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Expect Mild Side Effects From COVID-19 Vaccines, CDC Advisory Group Says

physicians placing bandage on patient's arm after vaccine
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Key Takeaways

  • Participants in COVID-19 vaccine clinical trials have experienced some side effects, but they have been largely mild.
  • Side effects are expected with many vaccines. It’s an indication that your immune system is revving up. 
  • Not having side effects does not mean the vaccine is ineffective.

Members of the Advisory Committee on Immunization Practice (ACIP), a group which advises the Centers for Disease Control and Prevention (CDC), meet regularly to talk about the vaccines in development to prevent COVID-19. At a November 23 meeting, several members recommended that health providers be honest with Americans about the coming COVID-19 vaccines. The message they want to send: Yes, there will be side effects, but the data released so far shows they’re largely mild. 

Health experts, including the ACIP members, are worried that concerns about side effects could result in many people not getting the vaccine. According to minutes from the meeting, the committee members feel that “early experience with [the] vaccine will be very important to increase interest and demand. Transparency is essential to improve trust and acceptability.”  

That transparency includes letting people know they should expect some possible side effects. Those side effects may include:

  • Pain and redness at the injection site
  • Headache
  • Stiffness
  • Body aches

“Those are all signs that the vaccines are producing an immunologic response, just as we want them to,” said Kathleen M. Neuzil, MD, MPH, FIDSA, director of the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine, at a reporter’s briefing hosted by the Infectious Diseases Society of America on Thursday.

The first COVID-19 vaccines that are expected to be approved require two doses about a month apart. Another ACIP concern is that unexpected side effects after the first shot could keep people from coming back for a second dose. Neuzil says both doses will be necessary for immunity.

Side Effects Shown In Clinical Trials

The companies first in line to present their vaccine data to the Food and Drug Administration (FDA), Pfizer and Moderna, have released information on the side effects experienced during clinical trials to test the safety and effectiveness of the vaccines. 

Pfizer Side Effects

Pfizer, whose vaccine will be reviewed by the FDA on December 10, reported no serious side effects among the 43,000 clinical trial participants. The most common side effect was fatigue, experienced by 3.8% of participants, followed by headache, experienced by 2%.

Moderna Side Effects

Moderna, who will present its clinical trial data to the FDA on December 17, reported that the majority of side effects among the 30,000 participants were mild or moderate. After the first dose, 2.7% of participants reported pain at the injection site.

More participants experienced side effects after the second dose, although they didn't last long:

  • 9.7% experienced fatigue
  • 8.9% experienced muscle ache
  • 5.2% experienced joint stiffness
  • 4.5% experienced headache
  • 4.1% experienced pain
  • 2% experienced erythema/redness at the injection site

What This Means For You

When it's time for you to get your vaccine to protect against COVID-19, expect your doctor to discuss possible mild side effects.

At a December 3 briefing from the Infectious Disease Society of America (IDSA), C. Buddy Creech, MD, MPH, FPIDS, director of the Vanderbilt Vaccine Research Program said the side effects seen so far in the coronavirus clinical trials are similar to those seen in other vaccines already in use for other diseases.

“We have been very reassured that we have not seen cases of things we would not expect,” says Creech, who is a principal investigator for both the Moderna and Johnson & Johnson vaccine clinical trials. Not everyone will experience side effects, he adds.

“It’s really important that people understand what they should be expecting,” Leana Wen, MD, MPH, an emergency physician and public health professor at George Washington University, tells Verywell. “Side effects from a vaccine are very normal. It’s the body’s response to revving up the immune system. People will have different reactions, or none at all, as is the case with all vaccines”

Wen says that when she and her fellow doctors advise patients on the COVID-19 vaccines, “we should not be minimizing the side effects; we should be explaining them.” 

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  1. U.S. Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Announces Advisory Committee Meeting to Discuss COVID-19 Vaccine Candidate. November 20, 2020.

  2. Pfizer. PFIZER AND BIONTECH CONCLUDE PHASE 3 STUDY OF COVID-19 VACCINE CANDIDATE, MEETING ALL PRIMARY EFFICACY ENDPOINTS. November 18, 2020.

  3. U.S. Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Announces Advisory Committee Meeting to Discuss Second COVID-19 Vaccine Candidate. November 30, 2020.

  4. Moderna. Moderna’s COVID-19 Vaccine Candidate Meets its Primary Efficacy Endpoint in the First Interim Analysis of the Phase 3 COVE Study. November 16, 2020.