Information about the novel coronavirus (the virus that causes COVID-19) is constantly evolving. We will refresh our novel coronavirus content periodically based on newly published peer-reviewed findings to which we have access. For the most reliable and up-to-date information, please visit the CDC website or the WHO’s advice for the public.
Millions of doses of coronavirus disease 2019 (COVID-19) vaccines have been given to adults in the United States, and data so far indicates these vaccines are indeed safe.
The U.S. Food and Drug Administration (FDA) gave Emergency Use Authorization (EUA) to three vaccines from 2020-2021. These three vaccines are the Moderna vaccine, the Pfizer-BioNTech vaccine, and the Johnson & Johnson (Janssen) vaccine (CDC, 2021a). The vaccines underwent clinical trials involving tens of thousands of people, and after careful consideration, the FDA approved EUAs for the vaccines. The first of the vaccines to get full FDA approval for use against COVID-19 is the Pfizer-BioNTech vaccine in 2021 (FDA, 2021c).
But it doesn’t stop there. Scientists at the Centers for Disease Control and Prevention (CDC) continue to keep track of any adverse effects people experience after getting the vaccine. There is also a voluntary tracker, called v-safe, that you can use to tell the CDC about any side effects (CDC, 2021b). Here’s more about the vaccines, how effective each is, and any potential side effects to watch out for.
- With millions of doses administered nationwide, the COVID-19 vaccines have so far been shown to be safe and effective. The most common side effects of the vaccines are mild and include injection site soreness, headaches, and fatigue. You cannot get sick with COVID-19 from the vaccine. The risks of severe allergic reactions and severe adverse reactions are very small.
How do the COVID-19 vaccines work?
The goal of the vaccines is to train your immune system to recognize the COVID-19 virus as quickly and efficiently as possible without you getting sick.
The vaccines contain blueprints of genetic material that code for specific spike proteins that exist on the outside of the coronavirus. These spike proteins are also what give the virus its signature crown shape. The COVID-19 vaccines then deliver these blueprints to your cells, where protein factories start to build the viral spike proteins. The vaccine itself doesn’t contain the code for any other part of the virus—just the spike proteins.
Once your cells create the viral proteins, your immune system mounts an immune response in the form of antibodies. Antibodies can be stored for future use so if you come into contact with the coronavirus, your immune system can use them to fight off the infection before you get sick.
The Pfizer and Moderna vaccines require an initial two doses to be effective. After you receive both doses, it can take 1–2 weeks (depending on which vaccine you get) until you gain protection against COVID-19. Studies have shown that both vaccines are very effective at protecting you from COVID-19, with the Moderna vaccine 94.5% effective and the Pfizer-BioNTech 95% effective (FDA, 2020a; FDA, 2020b). Studies have shown that the Janssen vaccine, which requires an initial single dose, also offers good COVID-19 protection and is 66.9% effective (FDA, 2021d).
Side effects of the COVID-19 vaccines
So far, the most common side effects of the available vaccines are similar. Here are some common side effects people experience (CDC, 2021c):
These side effects can occur after any dose of the vaccine. People who get one of the two-dose vaccines often report more side effects after the second dose.
It’s important to note that these effects are not signs that you have COVID-19. Rather, they are proof your immune system is working against the virus. That being said, you can catch COVID-19 right after getting the vaccine as it takes weeks for your body to develop full protection—especially if your body hasn’t had enough time to build up immunity.
Severe allergic reactions
Rarely, vaccines can cause severe allergic reactions (also called anaphylaxis), which can occur with any vaccine or medication.
The CDC reports that the risk of anaphylaxis after the currently available COVID vaccines is two to five cases per million doses given. To put that in perspective, you have less than a 0.0005% chance of having a severe allergic reaction to the vaccine (CDC, 2021f). It’s so rare that you’re more likely to get sick from COVID-19 than have a severe allergic reaction (CDC, 2021e).
Data has also found that 80% of people who experienced adverse reactions had a history of allergies or allergic reactions to drugs and foods in the past. Furthermore, 90% of anaphylaxis reactions occurred within 30 minutes of getting the vaccine (CDC, 2021c). So, if you’ve had an allergic reaction to something unrelated to vaccines or injectable therapies, then there’s no reason not to get a COVID-19 vaccine.
In addition, those with allergies to things like food, pets, and environmental allergies don’t need to take special precautions before getting the vaccine. However, if you have a history of severe allergic reactions, you’ll likely be monitored for 30 minutes after getting the vaccine to watch for any concerning side effects (CDC, 2021d).
Symptoms of anaphylaxis include trouble breathing, difficulty swallowing, hives, swelling of your mouth or throat, and widespread skin rash. If you think you might be having a severe allergic reaction to the vaccine, you should call 911.
Serious adverse effects
There are rare examples of other serious adverse effects after getting a COVID vaccine.
Heart problems such as myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) occurred in some people who received Pfizer and Moderna vaccines, and blood clots occurred in some people who received the Janssen vaccine (CDC, 2021g; CDC, 2021h). You have a much higher risk of getting sick with COVID-19 than you do of having any serious adverse effect. If you have any concerns or any medical history of clots, you can speak to a health care provider to discuss which vaccine is your best option.
Can you get COVID-19 from the vaccine?
To put it simply: the vaccines do not give you COVID-19.
None of the COVID-19 vaccines in use today contain live viruses, so they can’t make you sick. The only thing the vaccines carry from COVID-19 virus are blueprints of genetic material needed to create spike proteins. This trains your immune system to recognize the virus should you become exposed in the future. To get COVID-19, you would need the entire virus particle to reproduce itself in your body, and the vaccines don’t carry whole virus particles.
