Right or left arm? It may actually matter where you get your COVID booster, study shows

Do you always get your COVID boosters in the same arm? New research suggests that may be more effective for sequential vaccinations rather than alternating. Saarland University immunology researcher Laura Ziegler and colleagues published peer-reviewed results from a study indicating "'that ipsilateral vaccinations generate a stronger immune response than contralateral vaccinations."

From EurekAlert:

In an ipsilateral vaccination the vaccine is injected twice into the same arm. In a contralateral vaccination, the primary vaccination is delivered to the left arm while the booster is injected into the right arm, or vice versa. Germany's COVID-19 vaccination campaign provided an ideal setting in which to study this question. Laura Ziegler and Martina Sester were able to create a reliable dataset of 303 individuals who received the mRNA vaccine from Biontech as their primary and booster shots at the start of Germany's COVID-19 vaccination campaign.

The most striking result was that two weeks after the booster shot the number of cytotoxic CD8+ T cells, often referred to as 'killer T cells', was significantly higher in those individuals who had been injected in the same arm. '[…]

As Laura Ziegler only analysed data from individuals who had received two shots of the Biontech SARS-CoV-2 vaccine, the 23-year-old researcher is suitably cautious about generalizing the conclusions of her study. Further work is required before we know whether the study has implications for other sequential vaccinations, such as flu vaccinations or vaccinations against tropical diseases.