Ever wondered if it matters which arm you get your vaccine booster in? Turns out, it just might!

New research suggests that getting your booster shot in the same arm as your first jab could help your immune system gear up faster and stronger. This simple trick could speed up protection, especially during outbreaks of fast-changing viruses like COVID-19.

Why does the arm matter?
When you get a vaccine, immune cells take the viral or bacterial antigens to the closest lymph nodes - those little immune command centers near the injection site. There, memory B cells hang out, ready to spring into action if they see the pathogen again.

The research discovered that certain immune cells such as macrophages get “primed” after the first shot and help rally the memory B cells when a booster arrives - but only if it’s in the same place ⁽¹⁾.

In a human trial, 30 volunteers got the Pfizer COVID-19 vaccine booster—20 in the same arm, and 10 in the opposite arm ⁽²⁾. Guess what? Those who stuck to the same arm produced protective antibodies faster - within just one week after the booster!

Faster antibodies = faster protection
The antibodies from the “same-arm” group were not only quicker but also better at tackling variants like Delta and Omicron. While the difference faded by week four, that early immune boost could be a game changer during outbreaks.

What’s next?
If scientists can harness this local immune magic, future vaccines might need fewer boosters—saving time, doses, and hassle.

So next time you get a jab, remember: The same arm might just be your immune system’s favourite sidekick!

References

1. Dhenni R, Hoppé AC, Reynaldi A, Kyaw W, Handoko NT, Grootveld AK, et al. Macrophages direct location-dependent recall of B cell memory to vaccination. Cell [Internet]. 2025 Apr 29 [cited 2025 Jun 3]; Available from: https://www.sciencedirect.com/science/article/pii/S0092867425004076
2. Left arm, or right? The simple choice that might influence your response to vaccines [Internet]. [cited 2025 Jun 14]. Available from: https://www.gavi.org/vaccineswork/de-left-arm-or-right-simple-choice-might-influence-your-response-vaccines