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Last updated: Sep 10, 2021
7 min read

Are the COVID-19 vaccines safe?

yael coopermansteve silvestro

Medically Reviewed by Yael Cooperman, MD

Written by Steve Silvestro, MD


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.

There’s been a lot of controversy surrounding the COVID-19 vaccines, with many people questioning their safety and effectiveness. It’s understandable to feel a little uncertain before getting a shot in your arm, but rest assured: these vaccines are extremely safe and have been proven to be so in countless millions of people. Keep reading to learn more. 

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Is the COVID vaccine safe?

In short: yes. Millions of doses of COVID-19 vaccines have been given to adults in the United States and worldwide, and data so far indicates these vaccines are safe.  

There are three different vaccines currently available in the United States: 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 the vaccines for emergency use. Since their initial authorization, the Pfizer vaccine has received full approval (FDA, 2021c).

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 anyone can use to report side effects or adverse reactions after receiving the vaccine (CDC, 2021b). We’ve covered everything you need to know about the coronavirus 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. The risk of severe reactions is 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 your cells build these virus shell components. 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 responds by generating small particles called antibodies which can stick to virus-infected cells and neutralize them. Antibodies can be stored for future use so if you come into contact with the coronavirus after you’ve been immunized, your immune system can use them to fight off the infection before you get sick. 

The Pfizer and Moderna vaccines require at least two doses to be effective. Studies have shown that both vaccines are very effective at protecting you from COVID-19. The Moderna vaccine is 94.5% effective and the Pfizer-BioNTech 95% effective, though that immunity can wane somewhat with time (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).

What about boosters?

Because the protection from the vaccine can wane over time, a third dose is currently recommended for some people. To see the latest recommendations regarding booster doses, follow the Centers for Disease Control’s website. 

While it may seem that boosters were not part of the original plan, waning immunity is a common phenomenon when it comes to vaccines. The shingles vaccine (also known as varicella zoster) requires booster shots typically administered every 10 years. The same is true for tetanus vaccines.

Different vaccines for different strains is also a possibility down the road. This, too, is not unheard of when it comes to vaccine development. The flu vaccine is redesigned every year to mimic the circulating strains and offer the greatest possible protection against the flu virus. 

Side effects of the COVID vaccine

So far, the most common side effects of the available vaccines are similar. Here are some common side effects people experience (CDC, 2021c):

  • Injection site soreness
  • Fatigue
  • Headaches
  • Muscle aches
  • Chills 
  • Fever
  • Swelling
  • Joint pain

Overall, side effects typically pass within 24 hours after you receive the vaccine. 

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. It’s important to remember that no vaccine is 100% effective. The coronavirus vaccines that are currently available reduce the risk of infection as well as the risk of severe disease significantly. But it is still important to adhere to local guidelines when it comes to masking and social distancing. 

Severe allergic reactions to the COVID vaccine

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 to the vaccine (CDC, 2021e). 

Data also shows 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). If you have a history of anaphylaxis, discuss your risk with your healthcare provider. 

If you have seasonal allergies or a history of allergy to pet dander, for example, you 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.

Rare side effects of the COVID vaccine

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 blood clots, you can speak to a healthcare provider to discuss your options when it comes to getting vaccinated.

Can you get COVID-19 from the vaccine?

To put it simply: the vaccines do not and cannot 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 the 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.

COVID vaccine and pregnancy/breastfeeding

Currently, the CDC recommends that people who are pregnant, breastfeeding, or those that plan to become pregnant, get vaccinated against COVID-19. 

Getting COVID-19 while you’re pregnant increases the risk of preterm birth and miscarriage (Adhikari, 2020). A very large study that evaluated over 400,000 women showed that pregnancy increases the risk of requiring treatment in the intensive care unit (ICU) threefold and nearly doubles the risk of dying of COVID-19 (Zambrano, 2020). 

So far, there has been no evidence that the COVID-19 vaccines harm a person’s ability to become pregnant or that the vaccines have any negative effects on the fetus. Still, the CDC is always collecting data using a program called V-safe, to make sure that no issues arise.

COVID-19 vaccines and infertility

There is currently no data linking the vaccine to infertility. There have been thousands of people who became pregnant after receiving the COVID vaccines and there’s no evidence that it affects a person’s chances of conceiving (CDC, 2021).


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