All of these answers are provisional. The content is updated as more information is made available.
Last update: 9/26/2022
As of September 2022, the World Health Organization (WHO) has issued recommendations for the use of the COVID-19 vaccines produced by the following manufacturers: Pfizer/BioNTech, AstraZeneca/Oxford, Janssen, Moderna, Sinopharm, Sinovac, Bharat, Novavax, Casino, and Valneva. WHO continues to evaluate other vaccines in both clinical and pre-clinical trial. Additionally, the national regulatory authority (NRA) of some countries authorized the use of additional COVID-19 vaccines in their territory.
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Messenger RNA (mRNA) vaccines teach our cells how to make a protein that will trigger an immune response inside our bodies. Like all vaccines, mRNA vaccines benefit people by giving them protection against diseases like COVID-19 without risking the potentially serious consequences of getting sick. mRNA vaccine technology is new but not unknown. Researchers have been studying and working with them for decades for other diseases like influenza and Zika.
WHO-recommended COVID-19 vaccines are highly effective in preventing severe illness, hospitalization and death against all strains of the SARS-CoV-2 virus (i.e., the virus that causes COVID-19), including the Delta and Omicron variants. Also, vaccines are highly effective in reducing transmission of the virus, although they may not prevent infection completely.
Data on new variants of SARS-CoV-2 continue to be collected and analyzed through global laboratory networks. WHO is in close communication with researchers, health officials and scientists to learn how these variants may affect the properties of the vaccines.
COVID-19 vaccines are highly effective and are a critical tool to bring the pandemic under control. However, no vaccines are 100% effective at preventing illness in vaccinated people. There will be a small percentage of fully vaccinated people who still get sick. This is known as a ‘breakthrough infection’. With highly transmissible variants like Omicron, we are seeing more breakthrough infections and cases. Symptoms will likely be mild or absent in vaccinated persons who become infected.
Also, full protection of the vaccine starts 14 days after the administration of the second dose of vaccine. A person may contract the SARS-COV-2 virus immediately before or soon after receiving the COVID-19 vaccine, and therefore not be fully protected despite vaccination.
Since vaccines against COVID-19 are available in all countries of the Americas, you will be able to access them through your National Immunization Program. Contact your closest health care center or pharmacy to obtain more information.
PAHO encourages people to get vaccinated against COVID-19 with whatever vaccine is offered to them. All authorized vaccines have proven to be safe and effective at preventing COVID-19 by the national regulatory authority of each country.
For more information on the different vaccines please visit:
As of September 2022, we are still learning how long the protection of COVID-19 vaccines lasts, since the first person ever to receive the vaccine has been protected for fewer than two years. Available data suggest that most people who recover from COVID-19 develop an immune response that provides at least 6 months of protection against reinfection. To avoid declining protection over time, WHO recommends that all eligible persons should receive one booster dose of any WHO-approved COVID-19 vaccine 4-6 months after the administration of the second dose of vaccine or as soon as possible after the 6 months.
At this time, only persons aged 18 years or older are eligible to receive booster doses of the COVID-19 vaccine.
WHO does not keep a record of the persons who have been vaccinated in each country. Therefore, WHO does not issue an International Certificate of Vaccination or Prophylaxis Card for vaccines against COVID-19. The government-issued vaccination document is the only proof of vaccination against COVID-19 that is currently available.
An international traveller should follow the health requirements issued by the countries where they travel.
To protect yourself and others from COVID-19, get up to date with your vaccinations and consider getting tested before you travel as well as upon returning.
All vaccines go through three clinical trial phases before they can be approved for use in the population. The trial phases ensure the safety and capacity of the vaccine to protect against the disease (i.e., its efficacy). Also, the clinical trials provide answers to other questions, such as the population groups to whom the vaccine can be administrated, the number of doses needed, and the interval required between doses.
WHO reviews the clinical trial data for each candidate COVID-19 vaccine. In addition to the safety data, WHO reviews the efficacy information (i.e., how well the vaccine works to prevent COVID-19). At this time, WHO will consider vaccines that have an efficacy rate of 70% or more in preventing symptomatic COVID-19 disease – that is, among all vaccinated persons, 70% or more will not develop symptoms of COVID-19 disease if they become infected.