It’s common to experience side effects after receiving the vaccine, including soreness at the injection site (usually in your arm), headaches, and fatigue. But these are not signs of COVID-19—it just means your immune system is responding to the vaccine.
Scientists don’t know yet if people who’ve received a vaccine can still carry the virus and transmit it to others unknowingly. That’s why it’s important to continue to still wear a face mask, avoid large gatherings, practice social distancing, and wash your hands frequently to decrease the likelihood of spreading the virus.
Pregnancy and breastfeeding safety
None of the vaccines currently available have definitively studied vaccine safety in pregnant women. In fact, the clinical trial specifically excluded pregnant people from enrolling. During clinical trials of the Moderna and Pfizer-BioNTech vaccines, some participants became pregnant, however, no pregnancy-related side effects were reported.
That being said, overall pregnancy risks and outcomes are unknown and more research is needed in this area (FDA, 2020a; FDA, 2020b). It’s also essential to remember that pregnant people with COVID-19 are more at risk for severe symptoms or even death compared to those who are not pregnant. They may also be at risk for other bad outcomes, such as delivering the baby too early or having a miscarriage (Wastnedge, 2020). Most experts do not believe the vaccines pose a significant threat to pregnant people because it doesn’t actually contain the live virus, and what viral genetic material does enter your system gets broken down by your cells.
If you’re in one of the groups being recommended for the vaccine (like healthcare workers and those who are pregnant) you should speak with a healthcare provider beforehand about the risks and benefits of getting the vaccine. The CDC is not currently recommending pregnancy tests before vaccination, nor is it advising people to avoid getting pregnant after getting the vaccine (CDC, 2021d).
Similarly, there have not been any studies on people who are breastfeeding. Again, because the COVID-19 vaccines don’t contain a live virus, it’s not likely to harm newborns.
COVID-19 vaccines and infertility
There is currently no data linking the vaccine to infertility.
You may have encountered false information saying that the spike proteins are similar to a protein needed for fertility. That would mean if your body forms antibodies against spike proteins, it also forms antibodies against the fertility protein, thereby causing infertility. But the two proteins are not alike enough for this to occur.
If the vaccines did cause infertility, then many women who were exposed to COVID-19 would be infertile, and so far there is no evidence to suggest that this has occurred (Pfizer, 2021). And as we noted, several people in both the Moderna and Pfizer-BioNTech vaccine trials became pregnant, making it even more unlikely that the vaccine causes infertility. However, scientists are continuing to study the effects of the COVID-19 vaccines and pregnancy (FDA, 2020a; FDA, 2020b).
- Centers for Disease Control and Prevention (CDC). (2021a, February). COVID data tracker. Retrieved on February 2, 2021 from https://covid.cdc.gov/covid-data-tracker/#datatracker-home.
- Centers for Disease Control and Prevention (CDC). (2021b, January). V-safe After Vaccination Health Tracker. Retrieved on February 2, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/vsafe.html.
- Centers for Disease Control and Prevention (CDC). (2021c, January). COVID-19 Vaccine Safety Update. Retrieved on February 2, 2021 from https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2021-01/06-COVID-Shimabukuro.pdf.
- Centers for Disease Control and Prevention (CDC). (2021d, January). Interim Clinical Considerations for Use of mRNA COVID-19 Vaccines Currently Authorized in the United States. Retrieved on February 2, 2021 from https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html.
- Centers for Disease Control and Prevention (CDC). (2021e, January) COVIDView: A Weekly Surveillance Summary of U.S COVID-19 Activity. Retrieved on February 2, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covidview/index.html.
Centers for Disease Control and Prevention (CDC). (2021f, September). Selected Adverse Events Reported after COVID-19 Vaccination. Retrieved on September 10, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/adverse-events.html
Centers for Disease Control and Prevention (CDC). (2021g, Jun). COVID-19 Myocarditis and Pericarditis Following mRNA COVID-19 Vaccination. September 10, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/myocarditis.html
Centers for Disease Control and Prevention (CDC). (2021h, Jun). COVID-19 Selected Adverse Events Reported after COVID-19 Vaccination. Retrieved September 10, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/adverse-events.html
- Pfizer. (2021, January). The Facts About Pfizer and BioNTech’s Covid-19 Vaccine. Retrieved on February 2, 2021 from https://www.pfizer.com/news/hot-topics/the_facts_about_pfizer_and_biontech_s_covid_19_vaccine.
- U.S. Food and Drug Administration (FDA) (2020a, December) Vaccines and Related Biological Products Advisory Committee Meeting – FDA Briefing Document: Moderna COVID-19 Vaccine. Retrieved on February 2, 2021 from https://www.fda.gov/media/144434/download
- U.S. Food and Drug Administration (FDA) (2020b, December) Vaccines and Related Biological Products Advisory Committee Meeting – FDA Briefing Document: Pfizer-BioNTech COVID-19 Vaccine. Retrieved on February 2, 2021 from https://www.fda.gov/media/144245/download.
U.S. Food and Drug Administration (FDA) (2021c, August 23). FDA Approves First COVID-19 Vaccine. Retrieved September 10, 2021 from https://www.fda.gov/news-events/press-announcements/fda-approves-first-covid-19-vaccine
U.S. Food and Drug Administration (FDA) (2021d, February 26). Vaccines and Related Biological Products Advisory Committee Meeting – FDA Briefing Document:Janssen Ad26.COV2.S Vaccine for the Prevention of COVID-19. Retrieved September 10, 2021, from https://www.fda.gov/media/146217/download
- Wastnedge, E., Reynolds, R. M., van Boeckel, S. R., Stock, S. J., Denison, F. C., Maybin, J. A., & Critchley, H. (2021). Pregnancy and COVID-19. Physiological reviews, 101(1), 303–318. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7686875/