Introduction
The COVID-19 vaccine remains an important tool for reducing the risk of severe illness, hospitalization, and death caused by COVID-19. COVID-19 is caused by the SARS-CoV-2 virus, which continues to circulate even though its overall impact on health systems has declined substantially compared with the early years of the pandemic. Older adults, people with certain medical conditions, and people with weakened immune systems remain at greater risk of severe disease.
COVID-19 vaccines work by preparing the immune system to recognize SARS-CoV-2. Although vaccination cannot guarantee that someone will never become infected, current evidence shows that vaccines continue to provide meaningful protection against severe disease and death. Protection against severe outcomes can decline over time, which is why health authorities may recommend periodic vaccination for people at higher risk.
Vaccine recommendations have changed as the virus, available vaccines, and population immunity have changed. In 2026, WHO uses a risk-based approach, with particular emphasis on people who are most likely to develop severe COVID-19.
This guide explains what the COVID-19 vaccine is, how it works, its benefits, types, effectiveness, side effects, vaccination schedules, and who may benefit most from staying up to date.
What Is the COVID-19 Vaccine?
A COVID-19 vaccine is a medical product designed to stimulate an immune response against SARS-CoV-2.
Different COVID-19 vaccines use different technologies. WHO currently describes two major vaccine technology categories: mRNA vaccines and protein-based vaccines.
Rather than causing COVID-19, vaccines train the immune system to recognize important features of the virus. If a vaccinated person later encounters SARS-CoV-2, the immune system may respond more rapidly and effectively.
The goal of vaccination is particularly important for preventing severe outcomes rather than guaranteeing complete prevention of infection.
How Does the COVID-19 Vaccine Work?
Vaccines introduce the immune system to an antigen or information that allows the body to recognize the virus.
After vaccination, the immune system develops protective responses, including antibodies and immune memory. If the person later encounters SARS-CoV-2, these defenses can help control the infection.
Protection is not permanent at the same level. WHO reports that protection against severe disease and death is highest during the first few months after vaccination and gradually decreases over time. Immunity can also decline following infection.
This is one reason updated or periodic vaccination may be recommended for people at higher risk.
Main Types of COVID-19 Vaccines
mRNA Vaccines
mRNA vaccines use messenger RNA to provide temporary instructions that help cells produce a harmless piece of the virus. The immune system recognizes this protein and develops an immune response.
The mRNA does not permanently change a person’s DNA.
Protein-Based Vaccines
Protein-based vaccines use harmless viral proteins or protein components to stimulate immunity. They do not contain a complete live SARS-CoV-2 virus capable of causing COVID-19.
Updated Variant-Adapted Vaccines
SARS-CoV-2 continues to evolve. Vaccine compositions can therefore be updated to improve the immune response against currently circulating or recently circulating variants.
In May 2026, WHO’s Technical Advisory Group recommended monovalent LP.8.1 as the preferred antigen composition while also noting that other formulations capable of producing broad protection may be used. WHO also stated that vaccination should not be delayed simply while waiting for a newer formulation to become available.
Benefits of the COVID-19 Vaccine
Reduces the Risk of Severe COVID-19
The most important benefit of vaccination is protection against serious disease.
WHO states that currently available COVID-19 vaccines provide protection against severe disease and death.
Helps Reduce Hospitalization
Vaccination can lower the likelihood that an infected person will become seriously ill enough to require hospital care.
Helps Reduce the Risk of Death
Vaccines have saved millions of lives globally by reducing severe COVID-19, hospitalization, and death.
Provides Additional Protection for High-Risk People
Older adults and people with certain chronic health conditions or weakened immune systems may receive particular benefit because their risk of severe COVID-19 is higher.
Supports Community Protection
Vaccination contributes to population immunity and can help reduce the overall health burden caused by COVID-19, although vaccines do not completely prevent transmission.
Can You Still Get COVID-19 After Vaccination?
Yes.
COVID-19 vaccines are not 100% effective at preventing infection. A vaccinated person can still become infected and develop what is sometimes called a breakthrough infection.
However, the main benefit of vaccination is protection against severe outcomes. WHO notes that vaccinated people who become infected are more likely to experience milder illness because protection against severe disease and death remains substantial.
Therefore, getting COVID-19 after vaccination does not necessarily mean that the vaccine has failed.
Who Should Get a COVID-19 Vaccine?
Recommendations depend on national policy, age, health status, previous vaccination, previous infection, and the risk of severe disease.
WHO’s 2026 recommendations place particular emphasis on people at the highest risk of severe COVID-19, including:
- Older adults
- People with significant underlying health conditions
- People with weakened immune systems
- Certain other high-risk groups identified by national health authorities
WHO suggests that countries consider routine vaccination for their highest-risk populations and determine age thresholds according to local circumstances.
Because recommendations differ between countries, people should follow the current guidance of their national health authority or healthcare professional.
COVID-19 Vaccine Schedule
There is no single schedule that applies to everyone worldwide.
Current vaccination recommendations are increasingly risk-based rather than relying on the same schedule for every person.