For more information, please see WHO's Target Product Profiles for COVID-19 Vaccines.
Ensuring the safety of the product is the main goal of clinical trials for any vaccine or therapeutic drug. When a trial participant experiences any health event after vaccination (which may or may not be related to the vaccine), the study protocol requires an investigation to understand the cause of the event. While the researchers investigate what happened, the trial may be suspended temporarily to avoid any new events.
Vaccine safety continues to be monitored even after a vaccine starts to be used in the general population. If one or more health events are reported after vaccination, and the initial investigation reports any concerns with the safety of the vaccine, administration of this vaccine may be suspended until further information can be collected and analyzed. This is a standard procedure that can affect any vaccine – not just COVID-19 vaccines. Vaccine administration is resumed as soon as all analyses report that the vaccine is safe for use.
Before any vaccine is approved to be used in the general population, it must go through three clinical trial phases. The vaccines that are being developed against COVID-19 are following the same rigorous phases. At each phase, vaccine safety is assessed, and the trail will not proceed until all safety requirements are met. During the last two phases, researchers assess how well the vaccine protects persons from COVID-19 (i.e., its efficacy). In some cases, the phases may overlap or be sped up when sufficient data, particularly on safety, become available. Once a COVID-19 vaccine is approved for use in the general population, monitoring on safety and effectiveness continues.
In the case of COVID-19 vaccines, the administration / bureaucratic process was sped up to ensure that life-saving vaccines could reach the general public as soon as possible. The evaluation of the vaccine’s safety and efficacy met all criteria of a rigorous evaluation, and this process was never sped up to meet deadlines.
Yes, vaccine safety is always the top priority for WHO and for national regulatory agencies. All vaccines go through rigorous clinical trial phases before they are approved for use in the general population. These trials aim to ensure the safety and ability of the vaccine to protect against the disease.
The vaccines against COVID-19 follow these same strict requirements for safety and efficacy. They will not be recommended, approved or introduced in countries until their safety has been proven to national regulatory agencies. After COVID-19 vaccines are approved, monitoring for safety continues. This monitoring is a normal part of immunization programs and is done for all vaccines.
More information: Safety of COVID-19 vaccines
Yes, mRNA vaccines are held to the same rigorous safety standards as all other vaccines. Vaccines are not approved or rolled out for use in the general population until all safety data have been thoroughly reviewed by national regulatory authorities.
More information: Safety of COVID-19 vaccines
With PAHO’s support, countries in the Americas developed regional surveillance systems to identify and respond quickly to any Events Supposedly Attributable to Vaccination or Immunization (ESAVI). The goal of this surveillance network is to allow Ministries of Health to investigate any adverse event following vaccination (regardless of whether it is associated with the vaccine). This is a routine step that all countries take when introducing any new vaccines to their population.
After receiving the vaccine, your body will break down its components within a few days and that will be left is your body’s memory on how to fight the virus. Side effects to vaccines usually happen within the first few days of receiving the shot, and are generally mild (ex., headache, malaise, pain at the site of injection). If the side effect lasts more than 10 days, it is recommended that you consult your healthcare provider. More serious or long-lasting side effects to COVID-19 vaccines are extremely rare. If you experience difficulty breathing, chest pain, confusion, loss of speech or mobility after your vaccine, contact your healthcare provider immediately.
More information: Side effects of COVID-19 vaccines
Thrombosis with Thrombocytopenia Syndrome (TTS) is a condition where a person presents with both severe venous or arterial thrombosis (confirmed through imaging, surgical, or pathology tests) and new onset thrombocytopenia (platelet count of fewer than 150,000/μL). This is an extremely rare event that may occur after vaccination with the AstraZeneca or Janssen COVID-19 vaccines.
WHO concluded that the benefit of vaccination in protecting against COVID-19 far outweighs the risks of developing TTS, since the condition is rare and can be easily treated if the person seeks care early. Nonetheless, people who have had blood clots associated with TTS after their first vaccine dose should not be given their second dose with the same COVID-19 vaccine.
