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Why does my arm hurt more after the second COVID-19 vaccine dose?

Posted at 4:45 AM, Feb 11, 2021
and last updated 2021-02-11 08:49:14-05

The ABC15 Health Insider team is dedicated to getting you expert medical advice from the men and women who know it, see it every day in their work, and study it.

Part of our commitment to you is to answer your questions.

Judith Swanson wrote in and said, "I've had the first vaccine. How long is your arm sore for? After getting the first vaccine, what can I do other than wear a mask?"

We spoke to our Health Insider Dr. Piyush Gupta about this same topic this week and about reports from some that their arms have hurt more after receiving the second COVID-19 vaccination.

"In short, it's a good thing," explains Dr. Gupta. "Our body, when we get the first dose, we weren't as prepared, right? Our immune system is always on and is always prepared, but it was the first time this new, foreign invader is inside our body. Our body is still learning how to deal with it. Our body still hasn't developed the full immune response... Now, once we get the same sort of antigen or foreign body into our body, our body and our immune system are much more reactive. It's ready to go."

In short, your body's immune response may be greater the second time around, which could lead to more side effects, but Dr. Gupta says from what he has seen in the field, side effects for the second shot were similar to the first shot. But to explain the science behind it, he likened the experience to security guards protecting a building.

"There was one security guard outside the building. Now, there's 100! And as soon as that foreign invader comes up, the body knows how to defend it. And that's why we have these systemic side effects. The body starts to flood that area with more immune cells it starts to release these things called 'cytokines' and a lot of inflammation, and that's why we are feeling those symptoms - the fevers, the chills, the joint pain, and so forth -- because our body is in a pro-inflammatory state. Again, almost all of these symptoms are resolving within 24-48 hours. It's really a good thing."

As for the second part of Judith's question about what she can do other than wear a mask after getting the first vaccine, Dr. Gupta says just because you're fully vaccinated doesn't mean your behavior should change. You still need to wear a mask, practice social distancing, wash your hands, and stay home if you're feeling sick.

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