WHO’s 2026 guidance recommends
that countries consider at least annual vaccination for certain highest-risk groups, including the oldest adults, with the exact age threshold determined nationally.
People who are immunocompromised or have other significant risk factors may have different vaccination needs.
For this reason, the correct number and timing of doses should be determined according to the vaccine available in your country and your individual circumstances.
Do Healthy Young People Need COVID-19 Vaccination?
The answer depends on national recommendations and individual circumstances.
WHO’s current guidance places the strongest emphasis on people at higher risk of severe disease. Healthy children and adolescents generally have a lower risk of severe COVID-19, and WHO does not routinely recommend revaccination for healthy children and adolescents in the post-pandemic setting.
National recommendations may differ based on local disease patterns, vaccine availability, and public-health policy.
COVID-19 Vaccine for Older Adults
Older adults are among the groups most likely to develop severe COVID-19.
WHO’s 2026 recommendations suggest that countries consider routine vaccination for their oldest adults, with a suggested threshold of approximately 75 or 80 years depending on national policy. For these highest-risk groups, WHO recommends at least one dose per year when the previous dose was more than six months earlier.
People with additional risk factors may require individualized advice.
COVID-19 Vaccine During Pregnancy
Pregnant people can be at increased risk of complications from respiratory infections, including COVID-19.
Vaccination recommendations during pregnancy depend on current national guidance, individual risk, and vaccine availability. Anyone who is pregnant and considering vaccination should discuss the appropriate timing and product with a healthcare professional.
WHO continues to include pregnancy among groups for whom COVID-19 vaccination may be important based on risk.
COVID-19 Vaccine Side Effects
Most COVID-19 vaccine reactions are mild or moderate and temporary.
Common side effects may include:
- Pain at the injection site
- Redness or swelling
- Fatigue
- Headache
- Muscle aches
- Chills
- Mild fever
- Joint discomfort
These reactions usually improve within a few days. WHO reports that most COVID-19 vaccine reactions are mild or moderate and short-lived.
Experiencing no side effects does not mean that a vaccine has failed. People respond differently to vaccination.
Serious Side Effects and Allergic Reactions
Serious adverse events following COVID-19 vaccination are uncommon.
Vaccines are monitored continuously after introduction into vaccination programs. National health authorities and international organizations look for unusual patterns that could indicate a safety concern.
A severe allergic reaction, known as anaphylaxis, is extremely rare but requires immediate medical treatment.
Anyone who develops difficulty breathing, swelling of the face or throat, severe dizziness, or other signs of a severe allergic reaction after vaccination should seek emergency medical care.
Are COVID-19 Vaccines Safe?
COVID-19 vaccines have undergone clinical testing and extensive safety monitoring.
WHO reports that more than 13 billion COVID-19 vaccine doses had been administered globally and that accumulated safety data show a favorable overall safety profile. Serious adverse events remain extremely rare compared with the number of doses administered.
Like all medical products, vaccines can have side effects. The decision to vaccinate should take into account both benefits and potential risks, particularly for people with specific medical conditions or previous serious vaccine reactions.
How Effective Is the COVID-19 Vaccine?
Effectiveness depends on several factors, including:
- The vaccine formulation
- The circulating variant
- Time since vaccination
- Previous infection
- Age
- Immune-system function
- The outcome being measured
Current vaccines are particularly valuable for reducing severe disease and death. WHO reports that real-world evidence continues to demonstrate protection against severe COVID-19.
Protection against infection and symptomatic disease can be less consistent and can decrease as immunity wanes.
This is why vaccine effectiveness should not be judged solely by whether vaccinated people ever become infected.
Why Are COVID-19 Vaccines Updated?
SARS-CoV-2 changes over time through genetic evolution. Some variants can differ enough from earlier versions of the virus that updating the vaccine antigen can improve the match between vaccination and circulating viruses.
WHO’s vaccine composition group regularly evaluates:
- New SARS-CoV-2 variants
- Genetic changes
- Antibody responses
- Vaccine effectiveness
- Evidence from clinical and real-world studies
In May 2026, WHO recommended LP.8.1 as the preferred vaccine antigen while continuing to monitor emerging variants.
Can COVID-19 Vaccination Prevent Long COVID?
COVID-19 vaccination is primarily intended to reduce the risk of severe acute disease.
Research has also examined whether vaccination influences the risk of post-COVID condition, commonly called Long COVID. Evidence suggests vaccination may reduce the risk of developing Long COVID in some circumstances, but vaccination does not guarantee that the condition will be prevented.
People should continue to follow medical guidance for persistent symptoms after COVID-19 infection.
Can You Get Other Vaccines at the Same Time?
COVID-19 vaccination can sometimes be administered during the same visit as other vaccines.
WHO states that receiving multiple vaccines during one visit can be safe and that combination vaccination does not overwhelm the immune system.
However, the exact vaccines and timing should follow current national recommendations and the advice of a healthcare professional.
What If You Previously Had COVID-19?
