top of page




Is the COVID-19 vaccine safe?

Covid vaccine safe

The vaccines against COVID-19 that have been authorized for use in the population are safe. So far, none of the vaccine trials (read more about how clinical trials work) have reported any serious safety concerns, like changing fertility, causing neurological problems, causing new infections, or death. Vaccine safety has been carefully monitored by both governmental and independent safety boards throughout the world.

The data from these large clinical trials make it clear that the benefits of the vaccines outweigh the harms of coming down with COVID-19.
It is also important to note that safe does not mean there are no side effects. A vaccine (like many other drugs) is considered safe when it does not cause serious adverse events. The most common side effects are pain and swelling on the arm where you got the shot. Some cases of allergic reactions have been reported, but they are extremely rare (1 in 300,000 approx.). There have also been reported cases of rare blood clotting conditions after use of the vaccines produced by AstraZeneca and Johnson & Johnson. Read more about this in this article. 

Vaccine safety has been fully proven in individuals over 16 or 18 years old (depending on the brand). 

More information: COVID-19 complications vs. vaccine side effects, Complete list of the vaccine´s ingredients

What are the side effects of the vaccines?

Can vaccine cause covid

The most common side effects are pain and swelling on the arm where you got the shot. Throughout the rest of your body, you could feel fever, chills, tiredness, and/or a headache. These effects usually last for 1-3 days.

These reactions to the vaccine are normal, and they show that your immune system is working and getting ready in case of an infection. You will likely be asked to wait for 15-30 minutes after getting a COVID-19 vaccine to see if you get an immediate reaction.

Historically it has been observed that the long-term side effects of any vaccine occur within 30 to 45 days post-vaccination. The clinical Phase 3 trials for the COVID-19 vaccines lasted at least 90 days and no serious safety concerns were reported.

More information: COVID-19 complications vs. vaccine side effects

Side effects

Can the vaccine cause COVID-19?

No, the vaccine cannot cause COVID-19 because it does not contain an infectious virus (a complete, active virus able to cause an infection). The only agent that can cause COVID-19 is the virus SARS-CoV-2 (the complete and intact form).

The main component of the mRNA vaccines (Pfizer, Moderna) is mRNA, a molecule that by itself cannot cause an infection or severe disease. In the case of the viral-vector vaccines (AstraZeneca/Oxford and J&J), they are made from harmless viruses that function as carriers to bring the information of the Spike (S) protein to the cells of the immune system. There are some companies developing vaccines with the whole virus, but they are inactivated or attenuated forms of SARS-CoV-2, which means they are not able to cause illness. The subunit vaccines use pieces or fragments of the virus to trigger an immune response.

More information: Types of vaccines, Complete list of the vaccine´s ingredients, How does the mRNA vaccine work?

Are people getting sick from the COVID-19 vaccine?

getting sick from vaccine

The COVID-19 vaccines that have been authorized for use in the general population are safe and do not cause a severe illness of any type. During the clinical trials (read more about how clinical trials work), no serious safety concerns were reported. For example, there were no reports of changing fertility, neurological problems, new infections, or death. No one had to be hospitalized as a consequence of being vaccinated.

After the vaccines started to be applied in the population, some cases of allergic reactions have been described, but they are extremely rare (1 in 300,000 approx.) and are treatable. People with a history of allergic reactions are required to wait in the medical facility for at least 30 min in case an allergic reaction occurs. That way they can get accurate treatment right away.

More information: COVID-19 complications vs. vaccine side effects

Can the vaccine give me HIV/AIDS?


No, because the COVID-19 vaccine does not contain infectious viruses of any type. HIV/AIDS is a serious disease caused by the human immunodeficiency virus (HIV). The only agent that can cause AIDS is HIV.

This concern arises from an Australian COVID-19 vaccine trial from the University of Queensland, where some trial participants had a false-positive HIV result. The tested vaccine contained a small protein fragment from HIV, which posed no risk to human health. However, the participants generated antibodies against this fragment, resulting in false-positive tests. The trial was abandoned. 

More information: complete list of the vaccine´s ingredients, How does the mRNA vaccine work?


Does the vaccine cause women to go infertile?

The vaccines against COVID-19 that have been approved for use in the population are safe and do not cause any change in fertility in women or men. During the vaccine trials (read more about how clinical trials work), there were no reports of alterations in fertility or any other serious consequence in the participants. These parameters were carefully monitored by both governmental and independent safety boards throughout the world.

