Could switching arms for vaccinations increase immunity?

If you’ve presented the same arm for every dose of a particular vaccine, you may want to reconsider. Alternating arms may produce a more powerful immune response, a new study suggests.

The researchers studied responses to the first two doses of Covid-19 vaccines. Those who alternated arms showed a small increase in immunity over those who got both doses in the same arm.

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For individuals who respond poorly to vaccines because of age or health conditions, even a small boost may turn out to be significant, the researchers said. At this point in the pandemic, with most people having had multiple vaccine doses or infections, alternating arms for Covid vaccines may not offer much benefit. Yet, if confirmed by further study, the results could have implications for all multi-dose vaccines, including childhood immunisations.

“I’m not making recommendations at this point, because we need to understand this a lot better,” said Dr Marcel Curlin, an infectious disease physician at Oregon Health and Science University who led the work. But, “all things being equal, we ought to consider switching up the arms”.

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The few studies comparing the two approaches have been small and have produced mixed results. And none of the studies have shown a big difference in immunity.

In the new study, Dr Curlin and his colleagues repeatedly measured antibody levels in 54 pairs of university employees matched for age, gender and the time after vaccination.

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The participants, part of a larger research project, were randomised to get the second dose in the same arm as the first dose or in the opposite arm. The researchers excluded anyone who became infected with Covid during the study.

Switching the arms increased blood antibody levels by as much as fourfold, the scientists found. The results were published in The Journal of Clinical Investigation.

The immune response was stronger against both the original coronavirus and against the omicron variant, which emerged roughly a year after the authorisation of the first Covid vaccines. - This article originally appeared in the New York Times

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