Which Arm Should You Get Your Vaccine In?

It may actually matter.

USA Today (“Left or right arm: Choosing where to get vaccinated matters, study suggests. Here’s why“):

When you roll up your sleeve to get routine vaccinations, do you prefer a jab in your right or left arm? New data suggests the choice you make matters.

Researchers in Germany found people who got all their shots in one arm had a stronger immune response than those who distributed shots between both arms, according to a study published last week in eBioMedicine, a peer-reviewed journal from The Lancet Discovery Science.

In the observational study, authors analyzed immune responses from about 300 people who never had COVID-19 and received two doses of Pfizer-BioNTech’s COVID-19 vaccine between March and September 2021.

Study participants were randomized to receive both doses in one arm or the second dose in the opposite arm. Two weeks after receiving the shots, researchers discovered certain immune cells – commonly known as “killer T cells” – were detected in 67% of people who received both injections in the same arm versus only 43% of those who got them in different arms.

People may respond better to sequential shots in the same arm because the vaccines are targeting the same lymph nodes, making them more active in producing immune cells to fight off infections, study authors suggest. While researchers detected a difference in these cells, they didn’t see a similar trend in spiked protein antibodies.

Although preliminary and small, the study shows how the reason why some people react differently to vaccines could go further than just age, sex and medical conditions, said Dr. Ofer Levy, a pediatric infectious disease specialist and director of the Precision Vaccines Program at Boston Children’s Hospital.

“This speaks to precision vaccination in the sense that everything matters,” said Levy, who is not affiliated with the study.

More research and data is needed but he says the study’s findings could have implications for vaccines outside of COVID-19 and help standardize how routine vaccinations are given.

“We need to be precise about how we discover, develop and deliver vaccines,” Levy said.

I’m always a wee bit skeptical of reporting on medical studies but this finding seems at least plausible.

I’ve always gotten shots in my left arm, since I’m right-handed and figure it makes sense to isolate soreness to my non-dominant side. I’m mildly surprised that people don’t always get their shots in the same arm.

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James Joyner
About James Joyner
James Joyner is Professor and Department Head of Security Studies at Marine Corps University's Command and Staff College. He's a former Army officer and Desert Storm veteran. Views expressed here are his own. Follow James on Twitter @DrJJoyner.


  1. Jen says:

    This is fascinating. Like Dr. Joyner, I always get my shots in my left (non-dominant) arm, mostly so I could do things like drive a stick-shift and write/work after the shot. I never would have guessed that it mattered to immunity.


  2. Kathy says:


    Same here.

    Except I sometimes get right and left mixed up, so the first Pfizer went into my right arm*. Second Pfizer and both AstraZeneca shots went into the left one.

    *For some reason, that was the only one that produced no pain in the injection site at all.

  3. Scott says:

    Actually, I don’t remember which arm I get my shots in. It is probably random depending on where I go. The last shots I got (23 Sep 2022) I got a Covid in one arm and the flu in the other.

    If I read the article right, it was tested just with COVID shots. Wonder if the same effect happens with a mixed bag of shots, like Shingrix or pneumonia -23.

  4. James Joyner says:

    @Scott: Good question. The last two COVID boosters I got were accompanied by a flu shot and the first round of Shingrix—and I got both in the left arm. The latter absolutely kicked my butt. It may well have been the cocktail, as the Shingrix second round had next to no effect on me.

  5. steve says:

    Could be true but this study is only suggestive I think. I am in the group the thinks we should use p values of 0.005 (some suggest 0.001) for significance if we are going to use p values*. This study is small and it just reaches significance. I wouldn’t hang my hat on a big change on how we vaccinate based on 300 people. OTOH, hard to see how it would hurt to have all in the same arm.


    *I suspect most people are aware that way too many studies are not reproducible. At a p of 0.05 there is about a 20% chance the study is not meaningful, not the 5% chance most people were taught or assumed.

  6. Beth says:

    As in most things, I go both ways.

  7. MarkedMan says:

    Speaking of which, isn’t there supposed to be a booster this fall? I haven’t heard anything about it lately.

  8. MarkedMan says:

    @Beth: Just “both”? 😉

  9. Daryl says:

    I literally laughed out loud…

  10. Daryl says:

    This is interesting because I got my first shot in my right arm, and then the second in my left.
    I found that the gain in magnetism was far greater after getting the shot in the left arm.
    I hadn’t really considered it until I read this.

  11. Beth says:
  12. Jen says:

    @James Joyner: I had the Shingrix shots independent of my covid and flu vaccinations, and that was my experience as well–Shingrix #1 absolutely kicked my butt, but the second I barely had a sore arm. My doc warned me that the shingles vaccine was a doozy.

  13. Jen says:

    @MarkedMan: NYT had a piece on the covid booster last week.

    Key excerpt:

    Pfizer, Moderna and Novavax are now working to update, test and mass-produce their vaccines, which will then need to be officially authorized by the F.D.A. Experts estimate that shots will be available to the public by late September or early October.

  14. Scott says:

    @Daryl: Still pissed that my brain can’t link into 5g even after 2 COVID shots and 2 boosters. Promises made. Promises not kept.

  15. a country lawyer says:

    Got my covid booster this morning in my left arm and the flu shot in the right.

  16. OzarkHillbilly says:

    I have to admit I’ve never paid much attention to the question. I think my usual response is to indicate which ever arm is closest to them.

    I am skeptical that there is any real world difference, but who knows. FTR, I’ve never had much, if any, physical reaction to a vaccine. Not even when I got multiple vaccines in one sit down.

  17. OzarkHillbilly says:

    @Jen: When I got my shingles vax, I also got the pnuemonia and flu shots. I suspect all 3 were in the same arm but can’t recollect. As I said above, no physical reaction to them.

  18. Jen says:

    @a country lawyer: Which booster? I thought the most recent one wasn’t available yet (see the excerpt above from the NYT).

    @OzarkHillbilly: Having lived abroad, my shot record is…thorough. The only vaccine I remember having issues with is the first Shingrix shot!

  19. Franklin says:

    @steve: This. Color me skeptical, partly because of the p value. But also just the general variability in people’s reactions to Covid. Furthermore, what’s the theory behind why doing it in the same arm would matter? If your immune system is *that* localized, even after months between shots, why would it confer immunity to where Covid generally invades your body (which is not a hole in your upper arm)?

  20. Argon says:

    Alas, the buttocks. Still overlooked as the easiest target for a needle.

  21. a country lawyer says:

    @Jen: This morning’s shot was my 3rd booster, 5 sticks altogether, counting the 2 initial shots of Pfizer.

  22. DrDaveT says:


    At a p of 0.05 there is about a 20% chance the study is not meaningful, not the 5% chance most people were taught or assumed.

    This is mostly due to p-hacking, which is almost required by current academic journal publication standards and tenure criteria, despite lip service to the contrary. I’m hoping I live long enough for the Bayesians to have finally buried the last frequentist who thought p-values were ever meaningful in any way.

  23. al Ameda says:

    I’m left-handed so I ask for the vaccine in the right arm.

    I typically do not have a negative reaction or extended soreness, but if I do I prefer it be in the right side not the left.

  24. Ken_L says:


    Alas, the buttocks. Still overlooked as the easiest target for a needle.

    But the left or the right?

  25. Kazzy says:

    @Ken_L: Whatever you do, don’t try to split the difference.

  26. Jax says:

    Hahahaha…..I just got back home to where I can read these comment threads comfortably on my computer and not on my iPad, and I gotta tell ya…..

    You guys are some funny fuckers. 😛 😛