Can you safely get a COVID-19 vaccine if you have a history of allergic reactions?

allergic reaction

People with a history of severe allergic reactions to any ingredients in any COVID-19 vaccine are urged not to get the vaccine (see for complete list of the vaccine´s ingredients). 

For those with a history of severe allergic reactions not related to vaccine ingredients, vaccination is recommended but with proper safety measures taken (presence of a medical professional with access to epinephrine or antihistamines).

The cases of severe allergic reactions that have been reported are extremely rare (1 in 300,000 approx.) and the cause is still to be determined. All persons affected were treated and are doing fine.

The mRNA vaccines (Moderna and Pfizer) do not contain common allergens, like eggs or metals. However, the Pfizer and the Moderna mRNA vaccines do contain polyethylene glycol (PEG), an ingredient that can sometimes cause allergic reactions.

More information: COVID-19 complications vs. vaccine side effects



Who can receive the COVID-19 vaccine?

who can receive

The COVID-19 vaccine has been authorized for individuals above 16 or 18 years, depending on the brand (Pfizer - 16 years or older, Moderna and Astrazeneca/Oxford - 18 years or older).  

Each country has its own list of priority groups and order in which the vaccines will be applied to the population. For more details, check the official publications of the health authorities from your country and region. 

Can the vaccines be used in children and young people?


COVID-19 vaccines have not been approved yet for use in persons under 16 or 18 years, depending on the brand of vaccine. Since this group was not included in the clinical trials that already took place (read more about how clinical trials work), there is not enough safety data to recommend vaccination in children. Excluding this group from clinical trials is a common practice because children, pregnant, or breastfeeding people are considered vulnerable populations. First, it is necessary to make sure that the vaccine is effective in adults before testing it on them.

Now that we know that the COVID-19 vaccines are safe for people over 16 years, vaccine sponsors have already started or are going to start trials for children by age group. Pfizer began in October 2020 testing the vaccine in children aged 12-15. Moderna started in December 2020 and AstraZeneca is starting in February 2021. For children between 5 and 11 years, the trials will start in April 2021. For the youngest ones (<5 years), the tests will begin in 2022.

Although the incidence of severe COVID-19 is low in children (they mainly remain asymptomatic), it is very important for them to be vaccinated because herd immunity needs to be developed in the population and kids are part of the transmission chain.

Can pregnant women be vaccinated?


There is limited data regarding the safety of the COVID-19 vaccines in pregnant or breastfeeding people. In this group, the application of the vaccine must be weighed against the established benefits together with a medical doctor.

What is known so far about vaccine safety is that individuals who got pregnant during vaccine trials had no complications from the vaccine (read more about how clinical trials work). Before the clinical trials were done, while still testing the vaccine in animal experiments, pregnant rats were injected with the vaccine and they did not present any adverse effects (fetal or postnatal development).

It is important to emphasize that pregnant individuals are at higher risk for COVID-19 complications. Hence, different organizations like the CDC, FDA, and the American College of Obstetricians and Gynecologists (ACOG), recommend vaccination for pregnant and breastfeeding individuals. mRNA vaccines (Moderna and Pfizer) are mostly recommended because the mRNA molecule degrades shortly post-injection, meaning that it will not reach the baby. Inactivated virus vaccines are not advised for this group.

More information: How do mRNA vaccines work?

Can the vaccine be used in people with an immuno-compromised condition?


Immuno-compromised people were not specifically tested in the clinical trials that already took place due to concerns about efficacy. In consequence, there is not a lot of information about how the vaccine works in this population.

A small group of immune-compromised persons living with HIV was included in the Pfizer clinical trial (120 people) and in the Moderna trial (176 people). In both cases, no safety concerns were reported. Therefore, immuno-compromised people are advised to get vaccinated after consulting with their medical doctor.

A decreased effect of the vaccine could be expected in this population, but that remains to be tested. 



Why do I have to still wear a mask if the vaccine is so effective?


The vaccines are very effective in preventing serious COVID-19 while being safe. However, having COVID-19 is not the same as being infected with SARS-CoV-2. Some people (the famous asymptomatic) are infected but show no symptoms or develop a disease. At this moment, it is still not known whether the COVID-19 vaccine prevents both infection and disease, or just the latter. In other words, there is a possibility that a vaccinated person remains asymptomatic but is still infected with SARS-CoV-2 and spreads the virus to others without being aware of it.

That is why we strongly advise to keep on wearing a mask after receiving the vaccine, because vaccinated people may still be part of the transmission chain.

Besides, wearing a mask is a gesture of solidarity with those who cannot get vaccinated yet, like children, those with severe allergic reactions, and some pregnant individuals. 

