April 21, 2021


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How soon — and how long — could you feel side effects of COVID vaccines? What to know

Editor’s note: This story is available in Spanish here.

Scientists and doctors have been telling the public since before COVID-19 vaccines became available in the U.S. that side effects after the shot are normal and should be expected; it’s a sign your body is building a defense against the disease.

And don’t worry if you miss out on the joy that is cold sweats and achy bones, experts say. Some people may not experience side effects at all, even though their bodies are working just as hard.

That’s because no immune system is the same, which means side effects may last longer or be more intense in some people compared to others. So, just how long could arm pain, fever or fatigue last after COVID-19 vaccination? And how soon after getting the shot should you expect to feel side effects, if any at all?

The Centers for Disease Control and Prevention says side effects “may affect your ability to do daily activities, but they should go away in a few days.”

Here’s what late-stage clinical trials have found about side effects for each COVID-19 vaccine authorized for emergency use in the U.S.


Local reactions such as arm pain, swelling and redness after vaccination with the Pfizer COVID-19 shot first appeared any time between 0 (the day of vaccination) and two days after being jabbed among thousands of clinical trial participants. The effects generally lasted one to three days.

After their second dose, people 18 to 55 years old (78%) reported injection site pain more frequently than adults above age 55 (66%).

Systemic reactions such as fatigue, headache and muscle pain — the most common side effects after the Pfizer vaccine — appeared one to two days after either dose, and lasted for about one day.

Side effects were generally more frequent and intense after the second dose compared to the first, and felt more often and severely by younger adults.


The most common local reaction to the Moderna COVID-19 vaccine was arm pain, which occurred more often after the first shot and in younger adults. The majority of people said their arm pain began the day after vaccination and lasted for about two days after dose one and three days after dose two.

Swollen lymph nodes in the armpit of the vaccinated arm was the second most common local reaction to the Moderna shot and lasted about one day after the first dose and two days after the second dose.

Local side effects lasted more than a week in some people, occurring in 3.7% of vaccine recipients, and more often in younger adults.

Fatigue, headache and muscle pain after the Moderna shot began one to two days after vaccination, and generally lasted for about two days. Nearly 12% of people reported side effects that lasted for more than a week, including fatigue, headache, muscle pain and joint pain.

A total of seven people who received the vaccine during the trial said their fever lasted beyond a week, suggesting the long-lasting reaction is rare.

Johnson & Johnson

Injection site pain was the most common local side effect after receiving the one-dose Johnson & Johnson COVID-19 vaccine in late-stage clinical trials. It was felt most frequently in younger adults. Redness and swelling was also reported.

These reactions appeared within two days of vaccination. Skin redness and arm pain lasted for about two days, while swelling lasted for about three. About 2% of people reported pain that lasted for more than a week.

Headache and fatigue were the most common systemic side effects; they were felt within two days of vaccination and lasted for about the same time, except for nausea and fever, which lasted for about a day.

Some people experienced side effects for longer than a week: 1.6% of people with fatigue, 1.1% with muscle pain and 0.7% with headache.

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