More information can be found here.
mRNA vaccines are used to protect millions of people against COVID-19. Data are available from both clinical trials and country surveillance programmes on their effectiveness and safety. In some persons, mild side effects are expected for 1-2 days after vaccination. These are a normal sign that the body is developing protection.
There have been rare reports of cases of myocarditis (i.e., inflammation of the heart muscle) and pericarditis (i.e., inflammation of the membrane surrounding the heart) following a dose of mRNA COVID-19 vaccine (i.e., Pfizer or Moderna). The symptoms of myocarditis and pericarditis are generally mild and are easily managed if treated early. Immediate treatment with medication and rest can help avoid long-term heart damage. If you experience new and persisting chest pain, shortness of breath or have a racing or pounding heartbeat within a few days of vaccination with an mRNA vaccine, contact your doctor immediately.
Current data indicates that males aged 12-17 are at a 10-fold higher risk of myocarditis and pericarditis from the COVID-19 mRNA vaccines than females of the same age. Research is underway to understand more.
Despite the possibility of this event, WHO continues to state that the benefits of the mRNA vaccines greatly outweigh the risk of myocarditis and pericarditis, since this event is rare and is easily treatable.
Guillain-Barré Syndrome (GBS) is a rare immune system disorder that results in muscle weakness, pain or numbness and, in more severe cases, paralysis. GBS could result from different causes (including infections) and occurs more frequently in males and persons aged 50 or older. Rarely, cases may occur by chance immediately after vaccination.
In very rare instances, GBS symptoms have been reported in persons who received the Janssen or AstraZeneca COVID-19 vaccines. In these situations, the person should seek immediate medical attention if they develop weakness/tingling and paralysis in the extremities that may progress to other parts of the body including the chest and face. Symptoms may include difficulty in walking; difficulty with facial movements; double vision or inability to move eyes; or difficulty controlling bladder or bowel functions.
Despite the possibility of this event, WHO continues to state that the benefits of the AstraZeneca and Janssen vaccines greatly outweigh the risk of GBS, since this event is so rare.
There are five high-risk priority groups who are at highest risk of becoming infected with COVID-19 or suffering from severe disease, hospitalization and death from the disease. These groups are:
These persons should protect themselves from COVID-19 vaccines by receiving all doses as soon as possible – that is, two doses of the primary series plus two additional booster doses about 4-6 months apart.
Yes, PAHO/WHO recommends that those who have had COVID-19 still get vaccinated against this disease, regardless of whether the person had no symptoms or was very ill. The vaccine further boosts the body’s immune system against COVID-19. Also, to receive immunity through the vaccine is far safer than receiving it through the disease itself, since COVID-19 can have long-term consequences on a person’s health.
If the person has symptoms at the time of vaccination, SAGE recommends postponing vaccination until the person has recovered to avoid infecting others. This recommendation is applicable to all eligible persons, including older adults.
If you have symptoms of COVID-19, or have been diagnoses with COVID-19, you can still get vaccinated. However, you need to follow the local isolation guidance before going to get vaccinated to avoid infecting others. Therefore, and it is best to wait until after your recovery to get vaccinated.
COVID-19 vaccines can be administered at any time, as long as the person is no longer infected with SARS-CoV-2 (i.e., reports no symptoms) to avoid infecting others when receiving the vaccine.
A person may wait up to 6 months to receive the next COVID-19 vaccine dose if they have been infected with COVID-19 before. During this time, the person may rely on the immunity generated by the body during the disease. However, emerging data show that people who have previously had COVID-19 may fall sick again, especially in areas where variants of concern are circulating. Therefore, WHO recommends that people receive their vaccine dose (primary series or booster) as soon as possible, regardless of whether they have been ill with COVID-19.
Only people 12 years of age and older can get COVID-19 vaccines at the same time as other core vaccines.
Children under 11 years of age should get the pediatric COVID-19 vaccine and wait 14 days or longer to receive any other vaccine.
The only exception is influenza (flu) vaccine, which can be given on the same day with other vaccines at any age.
