Study finds same arm COVID-19 shots may trigger better immune response

If you're planning to get a flu shot and one of the new COVID-19 shots rolling out this week, you may want to consider getting your injections in the same arm.

German researchers found people who received a COVID-19 vaccine and then a booster in the same arm produced higher levels of protective "killer T-cells" than those who got the same vaccinations in different arms.

The Saarland University team measured the volunteers' antibody levels two weeks after they received their second shot.

They found the "killer T cells" in 67% of those who got both shots in the same arm, compared to 43% in those who received their injections in different arms.

The study was published in the medical journal EBioMedicine.

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Dr. Felipe Lobelo, physician director for epidemiology for Kaiser Permanente Georgia, says the findings are intriguing.

"It makes sense that you get two shots in the same arm those are going to stimulate the activity of the immune cells that are located in the lymph nodes in that area."

Restimulating the immune cells in those same lymph nodes with another shot may trigger a stronger immune response, at least in theory, Lobelo says.

Still, he cautions, this was a small study, looking at data for 303 volunteers, and the results would have to be replicated on a much larger scale in order for the medical community to recommend same-arm vaccinations.

"But I see no downside of trying to get, you know, the shots, if you remember which arm you got it last time, to get it in the same in the same arm," Dr. Lobelo says. "The concept could apply to COVID, to flu, to RSV, and the typical vaccines that we get year to year."

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The CDC is recommending both the flu vaccine and the updated COVID-19 shots for Americans 6 months and older.

And the agency says it is safe to get a flu and COVID-19 shot at the same time.

The most common side effects tend to be soreness, redness, and/or swelling in the arm where the injection is given.

So, Dr. Lobelo says whether you go for both shots in the same arm, or shots in different arms, is really a matter of personal preference.

"If you want to do it, there is no problem," he says. "But it's also not, you know, a huge problem if you don't."