Left arm or right arm? A choice that influences vaccine effectiveness 💉

A recent discovery could change how we administer vaccines. Researchers have observed that the choice of arm for injections influences the immune response.


The study, published in Cell, shows that macrophages in the lymph nodes near the injection site play a key role. These immune cells 'prepare' memory B cells for a faster and more effective response during a booster shot in the same arm.

Trials on mice were confirmed by a human clinical study with the Pfizer-BioNTech vaccine. Participants who received both doses in the same arm developed neutralizing antibodies more quickly. This difference is particularly notable against variants like Delta and Omicron.

Macrophages, often considered the 'garbage collectors' of the immune system, thus appear to have a more complex function. They orchestrate a more effective immune response when the booster is administered in the same location as the first dose.

This strategy could be crucial during a pandemic, where every week counts to achieve herd immunity. However, researchers note that the differences diminish over time, reassuring those who received their doses in different arms.

The implications of this discovery go beyond the current pandemic. It paves the way for designing vaccines that require fewer boosters by optimizing the interaction between memory B cells and macrophages.

The research team, led by Prof. Tri Phan and Prof. Anthony Kelleher, used cutting-edge imaging techniques to observe these mechanisms. Their work could influence future vaccination recommendations and research on next-generation vaccines.