I read in the news that a nurse who got vaccinated still got infected, how is this possible?  


This has to do with the time it takes for the immune response to build up a reaction against the virus. Once you are injected with the vaccine, your immune system starts building up a response, just like it would when you get infected with the virus. The difference is that the vaccine does not cause you to become sick, while the virus does. As described here, generally it takes 10-14 days for the body to develop the immune reaction. In the case of these vaccines, the reaction can still be a bit too weak, that is why you get two shots, in which the second one functions as a booster to further train your immune system.


Therefore, only 14 days after the second dose you can expect the full protection of the vaccine. 

The nurse referred to in the question got sick a couple of days after the first vaccine, which means they were not immune and protected yet, as not enough time had passed.



Are there cells from aborted fetuses in the vaccine?


None of the COVID-19 vaccines, or any other vaccines, contain human fetal cells obtained from an abortion. Cells are not added to a vaccine (see also post on the ingredients of the vaccines).

The confusion about this topic comes from the use of the cell line HEK293 in virus research. A cell line is a cell that can be grown in the lab continuously, sometimes indefinitely. These types of cells are used commonly in biological and medical research. Such cells make it possible to perform research on human cells and test drugs, for instance, without having to give it to a person. This allows researchers to test what is safe and effective before giving any new drug to a patient. 

There are many different cell lines in use, and one of them is HEK293. All cell lines are derived from an original human sample, for instance, a cancer cell that is obtained after a surgeon has removed a tumor from a patient. HEK293 was established in the 1970s from an aborted fetus in the Netherlands. This was an elective and legal abortion by Dutch Law. In the lab, the cells were transformed with adenovirus. The addition of adenovirus genes to the cells allows the cells to produce high levels of protein. The original cells have been multiplied and changed in the lab for many years. The currently used cell lines in research labs are not original cells from fetal tissue.

Pfizer and Moderna did not use these cells to develop COVID-19 vaccines. However, they did use the cell line to test whether the vaccine was working before giving it to people. This was done to test the efficacy and ensure safety before starting clinical trials with the vaccines.

Is there a microchip in the COVID-19 vaccine?


No, there is no microchip in any of the vaccines. The content of the vaccines is thoroughly checked by governmental and independent regulators during the clinical trials (read more about how clinical trials work).

More information: complete list of the vaccine´s ingredients



Who gets the vaccine first?


This is determined by the policy of each country, state, province or district, and therefore difficult to answer. Generally, public health officers tend to give priority to those that are frontline workers directly working with COVID-19 patients, such as doctors and nurses at ICU departments, and to people who are at the greatest risk of severe disease and risk of death from the disease. In the case of COVID-19 that is elderly people and those with other diseases. Once more vaccines become available, everyone will get access to the vaccines, but that will take time as a vaccine needs to be created, distributed, and given by a health care professional for every single person on earth.

How are they going to inject the vaccine at -70°C?


Some of the vaccines require storage at -20°C or -70°C. This is due to the properties of the vaccine ingredients. To ensure their efficacy storage at these temperatures is required. However, vaccines will be thawed and prepared for injection at room temperature and you will receive the vaccine at room temperature. The short time at a higher temperature does not affect the efficacy of the vaccines.

Is handwashing actually important? Is surface transmission a way that SARS-CoV-2 is spreading?


This is an excellent question. In brief: yes, handwashing is important as a measure to prevent SARS-CoV-2 infection and spread. However, the virus has more than one route of transmission, which in practical terms means that you have to take more than one measure to stop it. 


SARS-CoV-2 spreads from an infected to a not-infected person via 1) aerosols, 2) saliva droplets that contain virus, and 3) surfaces (fomites). When a person is infected, he or she produces viruses in the nose and mouth. When the person coughs, sneezes, speaks, sings or breathes (mainly heavily breathing), viral particles are present in the released saliva droplets (the small ones are called aerosoles, the bigger ones are called respiratory droplets). These saliva particles containing virus can spread all over the place and can get access to the mouth, nose or eyes of a person in the surrounding area. Additionally, the saliva particles produced by an infected person can fall and remain on different objects, such as tables and doorknobs. In this case, other people can get infected when touching these surfaces and then touching their eyes, noses or mouths without cleaning their hands first. 


Which of these transmission routes is more important? Current evidence suggests that aerosol transmission and respiratory droplets are the main routes of contagion. However, surface transmission can still happen. So, do not forget the golden combo: masks, safe distance and hand hygiene!

bottom of page