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Health Guide / COVID-19

What are the side effects of the COVID-19 vaccine?

Mike Bohl, MD, MPH, ALMchimene richa

Reviewed by Mike Bohl, MD, MPH, ALM, written by Chimene Richa, MD

Last updated: Sep 10, 2021
6 min read

table of contents

  1. How do the COVID-19 vaccines work?
  2. Common side effects of the COVID-19 vaccine
  3. Severe allergic reactions
  4. Serious adverse events
  5. Myths about side effects

Important

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.

Covid vaccines are widely available, and though no vaccine is 100% effective, clinical trials and ongoing research show that the available vaccines are very effective at preventing severe COVID-19, the need for hospitalization, and death, and preventing the spread of infection to others (CDC, 2021f). 

Available vaccines can even be effective at preventing severe disease and death in new virus variants that arise (CDC, 2021g). Since their approval, millions of Americans have safely received the COVID-19 vaccine and over 500 million doses have been given worldwide (CDC, 2021a). 

The most common side effects of the COVID-19 vaccines include pain at the injection site, fatigue, and headaches. In very rare cases, a person can have a severe allergic reaction to the vaccine. Most anaphylactic reactions occur within 30 minutes of getting the vaccine. The vaccine does not cause COVID-19 illness, infertility, or changes in your DNA, and the bottom line is that the benefits of the COVID vaccines currently available far outweigh any risks. 

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How do the COVID-19 vaccines work?

The vaccines work by training your body’s immune system to recognize the coronavirus and make antibodies to fight it so you won’t become sick with COVID-19. If you want to get into the nitty gritty of how it works, the mRNA vaccines that are most widely distributed in the US (like those created by Pfizer and Moderna) work by delivering a little piece of mRNA (kind of like an instruction manual) that codes for the little spikes on the outside of the virus right into your cells. 

Your cells can then use these instructions to generate the spikes which are then released into your bloodstream. Your immune system sees these little spikes, recognizes that they’re foreign, and generates a little army of white blood cells to be armed and ready should you be exposed to the real deal. 

Common side effects of the COVID-19 vaccine

The coronavirus vaccine can cause mild side effects. Most of these side effects are the result of your immune system responding to the vaccine and preparing your body to prevent infection should you be exposed to the virus in the future.

Most of the side effects of the coronavirus vaccine are minor and resolve within a few days. Some people don’t experience any side effects at all, and some only have side effects after the second dose. Common side effects include (CDC, 2021b):

Some of these side effects may make you feel sick, but they are not the same as having COVID-19. The CDC has some tips to help you feel more comfortable after your vaccine (CDC, 2021c):

  • Put a clean, cool, wet washcloth over the part of your arm where you got your vaccine
  • Move your arm around every once in a while
  • Drink plenty of fluids and dress lightly if you have a fever
  • Talk to a health care provider about taking over-the-counter medicine, such as ibuprofen or acetaminophen

Severe allergic reactions

An uncommon but potentially serious side effect of the COVID-19 vaccine is a severe allergic reaction, also called anaphylaxis. Anaphylaxis can include a variety of symptoms like trouble breathing, trouble swallowing, dizziness, low blood pressure, hives, and more.  

According to the CDC, only a small percentage of people have had anaphylaxis after getting a COVID-19 vaccine.  Within this very small group of people with severe allergic reactions, most had a history of prior allergic reactions to foods or drugs. Since most of the anaphylaxis reactions occurred shortly after getting the vaccine, you will likely be monitored after getting the vaccine to make sure that no serious reactions develop if you have a history of anaphylaxis (CDC, 2021d). 

If you think you might be having a severe allergic reaction to the vaccine, call 911.

Serious adverse events

Heart conditions

Rarely, heart conditions have occurred after receiving a COVID-19 vaccine. Myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the tissue around the heart) have occurred in patients who received COVID-19 vaccines. 

The symptoms of these conditions include shortness of breath, chest pain, and a racing heartbeat. Many of the reported cases occurred in young adults after mRNA vaccines, but they can occur in any age group. The percentage of people who experienced these events is very small in comparison to the millions of vaccines administered, and the risk of long-term effects and complications from COVID-19 disease are potentially more serious (CDC, 2021j).

Blood clots

A rare complication seen after the Johnson & Johnson vaccine is the development of blood clots. Most of the reported cases occurred in women under 50 years old. It is an uncommon adverse event that has not been seen with other available COVID-19 vaccines (CDC, 2021k). If you have a history of blood clots, let your healthcare provider know as they may decide that you should receive one of the other available vaccines.

Myths about side effects

Myth: Getting COVID-19 is a side effect of the COVID-19 vaccine

Since the COVID-19 vaccine does not contain live coronavirus, you cannot get COVID-19 from the vaccine. The vaccines only carry blueprints to make the viral proteins and not the rest of the virus. Some of the side effects of the vaccine may make you feel ill, but that does not mean that you have COVID-19. It’s just your body’s way of telling you that your immune system sees the spike proteins, and is busy mounting a defense. 

