- All three coronavirus vaccines authorized in the U.S. can cause mild to moderate side effects.
- The Johnson & Johnson injection usually has fewer side effects than the Pfizer or Moderna injection.
- The elderly observed fewer side effects than younger adults in all three clinical trials.
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If you are vaccinated, your arm may be sore.
Injection site pain is the most common side effect of all three coronavirus vaccines authorized in the United States.
In general, vaccines produce mild to moderate side effects that should not last more than a few days. Side effects usually appear 12 to 24 hours after the injection. They are often a sign that the body is creating immunity to the virus.
“It is important to remember: when people have side effects from vaccines, it’s not really because of the vaccine; it’s more about the body’s immune response to the vaccine, ”Dr. Vivek Cherian, a Baltimore intern, told Insider.
Scroll through the table below to see which side effects are common based on your age group, which vaccine from the manufacturer you are taking and whether you are taking one or two doses. In general, older people have fewer side effects than younger adults, as our immune response gradually weakens with age. For two-dose vaccines, such as Pfizer and Moderna, the second dose amplifies an existing immune response, so that people usually feel more exhausted after that dose.
Vaccines stimulate our bodies to produce antibodies against the coronavirus. But because our immune system cannot distinguish between a real infection and a vaccine-induced response, they still release inflammatory chemicals to protect us. That is why people can develop fever, muscle aches, fatigue or headaches right after vaccinations.
Johnson & Johnson injection has fewer side effects
In general, the Johnson & Johnson shot has milder and lesser side effects than the other two. Some experts suspect it is because it is a single shot.
Almost 62% of participants under the age of 59 in the Johnson & Johnson study developed side effects, compared with 45% of people aged 60 and over.
This is relatively similar to the side effects reported after a dose of Moderna vaccine: about 57% of people under 65 in this trial developed side effects, compared with 48% of people over 65. After the second dose of Moderna, however, almost 82% of people in the younger group developed side effects, compared with almost 72% of older adults.
But Johnson & Johnson’s injection also appears to be less effective overall: clinical trials suggest that the vaccine is 66% effective in preventing COVID-19. Pfizer and Moderna vaccines are each more than 90% effective. However, it is difficult to compare companies’ tests side by side, as they occurred at different stages of the pandemic and in different geographic regions.
Coronavirus vaccines are injected into the muscle.
Getty / David Greedy
Common side effects include fatigue and headache
As soon as the vaccine reaches your arm, blood flow increases and immune cells enter the picture. This can result in pain, redness, or swelling at the injection site.
The reaction is more common after Pfizer and Moderna vaccines than after Johnson & Johnson vaccines. Across all age groups, less than 50% of participants in the Johnson & Johnson clinical trial reported pain at the injection site, compared with 92% of participants in Moderna and 84% of participants from Pfizer.
Headache and fatigue were also relatively common in all trials. About 69% of Moderna participants reported headaches compared to 55% of Pfizer participants and 39% of Johnson & Johnson.
In both the Pfizer and Moderna trials, about 63% of participants reported fatigue. Only 38% of participants reported fatigue in the Johnson & Johnson study, but the prevalence of these side effects also varied with age.
Younger adults saw more side effects, with a few exceptions
A woman takes a selfie after receiving the vaccine.
CRISTINA QUICLER / Contributor / Getty Images
Only a few side effects appear to be more or as common among elderly participants as they are among younger ones.
After the second dose of the Pfizer vaccine, joint painting was equally common in both groups, with about 22% to 23% reporting the effect. However, after the second dose of Moderna’s vaccine, pain in the body or muscles was more common in adults aged 66 and over (47%) than in younger adults (6%).
Although older adults tend to have fewer side effects in general, experts say there is no reason to believe that vaccines do not work so well among them.
“For the COVID-19 vaccine, we didn’t see a reduction in effectiveness as we get older, so that’s a really good thing,” said Cherian.
Younger people should also not worry too much about experiencing strong side effects.
“Dealing with some side effects of diarrhea or some muscle pain is much, much better than some of the serious and potentially fatal side effects of COVID-19 infection,” said Cherian.