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SALT LAKE CITY — The next time someone giving you a shot asks, "Which arm?" don't be cavalier. New research suggests the question may be more important than you think — at least if the vaccine calls for two doses.
Researchers at Oregon Health & Science University looked at the antibodies in 947 people who got two-dose COVID-19 vaccinations early in the pandemic. Some of them were employees who agreed to be randomized to get the second dose in the same or the opposite arm than the one poked for the first dose.
The findings are published in The Journal of Clinical Investigation.
The effect isn't small: Participants got as much as a fourfold increase in immune response when they alternated arms for a multi-dose vaccine, the researchers said.
A news release from the university said that the researchers tested serum samples at different times after vaccination. "They found a substantial increase in the magnitude and breadth of the antibody response among people who had 'contralateral' — or a shot in each arm — boosting compared with those who did not."
They said the response showed clearly three weeks after the second booster and lasted longer than 13 months. "Investigators found heightened immunity to the original SARS-CoV-2 strain and an even stronger immune response to the omicron variant that emerged roughly a year after arm alternation," they reported.
They theorize that a shot in different arms activates different lymph nodes in each arm. And they speculate that what they found with COVID-19 vaccines probably holds true for other vaccines, as well.