No vaccine is 100% effective and the coronavirus vaccines are no exception. They are very effective at preventing infection and especially effective at preventing serious illness, hospitalization, and death from COVID-19. That said, you can still catch and transmit the coronavirus after you have been vaccinated. Monitor your local news and keep track of outbreaks in your area. Make sure to get tested if you’ve been exposed to someone with COVID-19 and use your judgment when it comes to spending time around other people. 

Myth: Changes in your DNA are potential side effects of the COVID-19 vaccine

The COVID-19 vaccines do not change your DNA. Some vaccines carry viral mRNA. Even though it is genetic material, mRNA is different from DNA and it is unable to enter the nucleus of your cells, where the DNA is stored. The mRNA stays outside of the nucleus in the cytoplasm, where your protein-making factories exist and manufacture the viral spike proteins (CDC, 2021e). Other vaccines use a different, harmless virus that carries a DNA blueprint for the spike protein. The virus does not interact with your DNA at all (CDC, 2021h).

Myth: Infertility is a side effect of the COVID-19 vaccine

Infertility (the inability to conceive children) is not a side effect of the vaccine. This myth arose from false reports that have been shown to be incorrect (Male, 2021). In fact, we already have plenty of documentation of people who have become pregnant after receiving the vaccines (FDA 2020a; FDA 2020b). According to CDC recommendations, COVID-19 vaccines are also safe and encouraged in pregnant and breastfeeding women (CDC, 2021i).

If you have concerns about the COVID-19 vaccines, it can be overwhelming to search for information online. Speak to your healthcare professional or stick with reputable sources like the CDC (Centers for Disease Control) to get the most accurate and up-to-date information.

References

  1. Centers for Disease Control and Prevention (CDC). (2021a, February). COVID data tracker. Retrieved Feb. 4, 2021 from https://covid.cdc.gov/covid-data-tracker/#datatracker-home
  2. Centers for Disease Control and Prevention (CDC). (2021b, January). COVID-19 Vaccine Safety Update. Retrieved Feb. 4, 2021 from https://www.cdc.gov/vaccines/acip/meetings/downloads/slides-2021-01/06-COVID-Shimabukuro.pdf
  3. Centers for Disease Control and Prevention (CDC). (2021c, January). COVID-19 What to Expect after Getting a COVID-19 Vaccine. Retrieved Feb. 4, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/expect/after.html
  4. 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 Feb. 4, 2021 from https://www.cdc.gov/vaccines/covid-19/info-by-product/clinical-considerations.html
  5. Centers for Disease Control and Prevention (CDC). (2021e, March). Understanding mRNA COVID-19 Vaccines. Retrieved Aug. 16, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/facts.html
  6. Centers for Disease Control and Prevention (CDC). (2021f, May). Why CDC Measures Vaccine Effectiveness. Retrieved Aug. 16, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/effectiveness/why-measure-effectiveness.html
  7. Centers for Disease Control and Prevention (CDC). (2021g, Aug). Delta Variant: What We Know About the Science. Retrieved Aug. 16, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/variants/delta-variant.html
  8. Centers for Disease Control and Prevention (CDC). (2021h, Aug). Understanding Viral Vector Vaccines. Retrieved Aug. 16, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/recommendations/pregnancy.html
  9. Centers for Disease Control and Prevention (CDC). (2021i, Jun). COVID-19 Vaccines While Pregnant or Breastfeeding. Retrieved Aug. 16, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/viral.vectors
  10. Centers for Disease Control and Prevention (CDC). (2021j, Jun). COVID-19 Myocarditis and Pericarditis Following mRNA COVID-19 Vaccination. Retrieved Aug. 16, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/myocarditis.html
  11. Centers for Disease Control and Prevention (CDC). (2021k, Jun). COVID-19 Selected Adverse Events Reported after COVID-19 Vaccination. Retrieved Aug. 16, 2021 from https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/adverse-events.html
  12. Male, V. (2021). Are COVID-19 vaccines safe in pregnancy?. Nature reviews. Immunology, 21(4), 200–201. doi:10.1038/s41577-021-00525-y. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7927763/
  13. Pfizer. (2021, January). The Facts About Pfizer and BioNTech’s Covid-19 Vaccine. Retrieved Feb. 2, 2021 from https://www.pfizer.com/news/hot-topics/the_facts_about_pfizer_and_biontech_s_covid_19_vaccine
  14. 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 Feb. 4, 2021 from https://www.fda.gov/media/144434/download
  15. 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 Feb. 4, 2021 from https://www.fda.gov/media/144245/download
Mike Bohl, MD, MPH, ALM
Mike Bohl, MD, MPH, ALM

Dr. Mike is a licensed physician and the Director, Medical Content & Education at Ro.

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