COVID-19 vaccine side effects: What to know

California Gov. Gavin Newsom applauds as nurse Helen Cordova receives a COVID-19 vaccine at Kaiser Permanente in Los Angeles.

By Matthew BallingerUtility Journalism Editor

Dec. 16, 2020 12:54 PM PT

For most people, the only side effects of the Pfizer-BioNTech vaccine against COVID-19, rolling out now in California and across the U.S., might be some arm pain where you get the shot, of course, and some flu-like symptoms. Most people in the clinical trial reported that their side effects went away after about two days.

Some reports have surfaced regarding allergic reactions, so people with severe allergies should discuss their health history and any risks with their doctor before getting the shot.

Here’s what Pfizer lists as side effects reported in its clinical trial, along with the percentage of people age 18 to 55 who reported them after the first dose:

Redness at injection site (4.5%)
Swelling at injection site (5.8%)
Pain at injection site (83.1%)
Fever (3.7%)
Fatigue (47.4%)
Headache (41.9%)
Chills (14%)
Vomiting (1.2%)
Diarrhea (11.1%)
New or worsened muscle pain (21.3%)
New or worsened joint pain (11%)

People older than 55 reported side effects at slightly lower rates. You can read detailed reports about side effects in section 6.1 here.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, discusses side effects of the vaccine at about the 16-minute mark in a video conversation with the editor of the Journal of the American Medical Assn.

As for allergic reactions, the U.S. Centers for Disease Control and Prevention recommends that people who have had severe allergic reactions, such as anaphylaxis, to other vaccines or injectable medications should be monitored for 30 minutes if they receive the shot. (Anaphylaxis is a life-threatening allergic reaction that can occur within minutes of exposure to an allergen.)

The CDC recommends that people who have other allergies, such as to food or pets, should be vaccinated. You’ll talk to your doctor first and be monitored for 15 minutes after your injection.

Five things you need to know about COVID-19

UPDATED Oct. 2, 2020 | 5:15 PM

What are the symptoms of COVID-19?

A lot of them are the same as symptoms of a cold or the flu: cough, sore throat, congestion or a runny nose, fatigue, muscle or body aches, fever or chills, and shortness of breath. A person with COVID-19 may also experience diarrhea, nausea or vomiting, or a new loss of taste or smell. In cases of serious illness, it can take time for symptoms to worsen.

How long does it take for symptoms to appear after a person is exposed to the coronavirus?

The first symptoms can appear in as few as two days, but it can also take as long as two weeks, according to the CDC. An incubation period of four or five days is more typical. However, a significant proportion of people who are infected — perhaps as much as 45% — never develop any symptoms, researchers say.

What should I do if I think I'm infected?

If you have symptoms of COVID-19 or you’ve been in close contact with someone who has it, the CDC recommends that you get a coronavirus test. Until you get your test results, you should assume you are infected. That means staying at home as much as possible so that you don’t risk infecting others. Of course, if you’re having a medical emergency, don’t be afraid to call 911.

Some diagnostic tests look for genetic evidence of the virus in a sample of saliva or a specimen collected from the nose or throat. Others can detect specific coronavirus molecules that prompt the immune system to produce infection-fighting antibodies.

How can I reduce my risk of infection?

Limit contact with people outside of your household. When you do go out, wear a mask that covers your nose and mouth and stay at least six feet away from others whenever possible. Clean your hands frequently by using soap and water for 20 seconds or a sanitizer that contains at least 60% alcohol. Avoid touching your eyes, nose or mouth if your hands are dirty. At home, clean and disinfect tables, doorknobs, faucets and other frequently touched surfaces once a day.

How did the pandemic start?

Scientists think it began with a close relative of the novel coronavirus that has been circulating in bats and other animals for so long that it no longer makes them sick. That virus must have gained a key mutation that allowed it to infect humans. Health officials in China reported the first cases of the respiratory illness that came to be known as COVID-19 in December 2019. The first known case in Los Angeles was in January. California has had more than 800,000 confirmed cases since.

People who have had severe allergic reactions to any components of the Pfizer vaccine should not receive the shot.

Here’s the list of the exact components in the vaccine from the prescribing documentation:

“The Pfizer-BioNTech COVID-19 Vaccine is supplied as a frozen suspension in multiple dose vials; each vial must be diluted with 1.8 mL of sterile 0.9% Sodium Chloride Injection, USP prior to use to form the vaccine.

“Each dose of the Pfizer-BioNTech COVID-19 Vaccine contains 30 mcg of a nucleoside-modified messenger RNA (modRNA) encoding the viral spike (S) glycoprotein of SARS-CoV-2.

“Each dose of the Pfizer-BioNTech COVID-19 Vaccine also includes the following ingredients: lipids (0.43 mg (4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), 0.05 mg 2[(polyethylene glycol)-2000]-N,N-ditetradecylacetamide, 0.09 mg 1,2-distearoyl-sn-glycero-3-phosphocholine, and 0.2 mg cholesterol), 0.01 mg potassium chloride, 0.01 mg monobasic potassium phosphate, 0.36 mg sodium chloride, 0.07 mg dibasic sodium phosphate dihydrate, and 6 mg sucrose. The diluent (0.9% Sodium Chloride Injection, USP) contributes an additional 2.16 mg sodium chloride per dose.

“The Pfizer-BioNTech COVID-19 Vaccine does not contain preservative. The vial stoppers are not made with natural rubber latex.”

The COVID-19 vaccine from Pfizer and BioNTech that has been approved for emergency use was subject to well-established procedures to evaluate vaccine safety by scientists at the U.S. Food and Drug Administration and elsewhere. California and other Western states have also endorsed the Pfizer vaccine’s safety. Early on in Britain’s first vaccinations, two people may have had allergic reactions, but they recovered.

For more questions and answers about COVID-19 vaccines, see our FAQ.