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Here’s why your second coronavirus vaccine dose might have more of a kick to it

Updated Feb 8th, 2021 11:56AM EST
Coronavirus vaccine
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  • A growing number of reports have shared how people are feeling side effects more intensely following the second dose of their coronavirus vaccine.
  • Many COVID-19 vaccine recipients say those side effects include things like fever, headaches, and pain at the injection site.
  • Here’s why the side effects can be more intense with the second dose of the coronavirus vaccine, and why you shouldn’t worry.

By now, you might have seen a growing number of reports about how the side effects that people are experiencing with their second coronavirus vaccine jab have felt more intense than those from the first shot. Indeed, both Moderna and Pfizer acknowledged in their documentation they each submitted to the FDA that there was a marked difference in the side effects that volunteers experienced when receiving both doses of each drugmaker’s two-shot vaccine. Take Moderna’s statement about this: “Grace 3 solicited local adverse reactions were more frequently reported after Dose 2 than Dose 1.”

Those Grade 3 reactions can include things like swelling, pain, body aches, and fever. Bloomberg’s vaccine tracker shows that, as of the time of this writing, 36.7 million coronavirus vaccine doses have been administered in the US — so at least millions of people are proceeding ahead, not letting concern about possible side effects deter them from getting vaccinated. Still, the reports about stronger side effects associated with the second COVID shot might give some people pause, so what do you need to know about why that’s the case? Should you be worried? Read on for the details.

There’s an analogy that, imperfect as it is, might help explain why the side effects are so heightened with the second coronavirus vaccine dose. University of Arizona evolutionary biology professor Michael Worobey put it like this in an interview with CNN: Imagine you’ve just looked out your window and caught a peeping Tom. You’d be immediately creeped out, you might file a police report and take all the obvious initial first steps and precautions.

Now, imagine how freaked out you’d be — and how much more intense your emotional response might be — if a week later, a month later, you see that same creeper a second time.

“With the first dose” of a vaccine, Worobey explained, “you are having to generate an immune response from the ground up.” That first jab is akin to something like a wanted poster, alerting people to be on the lookout for that creeper from our analogy. The second dose of the vaccine, in which the body is given another prompt, is akin to seeing someone you remember from the wanted poster — and everything kicks into high gear in response.

Other vaccines will be coming online that are comprised of only a one-shot regimen, but for the two-dose shots from companies like Pfizer, people have reported side effects like fever, fatigue, headaches, and pain at the injection site following the second dose. “You end up with a finely-tuned B-cell population,” Worobey said, by way of explaining what’s going on here. “Then, the second time you give a person the shot, those cells are sitting around like a clone army and can immediately start producing a very big immune response, which is what is happening when people feel like they have been kicked in the teeth.”

Andy Meek Trending News Editor

Andy Meek is a reporter based in Memphis who has covered media, entertainment, and culture for over 20 years. His work has appeared in outlets including The Guardian, Forbes, and The Financial Times, and he’s written for BGR since 2015. Andy's coverage includes technology and entertainment, and he has a particular interest in all things streaming.

Over the years, he’s interviewed legendary figures in entertainment and tech that range from Stan Lee to John McAfee, Peter Thiel, and Reed Hastings.

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