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

Members of the Advisory Committee on Immunization Practice (ACIP), a group that advises the Centers for Disease Control and Prevention (CDC), have been meeting regularly to talk about COVID-19 vaccines.

Healthcare providers have been encouraged by the group to be honest with their patients about the vaccines—specifically, about possible side effects.

Many people are unsure what to expect when they get a COVID-19 vaccine. Health experts, including members of the ACIP, are concerned that if people are worried about side effects, they might not get vaccinated.

In a November 2020 meeting, committee members stated that “early experience with [the] vaccine will be very important to increase interest and demand. Transparency is essential to improve trust and acceptability.”

The Centers for Disease Control and Prevention (CDC) advises that people might feel a little unwell for a few days after they get the vaccine. They might feel a little like they have the flu, with a mild fever and fatigue.

Some people have experienced side effects after the second dose of the vaccine but not the first. If you do have mild side effects after getting your first dose, do not let that stop you from getting your second dose. You need to get both doses within the recommended timeframe to be protected.

During a reporter's briefing that was hosted by the Infectious Diseases Society of America, Kathleen M. Neuzil, MD, MPH, FIDSA, director of the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine, explained that these side effects "are all signs that the vaccines are producing an immunologic response, just as we want them to."

Side Effects in Clinical Trials

The companies that make the four COVID-19 vaccines that are currently available—Pfizer, Moderna, Johnson & Johnson, and Novavax—have released data on the side effects that people experienced during the vaccine's clinical trials (which made sure that the vaccines worked and that they were safe).

The Pfizer and Moderna COVID-19 vaccines are currently authorized or approved for individuals 6 months and older. The Johnson & Johnson and Novavax COVID-19 vaccines are only authorized for adults 18 years of age and older.

Pfizer Vaccine Side Effects

Overall, most of the more than 43,000 participants in Pfizer's vaccine trial tolerated the vaccine well. The most commonly reported side effects that were rated as severe (Grade 3) were fatigue (3.8% after the first or second dose) and headache (2% after the second dose).

Other side effects that people in the trial might have reported as severe occurred less than 2% of the time and were therefore not considered significant.

In another clinical trial that followed 3,100 individuals ages 5 to 11 who received the vaccine, the most commonly reported side effects were injection site pain, redness and swelling, fatigue, headache, muscle and/or joint pain, chills, fever, swollen lymph nodes, nausea, and decreased appetite. Overall, they were considered mild to moderate and usually went away within a day or two.

The Food and Drug Administration (FDA) notes that side effects may last several days and appear to be more common after getting the second dose of the vaccine. Common side effects can include pain at the site of the injection, tiredness, headache, muscle pain, chills, joint pain, and fever.

Moderna Vaccine Side Effects

Most of the side effects reported by the more than 30,000 participants in Moderna's vaccine clinical trial were mild and did not last long. Like Pfizer, Moderna noted which side effects were rated as severe and reported with a frequency of 2% or more. There were some differences in reports of side effects between the first and second doses.

The most commonly reported side effect that was rated as severe after the first dose was pain at the injection site (2.7%). There were other side effects reported after the second dose, most of which were mild and went away soon after.

The most commonly reported side effects after the second dose of vaccine that were rated as severe were:

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

As with Pfizer's vaccine, the FDA notes that people can experience side effects after receiving either dose, but that they were more frequently reported after the second dose.

Johnson & Johnson Vaccine Side Effects

Initial safety information released for the vaccine shows that the most common reactions after the vaccine was administered included:

• Injection site pain, redness, or swelling
• Fatigue
• Headache
• Muscle aches
• Nausea
• Fever
  

Novavax Vaccine Side Effects

Adults who took part in Novavax's Phase 3 trials were asked to record any local or systemic reactions after each dose of the vaccine.

The most commonly reported side effects were:

• Injection site pain, swelling, and redness
• Fatigue
• Muscle pain
• Headache
• Joint pain
• Nausea/vomiting
• Fever
• Chills
  

Rare and Serious Side Effects

While it is uncommon, some people have had more serious or unusual side effects after getting the COVID-19 vaccine. Some of these side effects, such as fainting (syncope) are related to getting the shot (a vasovagal response). These side effects can be distressing but are usually not serious. However, they need to be prevented because people can get injured when they faint.

Other reactions are caused by an allergy and can be serious. According to data from the CDC, a small number of people have experienced anaphylactic reactions after getting the COVID-19 vaccine. Severe reactions typically happen soon after a person gets a vaccine, often within minutes.

All providers who are administering COVID-19 vaccines have to know what to do if someone getting a shot has a serious reaction. This could include knowing how to administer an EpiPen or seeking emergency care.

The CDC advises that people who have a history of serious allergies, including anaphylactic reactions, should talk to their provider before getting the COVID-19 vaccine.

Updates were made to both the Pfizer and Moderna COVID-19 vaccine fact sheets for healthcare providers and vaccine recipients and caregivers about the rare risk of developing myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining outside the heart).

Warnings were also added to the Johnson & Johnson fact sheets for healthcare providers and vaccine recipients and caregivers about the rare risks of thrombosis with thrombocytopenia and Guillain-Barré syndrome.

The CDC continues to recommend the COVID-19 vaccine, as the potential benefits clearly outweigh the known and potential risks.

Talk to Your Provider

C. Buddy Creech, MD, MPH, FPIDS, director of the Vanderbilt Vaccine Research Program, explained during a press briefing that the side effects seen so far in the COVID-19 vaccine clinical trials are similar to side effects that are common with other vaccines.

“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. Creech adds that not everyone who gets the vaccine will experience side effects.

“It’s really important that people understand what they should be expecting,” Leana Wen, MD, MSc, an emergency physician and and visiting professor of health policy and management 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.” 

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.