COVID Vaccine Side Effects: Everything You Need to Know

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In the United States, we now have three vaccines — Pfizer, Moderna, and Johnson & Johnson — available to combat COVID-19. As the rollout of life-saving shots ramps up across the country, concerns about their potential side effects are one of the main reasons keeping eligible adults from rolling up their sleeves and getting a jab, according to a new report by Carnegie Mellon University. In partnership Facebook, researchers found vaccine hesitancy is highest in those who fear side effects, threatening our nation’s efforts in the race towards herd immunity. Below is everything you need to know about the extent and nature of the vaccines’ side effects, and how to deal with them.

Possible Vaccine Side Effects

There is no question that the currently available vaccines are effective and safe. While many people who receive a COVID-19 vaccine have no side effects, there’s a chance you could have a reaction to the shot.

The reported side effects are similar for all federally approved vaccines: injection-site reactions (including pain, redness, swelling, or tenderness), fatigue, headaches, and chills. A smaller number of people experienced joint pain and fever. According to the CDC, the side effects “may feel like flu and may even affect your ability to do daily activities, but they should go away in a few days.”

Of the first 13 million people who received either the Pfizer or Moderna shot in the U.S., the CDC received 6,994 reports of adverse reactions following vaccination; 91 percent were classified as nonserious and 9 percent as serious. The most commonly reported side effects were headaches (22 percent of those reporting symptoms), fatigue (17 percent), and dizziness (17 percent). Severe reactions like anaphylaxis are rare — only 4.5 cases per million doses administered.

If you do experience a mild to moderate reaction, don’t freak out — side effects are normal signs that your body is building protection against the virus, should you ever come into contact with it. Plus, the risk of temporary discomfort from a COVID-19 jab is far outweighed by the protection it offers against the deadly disease.

Are Reactions More Likely With Certain Vaccines?

Researchers have seen more allergic reactions to the Moderna shot than the Pfizer vaccine: In a new study out this week, 2.2 percent of subjects inoculated with the Moderna shot reported symptoms, compared to 1.95 percent of those who took Pfizer’s.

So far, there have been fewer cases of allergic reactions to the newest vaccine on the market — the Johnson & Johnson COVID-19 vaccine — compared to the two mRNA vaccines approved in December.

“It’s better tolerated than the Pfizer or Moderna vaccine in terms of local, what we call reactogenicity — [it] causes less people to have a sore arm, less people have what we call systemic side effects, including fatigue, fever, myalgias, [and] headache,” Dr. Paul Goepfert, a professor of medicine at the University of Alabama at Birmingham and the director of the Alabama Vaccine Research Clinic, told NBC News.

The Second Dose Can Pack a Punch

Some people report experiencing more side effects after their second dose. “The second dose is really like a booster dose,” Dr. Bill Moss, a pediatrician and professor of infectious disease epidemiology at Johns Hopkins Bloomberg School of Public Health, told Today. The body may react more violently to the second dose of Pfizer’s or Moderna’s shot because you’re already primed with that first dose and beginning to make antibodies against the virus.

Younger People Are More Likely to Experience Side Effects

If you’ve heard that younger people are reporting more side effects than people over 55, you’ve heard right. In the Pfizer vaccine trial, for instance, participants between the ages of 18 and 55 reported fever after the second dose at a higher rate than those over 55; the younger group reported more localized pain as well. Researchers are still studying why this is the case, but they say it’s likely related to the declining immune response that comes with age.

Women Are More Likely to Experience Side Effects

Women are also reporting more severe side effects after receiving COVID-19 vaccines, according to the New York Times. In the first month of coronavirus vaccination in the U.S., women received about 61 percent of the doses but accounted for 79 percent of reported side effects, according to a CDC report. “This sex difference is completely consistent with past reports of other vaccines,” Sabra Klein, an immunologist at the Johns Hopkins Bloomberg School of Public Health, told the New York Times, adding that sex hormones and genetics are a major explanation for why vaccine side effects hit women harder. “Women have greater immunity, whether it’s to ourselves, whether it’s to a vaccine antigen, whether it’s to a virus.”

What Should People Do If They Have Side Effects?

If you have hives or any respiratory distress within four hours of getting a vaccine, seek immediate medical attention, as you could be having an allergic reaction. The CDC also says that you should call your doctor if redness or tenderness at the injection site increases after 24 hours, or “if your side effects are worrying you or do not seem to be going away after a few days.”

For most people, though, side effects are not likely to require outside attention and can be managed with rest or an over-the-counter pain reliever such as acetaminophen or ibuprofen. Taking pain medications ahead of your shot is not recommended by the CDC, since it’s not clear how that could interfere with the vaccine’s effectiveness.

If You Don’t Have a Reaction, Is the Vaccine Still Working?

While side effects are an indication that the vaccine is doing its job, not everyone who gets vaccinated will experience them. In the Pfizer and Moderna trials, for instance, a significant percentage of participants did not have any of the common side effects. The lack of side effects does not indicate that the vaccine is not working; just “consider yourself lucky,” Harvard Medical School physician Abraar Karan told NPR.

Side effects or not, it’s important to note that anyone fully vaccinated still needs to follow COVID-safe protocols outlined by the CDC.

This piece has been updated.

COVID Vaccine Side Effects: Everything You Need to Know