Yes. Like all of us, pregnant women are at risk of contracting COVID-19. Because their immune systems change throughout pregnancy, they are more vulnerable to respiratory infections such as COVID-19. If they do become ill, they tend to develop more severe symptoms and their treatment may require longer hospitalization in intensive care units, greater need for ventilatory support, and a higher chance of dying when compared to non-pregnant people of the same age and ethnicity.
All pregnant women (regardless of risk factors) should receive four COVID-19 vaccine doses – that is, two doses of the primary series plus two additional booster doses about 4-6 months apart – as soon as possible.
Yes. Lactating women can get vaccinated and because they are as likely to benefit from vaccination as other adults their age, and breastfeeding offers substantial health benefits to lactating women and their breastfed children. WHO does not recommend discontinuing breastfeeding because of vaccination.
Since none of the COVID-19 vaccines are live virus vaccines, it is biologically unlikely that they would pose a risk to the breastfeeding child.
Severe COVID-19 disease, hospitalization and death has been associated with medical conditions associated such as hypertension, diabetes, asthma, and pulmonary, liver or kidney disease.
People with these underlying conditions should receive four COVID-19 vaccine doses – that is, two doses of the primary series plus two additional booster doses about 4-6 months apart – as soon as possible.
Severe COVID-19 disease, hospitalization and death has been associated with immunodeficiency conditions.
People with depressed immune systems should receive four COVID-19 vaccine doses – that is, two doses of the primary series plus two additional booster doses about 4-6 months apart – as soon as possible. Since none of the COVID-19 vaccines are live virus vaccines, it is biologically unlikely that they would pose a risk to the person.
GBS is a rare immune system disorder that results in muscle weakness, pain or numbness and, in more severe cases, paralysis. GBS could result from different causes, including infections, and occurs more frequently in males and persons over 50 years old. Cases may occur by chance immediately following vaccination.
Yes, people who had GBS previously may receive a COVID-19 vaccine. To date, no cases of GBS have been reported following vaccination in participants in the mRNA COVID-19 vaccine clinical trials.
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Children as young as 6 months old can be vaccinated against COVID-19, using the paediatric version of the Pfizer or Moderna vaccines. All other vaccines are for persons aged 18 years or older.
PAHO/WHO recommends peoples at higher risk of infection, hospitalization or death from COVID-19 receive all doses of the COVID-19 vaccine – that is two doses of the primary series plus two additional booster doses about 4-6 months apart – as soon as possible. This category includes children and adolescents younger than 18 years with comorbidities that increase their risk of severe illness, hospitalization and death from COVID-19.
WHO does not recommend that healthy children younger than 12 years receive a booster dose.
Children report fewer symptoms and fewer instances of severe disease and death from COVID-19 compared to adults. Nonetheless, childhood vaccination is essential to reduce the transmission of the SARS-CoV-2 virus (which causes COVID-19) in the general population and among high-risk priority groups (e.g., health workers, the elderly, pregnant women, immunocompromised persons or persons with comorbidities).
The implementation of public health measures (e.g., use of a mask, social distancing, hand washing) should continue in all settings where the risk of viral transmission is high, especially in closed environments or poorly ventilated places. Read more information about this here.
If a person suffers from allergies that are not related to a component of the COVID-19 vaccine he/she will receive, the vaccine can be administered.
A person with a history of anaphylaxis to any other injectable vaccine or therapy (i.e., intramuscular, intravenous, or subcutaneous vaccines or therapies) can still be vaccinated against COVID-19. Nonetheless, a health professional should conduct a risk assessment before vaccination. Also, these persons should be observed for 30 minutes after vaccination in healthcare settings where anaphylaxis can be treated immediately.
People with an immediate non-anaphylactic allergic reaction to the first dose (i.e., hives, angioedema without respiratory signs or symptoms occurring within 4 hours of administration) should not receive additional doses of the same COVID-19 vaccine. If a second dose of the same vaccine is administered, the patient should be observed closely for 30 minutes after vaccination in a healthcare setting where severe allergic reactions can be treated immediately.
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Yes. COVID-19 vaccines protect you from getting severely sick or dying from COVID-19 by teaching your body how to fight off the SARS-CoV-2 virus (which causes COVID-19). However, a vaccine may not protect you well against infection with the SARS-COV-2 virus – although the disease tends to be mild or asymptomatic. To further limit the risk of infection, continue to implement social distancing, mask wearing and hand washing in closed environments, poorly ventilated settings or when in contact with a person who shows symptoms of COVID-19.
