• The Moderna clinical trials found that injection site pain, fatigue, headache, and aches and pains were commonly reported after vaccination.
  • Since millions of people have gotten the vaccine outside of trials, the top side effects include pain at the injection site along with chills, headache, and fever.
  • In general, older adults are less likely to experience side effects after vaccination.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

Over 47 million doses of the Moderna vaccine have been administered to U.S. adults since the FDA issued emergency use authorization for the shot on December 18, 2020.

The Moderna clinical trials found that injection site pain, fatigue, headache, and aches and pains were commonly reported after vaccination.

Now, with so many shots going into arms, we’ve been able to get an even clearer look at the side effects the Moderna vaccine causes.

Like those involved in the clinical trials, people have commonly reported pain at the injection site along with chills, headache, and fever.

There have also been several reports of “COVID arm” after the Moderna vaccination, a harmless skin rash likely triggered by the vaccine ingredients.

The reactions are usually more intense after the second dose and in people who previously developed COVID-19.

Infectious disease doctors say these reactions are to be expected, as they indicate the immune system is doing its job in learning how to recognize and fight the coronavirus.

Pain at the injection site, chills, headache, and fever are the most common symptoms people experience after receiving the Moderna vaccine.

All of these reactions — which are temporary and nonthreatening — indicate the vaccine is doing its job. They typically clear up within a few days.

“As the vaccine works to ‘train’ your immune system to start developing antibodies, the pain is a sign of the inflammation that occurs as part of this process,” said Dr. Shobha Swaminathan, an associate professor of medicine at Rutgers New Jersey Medical School and clinical research site leader for the Rutgers Moderna trial.

Like other vaccines, every person’s response could be somewhat different.

In general, older adults are less likely to experience side effects after vaccination.

Recent data suggest women tend to experience more side effects after vaccination.

It’s unclear exactly why side effects could be different between sexes. Some health experts suspect women are more likely to report side effects, while others believe there’s a biological component.

Several people have also reported skin rashes on the arm where they received the shot — aka COVID arm.

“This is a pretty common side effect and probably has to do with the ingredients in the vaccine that are intended to teach the immune system that something dangerous is being introduced,” explained Dr. Anne Liu, infectious disease physician at Stanford Health Care.

Anaphylaxis, a severe allergic reaction, appears to be rare. Anaphylaxis also appears to be more common in women.

The Moderna shot is a messenger RNA (mRNA) vaccine that teaches our cells to make a piece of SARS-CoV-2 protein and mount an immune response against it.

That way, if a person were to be exposed to the coronavirus, their body would already know how to fight it and prevent severe disease.

The first dose is considered “the prime” and trains your body to recognize the virus, according to Swaminathan.

“Since that is the first exposure, reactions tend to be mild,” Swaminathan said.

The second dose, the “booster,” further cements the immune response.

“Since the patients have already ‘seen’ the vaccine from the first shot, the second booster is an exaggerated response to the same,” Swaminathan said.

Research also suggests reactions are more intense in people who previously had COVID-19 since they likely have some level of preexisting immunity.

Reactions to the Moderna vaccine are similar to those reported after the Pfizer vaccine, which is also an mRNA vaccine.

Recipients of both the Moderna and Pfizer mRNA vaccines commonly reported pain at the injection site and redness after the first dose, along with fatigue and joint pain after the second dose.

“The reactions to the mRNA vaccines have not been terribly different, certainly not to a degree that an individual should choose one or the other on the basis of side effects,” said Liu.

In clinical trials, the Johnson & Johnson shot was associated with milder side effects compared to the mRNA shots.

“Since Moderna and Pfizer require two shots and most side effects were from the second shot, the J&J vaccine may have slightly fewer side effects,” said Swaminathan.

With over 47 million doses of the Moderna vaccine administered to Americans, we’re getting a clearer picture of the types of side effects that can occur after vaccination.

Most commonly, people experience pain at the injection site and redness after the first dose, along with fatigue and joint pain after the second dose.

Reactions tend to be more intense after the second dose and in people who previously had COVID-19.

The reactions are to be expected and indicate the vaccine is doing its job in teaching the immune system how to recognize and fight the coronavirus.