Previous infection can provide some immunity, but the level and duration of protection vary.
Vaccination can provide additional protection, especially against severe disease. WHO notes that both infection- and vaccine-derived immunity can decline over time.
The recommended timing of vaccination after infection can vary according to national guidelines, age, risk level, and previous vaccination history.
COVID-19 Vaccine and Immune System
Vaccines work by training the immune system rather than weakening it.
After vaccination, the immune system develops targeted defenses against SARS-CoV-2. When the body later encounters the virus, immune memory can help it respond more quickly.
The immune response varies between individuals, which is one reason protection is not identical for everyone.
Who Should Talk to a Doctor Before Vaccination?
Most people can receive recommended COVID-19 vaccines safely, but medical advice may be especially useful if you:
- Previously experienced a severe allergic reaction to a vaccine
- Have a history of a serious reaction after a COVID-19 vaccine
- Are pregnant
- Are significantly immunocompromised
- Have a serious current illness
- Take medications that affect the immune system
- Have questions about the appropriate vaccine or schedule
A healthcare professional can review your medical history and determine the most suitable vaccination plan.
COVID-19 Vaccine and Children
Children can become infected with SARS-CoV-2, but healthy children and adolescents generally have a lower risk of severe disease than older adults.
WHO’s current recommendations do not routinely recommend revaccination for healthy children and adolescents in the post-pandemic setting. However, countries may consider vaccination for previously unvaccinated children aged 6–23 months when there is a documented significant disease burden in that age group.
Parents should follow the vaccination recommendations issued by their country’s health authorities.
How to Stay Protected From COVID-19
Vaccination is only one part of reducing the risk of serious respiratory illness.
Other practical measures include:
- Staying home when you are sick
- Improving indoor ventilation
- Avoiding close contact with people who are acutely ill
- Washing hands regularly
- Following local public-health recommendations during outbreaks
- Seeking medical advice promptly if you are at high risk and develop COVID-19 symptoms
People at increased risk of severe disease should have a plan for accessing medical care if they become infected.
Conclusion
The COVID-19 vaccine continues to play an important role in protecting people from severe COVID-19, hospitalization, and death. Although vaccination cannot guarantee complete protection from infection, current evidence shows that vaccines provide meaningful protection against serious outcomes, particularly among people at higher risk.
COVID-19 vaccination recommendations have evolved as SARS-CoV-2 has changed and population immunity has increased. In 2026, WHO emphasizes a risk-based approach that prioritizes older adults and other people who are most vulnerable to severe disease. Vaccine formulations are also periodically updated to better match circulating variants.
Most vaccine reactions are mild and temporary, while serious adverse events are rare. The best vaccination schedule depends on age, health status, previous vaccination, previous infection, vaccine product, and national guidance.
If you are unsure whether you need a COVID-19 vaccine, booster, or updated dose, speak with a healthcare professional or check the latest recommendations from your national health authority.
FAQs About COVID-19 Vaccine
1. What is the COVID-19 vaccine?
The COVID-19 vaccine is designed to train the immune system to recognize SARS-CoV-2 and reduce the risk of serious COVID-19. Different vaccines use technologies such as mRNA or protein-based platforms.
2. Can you still get COVID-19 after vaccination?
Yes. Vaccination does not provide 100% protection against infection. However, it continues to provide important protection against severe disease and death.
3. What are the common COVID-19 vaccine side effects?
Common reactions include injection-site pain, fatigue, headache, muscle aches, chills, and mild fever. Most are temporary and resolve within a few days.
4. Is the COVID-19 vaccine safe?
WHO reports that extensive safety data show a favorable safety profile for COVID-19 vaccines, with serious adverse events being extremely rare compared with the number of doses administered.
5. How often should I get a COVID-19 vaccine?
There is no single schedule for everyone. Current WHO recommendations emphasize periodic vaccination for people at highest risk, with at least annual vaccination suggested for certain highest-risk groups when the previous dose was more than six months earlier. National recommendations may differ.
6. Can COVID-19 vaccines prevent severe illness?
Yes. Preventing severe disease, hospitalization, and death is one of the most important benefits of COVID-19 vaccination.
7. Why are COVID-19 vaccines updated?
SARS-CoV-2 continues to evolve. Vaccine formulations can be updated to improve immune responses against currently circulating variants. WHO recommended LP.8.1 as the preferred antigen composition in May 2026.
8. Should older adults get COVID-19 vaccination?
Older adults have a higher risk of severe COVID-19. WHO recommends that countries consider routine vaccination for their oldest adults, with the exact age threshold determined by national policy.
9. Can I get another vaccine during the same visit as a COVID-19 vaccine?
Multiple vaccines can be administered during the same visit when recommended. WHO states that receiving multiple vaccines during one visit can be safe.
10. What should I do if I am unsure whether I need a COVID-19 vaccine?
Discuss your vaccination history, age, medical conditions, previous COVID-19 infection, and current vaccine availability with a healthcare professional. They can help determine whether you are due for an updated dose according to current local recommendations.