Some people can experience mild side effects, such as soreness at the injection site, muscle aches, or a fever, but these disappear in a few days. These side effects are a result of your immune system responding to the vaccine and are not a sign that you are sick with COVID-19. The vaccines against COVID-19 will not make you sick or contagious with COVID-19.
Yes. Even if you don’t experience any of the common side effects after getting vaccinated (e.g., sore arm, fatigue, headache, chills, muscle ache, fever), it does not mean that the COVID-19 vaccine did not generate protection. All COVID-19 vaccines have been proven to be safe and effective.
Yes. Some of the approved vaccines require that people get a second shot within a certain period of time. Getting this second shot when recommended strengthens your body’s immune response to the virus. Failing to get the second dose means you will not be optimally protected from the disease.
A booster dose is an additional dose given to a person who completed a primary vaccination series (i.e., first two doses) once the vaccine’s effectiveness (i.e., its ability to protect the person from COVID-19) has fallen below acceptable levels.
WHO recommends that booster doses be administered 4-6 months after the last COVID-19 vaccine dose. If more than 6 months have passed, the person should receive a booster dose as soon as possible.
Persons who belong to one of the five high-risk priority groups (i.e., health workers; the elderly (aged 60 years or older); persons with comorbidities; immunocompromised persons; pregnant women) should receive a total of four doses of COVID-19 vaccine – that is, two doses of the primary series plus two additional booster doses about 4-6 months apart.
WHO does not recommend that children and adolescents younger than 18 receive any booster doses, since there is insufficient evidence available on their safety and effectiveness in the pediatric population.
Yes. Research has shown that people who received booster vaccines were far less likely to test positive than those who had only received two doses. Additional studies have shown that in December 2021, as the Omicron variant emerged, unvaccinated persons reported a three-fold risk of COVID-19 infection compared to fully vaccinated adults, and a five-fold risk compared to adults who received a booster.
Read more about this here.
It is safe and effective for you to receive a second or a third dose of a different COVID-19 vaccine. If you’re offered a different type of vaccine, you can go ahead and get vaccinated. WHO considers two doses of any WHO EUL vaccine to be a complete primary series. See the full list of COVID-19 vaccines with WHO EUL here.
By mixing and matching vaccines, countries are able to maximise vaccine impact in the event of constrained or limited supply.
People over 60 who have received two doses of Sinovac and Sinopharm should be given a third dose to restore waning immunity over time.
Read more about this here.
Yes. Even after getting vaccinated, keep taking precautions to protect yourself, family and friends if there are still COVID-19 cases reported in your area.
The maximum level of protection is reached two weeks after you receive the second dose of vaccine. This means that you don’t get full immunity until 2–4 weeks after the second dose.
COVID-19 vaccines are highly effective, but a small percentage of people will still get ill from COVID-19 after vaccination (this is known as a breakthrough infection). Also, there is a chance that you could pass the virus on to others who are not vaccinated. Some people have not been vaccinated against COVID-19, cannot be vaccinated, or do not develop full immunity in response to COVID-19 vaccines because of a weakened immune system. Continue to practice all public health measures to protect yourself and others: Avoid poorly ventilated places or wear a mask, wash your hands frequently, maintain distances of 1 meter or more, stay home if unwell and get tested, stay informed about how many COVID-19 cases are reported in your area, and get vaccinated as soon as possible).
Read more about this here.
As of September 2022, researchers are still studying how long immunity (protection) from the COVID-19 vaccines lasts, and how well the vaccines protect against different variants of the SARS-CoV-2 virus. As more studies are completed, WHO will be able to determine whether additional vaccination doses are necessary and how frequently.
Yes. You can donate blood immediately after receiving the COVID-19 vaccine.
No. Although the ingredients on vaccine labels may sound alarming (e.g., thiomersal, aluminum, formaldehyde), these substances are generally found naturally in the human body, in the food we eat, and in the environment around us. The amounts contained in vaccines are extremely small and will not harm the body.
