Covid Booster: These Are The Most Common Side Effects

A third dose of the coronavirus vaccine could cause symptoms on par with your previous jabs.

While the exact timeline still isn’t clear — and not all experts agree they are necessary right now — both Brits and Americans are soon likely to become eligible for a Covid-19 booster, possibly in a matter of days in the UK, according to health secretary Sajid Javid, and in the next few weeks in the US.

In fact, half a million British people with severely weakened immune systems are already being offered an additional Covid vaccination to keep infection at bay.

So, many people are wondering: what will the experience be like this time? Will I feel the same way I did when I rolled up my sleeves for my first and second jab?

Here’s what we know about the most common booster side effects so far.

Redness and swelling

Experts are still gathering information about the potential side effects of a third shot. The US Centers for Disease Control and Prevention is continually sorting through data to look for patterns and to detect new or unusual adverse events.

Data Pfizer submitted to US federal officials in its request for emergency use authorisation of a third dose, shows the main side effects have been very much in line with what we’ve seen with the first and second doses. The top side effect in its trial was pain at the injection site.

“There’s about 5% more pain at the injection site, but the vast majority of that is mild pain,” said Dean Blumberg, a paediatric infectious diseases specialist with UC Davis Health. He noted that the data available to experts so far is coming largely from pre-print data (not yet subject to peer review) or information presented at Advisory Committee on Immunization Practices meetings.

If you have a sore arm, the CDC suggests applying a cool, wet washcloth to the area. You should also continue to use and exercise or move your arm.

The side effects of a booster vaccine aren't expected to be too different than people's experience of their first and second jabs.
Teresa Colucci via Getty Images
The side effects of a booster vaccine aren't expected to be too different than people's experience of their first and second jabs.

Fatigue

Fatigue was the second-most-common side effect in Pfizer’s booster application; it was also a common side effect for earlier doses of coronavirus mRNA vaccinations

“It’s very similar to the second dose,” Blumberg said, who added, however, that there’s no way to know whether people who were really exhausted after the second shot would experience something similar after a third dose, or if they’d have a milder reaction — or vice versa.

The first dose of the mRNA vaccines (that’s Pfizer and Moderna) basically introduces your body to SARS-CoV-2; the second dose gets your immune system to recognizs the spike protein and mount an antibody response, which can lead to more intense symptoms as your body does what it’s supposed to do.

In a press release accompanying its bid for emergency use authorisation, Pfizer stated that the frequency of side effects was “similar to or better than” what people experienced after their second shots.

Muscle and joint pain

Muscle pain and joint pain are among the most common side effects experienced after the initial doses, and that’s likely to be the case again with booster shots.

But in general it’s not recommended to take over-the-counter medicines like ibuprofen, acetaminophen or aspirin before vaccination with the hopes of preventing side effects, because it may lessen the body’s immune response to the vaccine. (Still, experts have said that if you happen to take one of those medications beforehand, it’s probably fine, with one expert previously telling HuffPost the advice is “boringly conservative.” Just don’t go out of your way to do it if you don’t have to.)

Fever or chills

Fever and chills are another common side effect of the Covid-19 vaccines — and likely the booster dose as well.

Again, it’s reasonable to plan as though you might experience symptoms like you did after the Johnson & Johnson vaccine or the second dose of either of the two mRNA vaccines.

“Be prepared. If you get a third dose, you don’t want to have something really important planned the next day, like a birthday party, or a really important presentation at work, or a test if you’re a student,” Blumberg said. “I’d plan on being prepared for some reactions in the day or two following that third dose.”

Experts are still learning about Covid-19. The information in this story is what was known or available at the time of publication, but guidance could change as scientists discover more about the virus. To keep up to date with health advice and cases in your area, visit gov.uk/coronavirus and nhs.uk.