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COVID-19 Vaccines: What About Side Effects?

Dec. 16, 2020 - Katie McCallum

This article was updated on December 19, 2020 to reflect the current state of the COVID-19 vaccine landscape.

The FDA has now granted Emergency Use Authorization (EUA) to two COVID-19 vaccines, the Pfizer and Moderna mRNA vaccines.

You probably have a few questions about these new vaccines, such as: What about side effects?

There are potential side effects to these new COVID-19 vaccines. But it's also important to know that, upon granting EUA, the FDA stated that the "known and potential benefits clearly outweigh its known and potential risks" of both the Pfizer and Moderna vaccines.

"What we certainly don't want is for people to avoid getting vaccinated because they're afraid of side effects," says Dr. H. Dirk Sostman, president of the Academic Institute at Houston Methodist. "In addition, since both the Pfizer and Moderna vaccines require two doses, we also don't want people to be surprised by the side effects and avoid getting their second dose as a result. You will need to get both doses to be protected."

While inconvenient, it may be reassuring to understand that these side effects are an indication that the vaccine is doing its job — helping your body develop immunity to the virus. This is tough work, so it's no surprise you "feel it."

What are the most common side effects of COVID-19 vaccines?

Before any new COVID-19 vaccine is made available to the public, the FDA and other experts will have reviewed a lot of information regarding both its safety and effectiveness. (Related: Here's What We Know About COVID-19 Vaccine Safety)

"Every COVID-19 vaccine will have undergone rigorous testing via clinical trials, as well as thorough external review by the FDA, CDC and their independent panels of experts," says Dr. Sostman. "Any potential side effects will be well-documented and made clear to the public."

The most common side effects of the Pfizer and Moderna COVID-19 vaccines are:

  • Pain, redness and swelling at the site of the shot
  • Fatigue
  • Headache
  • Muscle and joint pain
  • Low-grade fever and chills
  • Nausea/vomiting
  • Swollen lymph nodes

"One way to reduce the chance of uncomfortable side effects is to take a pain reliever, such as Tylenol, if you experience any discomfort," adds Dr. Sostman.

If you do become concerned about side effects you're experiencing, seek medical attention immediately or call 911 if the effects are severe. If they are not severe, call your doctor's office or use Houston Methodist Virtual Urgent Care.

"Ultimately, when compared to the very severe symptoms a person can develop while ill with COVID-19, vaccination remains one of the most effective ways to protect your health and keep your community safe during this pandemic," explains Dr. Sostman.

Can the COVID-19 vaccine get me sick?

While there are potential side effects to the vaccines, these reactions are a feature of receiving a vaccine — not of being infected with COVID-19.

"These vaccines cannot cause COVID-19," Dr. Sostman says. "Instead, what you may feel are the so-called 'reactogenic' effects of the vaccine working on your body and immune system."

There will ultimately be several different types of COVID-19 vaccines, and each vaccine will work in a slightly different way. The Pfizer and Moderna vaccines are mRNA vaccines. Not only are these much quicker to produce, one of the major advantages of this type of vaccine is that there's no chance that the vaccine can result in infection.

"These new mRNA vaccines rely on synthetic, noninfectious RNA material — which your cells then use to create a harmless viral component. Since this component cannot assemble into a complete virus, it can't actually make you sick. But, it can stimulate an immune response to the virus," explains Dr. Sostman. "The mRNA is then quickly degraded, so there's also no chance for it to affect your body beyond its role in helping to confer immunity."

What about adverse reactions to COVID-19 vaccination?

The bottom line is that no vaccine or drug is ever going to be completely free of side effects or adverse effects — COVID-19 vaccines included.

"It's true that we don't have years of long-term follow up for these vaccines yet. What we do have is months of follow-up that cover the period when adverse issues with vaccines are normally discovered," adds Dr. Sostman.

Lastly, as more and more people receive these vaccines, some very rare side effects may come to light — such as the adverse reactions seen to the Pfizer vaccine in two individuals in the United Kingdom.

"It appears that those two individuals had a medical history of serious allergic reactions and routinely carried EpiPens. Due to this new finding, the UK's medical regulatory agency has said people should not receive the vaccine if they have had a serious allergic reaction to a vaccine, medicine or food," warns Dr. Sostman. "Keep in mind, however, a severe allergic reaction isn't the same as seasonal allergies. A severe allergic reaction is one that causes life-threatening symptoms, such as chest pain and difficulty breathing, and this is a reaction that typically warrants a person to carry an EpiPen."

The CDC and the FDA will continue to monitor individuals who have received the vaccine to ensure that we completely understand any safety issues.

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