No, the COVID-19 vaccine produced by AstraZeneca does not include sulfur in any amount.
No. the COVID-19 vaccines cannot and will not make you magnetic, not even at the site of the injection. The vaccines are free from metals that would cause a magnetic attraction to your body.
No. Vaccines build immunity without the damaging effects that the COVID-19 illness may have, including long-term effects and death. Allowing the disease to spread could cause millions of deaths and even more people living with the long-term effects of the virus.
Vaccines do not contain fetal cells.
In the production process of some vaccines, cell lines have been used that originated from cells recovered from fetal tissue obtained from abortions performed in Sweden and England more than 40 years ago. These abortions were voluntary, they complied with the countries’ legislation and were not performed with the aim of generating cell lines to produce vaccines.
Cell lines revolutionized scientific research by allowing the study in laboratory of various biological processes that could occur in some living organisms. Cell lines are generated using cells obtained from tissues (human, animal or plant) and cultured in a laboratory, for example, to investigate new drugs or vaccines. Various types of cell lines have been used in the production of vaccines, such as those for rubella, chickenpox, hepatitis A, rabies and recently, in some of the vaccines against COVID-19.
Cell lines are used by scientists because viruses, unlike bacteria, need cells to grow and multiply. Cell lines are necessary for viruses to grow and multiply so they can be studied in the laboratory. Cell lines developed from fetal tissue have the advantage that they can grow and multiply indefinitely under certain laboratory conditions, because fetal cells are in a process of continuous differentiation and growth. This makes them preferable for research over other cell lines or primary cell cultures that can only reproduce a limited number of times.
While some vaccines use cell lines in their research and production process, no vaccine contains fetal cells.
No, none of the approved COVID-19 vaccines will cause you to release, discharge or shed any of the vaccine components.
No. The effectiveness or safety of the vaccine is not impacted by any food or drink consumed before or after taking the COVID-19 vaccine.
People can receive the COVID-19 vaccine at any point during their menstrual period.
There have been some reports of people experiencing disruption to their menstrual cycle after being vaccinated against COVID-19. There is not yet enough data available to know whether there is a connection between the vaccines and this disruption. Several large studies researching the impact of vaccines on menstrual cycles are ongoing.
If you have concerns or questions about your periods, do not hesitate to speak with a health care provider.
No. If a person has been vaccinated against COVID-19, it will not have any effect on another person´s menstrual period.
No, studies of authorized vaccines have shown that receiving COVID-19 does not have any effect on fertility. In fact, some participants in the clinical studies got pregnant during the studies. No vaccines suspected of impacting a person’s ability to conceive have ever been or will be approved.
No. WHO and national regulatory agencies have never approved any vaccine suspected of causing breast cancer, or any other type of cancer. People who received a COVID-19 vaccine can have swelling in the lymph nodes (lymphadenopathy) in the underarm near where they got the shot. This swelling is a normal sign that your body is building protection against COVID-19. However, it is possible that this swelling could cause a false reading on a mammogram. Some experts recommend getting your mammogram before being vaccinated or waiting 4 to 6 weeks after getting your vaccine.
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No. COVID-19 vaccines do not increase breast size. Some people who receive the COVID-19 vaccine may have swollen lymph nodes under the arm where the shot was given. However, this happens with all vaccines, not just the COVID-19 vaccine.
This information on swollen lymph nodes is reported by the American Cancer Society.
No. COVID-19 vaccines do not cause Monkeypox. Monkeypox is a viral zoonotic disease caused by the monkeypox virus and is transmitted from person to person mainly through direct or indirect contact with the rash, bodily fluids (e.g., fluid, pus or blood from skin lesions). Scabs are particularly infectious. Clothing, bedding, towels, or objects like eating utensils/dishes that have been contaminated with the virus from contact with an infected person can also infect others.
In May 2022, several countries where monkeypox is not endemic reported cases, including some countries in the Americas. On 23 July 2022, the WHO Director-General declared the multi-country outbreak of monkeypox constitutes a Public Health Emergency of International Concern (PHEIC). Visit our monkeypox outbreak site to stay up-to-date with the situation in the Region of the Americas.