If you’ve ever lined up for a jab—whether it’s the annual flu shot or a COVID-19 booster—you’ve probably been asked, ‘Which arm would you like it in?’
For most of us, it’s a split-second decision: dominant arm, non-dominant arm, or maybe just the one that’s less sore from gardening!
But new Australian research suggests that this seemingly trivial choice could actually make a difference to how well your body responds to the vaccine.
A recent clinical trial, published in the prestigious journal Cell, has shed light on the impact of vaccine placement.
The study, led by the Garvan Institute of Medical Research and the Kirby Institute at the University of New South Wales, involved 30 volunteers who received the Pfizer-BioNTech mRNA COVID-19 vaccine.
Here’s the twist: most participants received both their initial and booster shots in the same arm, while a smaller group switched arms for their second dose.
The results? Those who stuck with the same arm produced neutralising antibodies significantly faster than those who swapped sides.
It all comes down to how our immune system organises its defences. When you get a vaccine, immune cells in the lymph nodes near the injection site spring into action. These cells become ‘primed’ to recognise and fight off the virus if it shows up again.
If you get your booster in the same arm, you’re essentially giving those local immune cells a head start—they remember the first shot and can ramp up your body’s defences more quickly.
Professor Tri Phan, co-senior author of the study and director of Garvan’s precision immunology program, explains: ‘This is a fundamental discovery in how the immune system organises itself to respond better to external threats—nature has come up with this brilliant system and we’re just now beginning to understand it.’
Vaccines work by stimulating the development of immune cells that make antibodies, as well as ‘memory’ cells that remember the invader for next time.
The study found that when the booster is given in the same arm, these memory cells are better able to adapt and produce more effective antibodies—even as viruses mutate.
Interestingly, the research also highlighted the role of other immune cells called macrophages. These cells ‘talk’ to the memory B cells, helping them to fine-tune their response and create even better antibodies.
While there are currently no official guidelines about which arm to use for your vaccine, this research suggests there may be a real benefit to sticking with the same arm for your booster. It’s a simple step that could help your body mount a faster and more effective immune response.
Professor Phan says, ‘The findings show there is a benefit and offer a promising avenue for enhancing the effectiveness of vaccines.’
It turns out that the choice of arm for your vaccine isn’t just a matter of convenience—it could actually help your immune system respond more quickly and effectively.
While more research is needed, especially with larger groups and different types of vaccines, this is an exciting step forward in our understanding of how to get the most out of our jabs.
So next time you roll up your sleeve, you might want to give a little more thought to which arm you choose. It’s a small decision that could make a big difference!
What do you think about this new research? Have you ever considered which arm to use for a vaccine? Share your thoughts or experiences in the comments below.
Also read: The MMR vaccine doesn’t contain ‘aborted fetus debris’, as RFK Jr has claimed. Here’s the science
