Maintaining preparedness for future changes in the virus
More than six years after the first recognized cases, COVID-19 has moved from a completely unknown disease to one of the most intensively studied infections in medical history.
Yet important questions remain, particularly about viral evolution, repeated reinfection, long-term health consequences, optimal vaccination strategies, and Long COVID.
SARS-CoV-2 continues to evolve, and medical recommendations will continue evolving with it.
Medical, vaccine, treatment, and epidemiological information reviewed against CDC, FDA, WHO, and current public-health guidance available through September 2026.