One arm or two? How you get vaccinated may make a difference

One arm or two?  How you get vaccinated may make a difference

If you offer the same arm for each dose of a particular vaccine, you may need to reconsider. A new study suggests that alternating arms may lead to a stronger immune response.

Researchers studied responses to the first two doses of COVID-19 vaccines. Those who swapped arms showed a slight increase in immunity compared to those who got both doses in the same arm.

For individuals who respond poorly to vaccines due to age or health conditions, even a small boost could be significant, the researchers said. At this point in the pandemic, with most people getting multiple vaccine doses or becoming infected, alternative arms of Covid vaccines may not offer much benefit.

However, if these findings are confirmed by further studies, they could have implications for all multi-dose vaccines, including childhood immunizations.

Dr. Marcel E. said: “I’m not making recommendations at this point, because we need to understand this much better,” said Kirlin, an infectious disease physician at Oregon Health & Science University who led the work.

But “all things being equal, we should consider switching weapons.”

The few studies comparing the two approaches have been small and have produced mixed results. None of the studies showed a significant difference in immunity.

Jennifer Gommerman, head of the Department of Immunology at the University of Toronto, who was not involved in the new research, said that a study conducted on mice found that a single lymph node can generate strong immunity after vaccination.

“This means the lymph nodes are doing their job well,” she said, and most vaccines will do well targeting one arm.

For most people, extending the interval between doses — by three to four months, as happened in Canada for COVID vaccines, rather than the three to four weeks recommended in the U.S. — may provide greater benefit than switching arms, Gommerman said. .

Still, she added, it’s worth considering all of these strategies, because for immunocompromised people, “anything that helps their immune responses is worth doing.”

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

Participants, part of a larger research project, were randomly assigned to receive the second dose in the same arm as the first dose or in the opposite arm. The researchers excluded anyone who contracted coronavirus during the study.

Scientists found that switching arms increases antibody levels in the blood by up to four times. 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 about a year after the first Covid vaccines were licensed.

“It is a statistically significant fixed effect; Very large; “And it seems to be very durable,” Kerlin said.

The findings initially appear to contradict those of a German study last summer that showed that rolling up the same sleeve each time may lead to a better immune response. But that study measured antibody levels just two weeks after the second dose.

In that period, the new study also found similar results. But the pattern slowly shifted over subsequent months to higher levels of antibodies in those who switched arms.

The results of the new study were not a complete surprise to the German researchers.

“What they’re seeing is one of the options I was thinking about as a possibility, and it’s interesting that they’ve already noticed this kind of shift in effects,” said Martina Sester, an immunologist at Saarland University in Saarbrücken, Germany.

Switching arms with each dose could be “part of several measures that you can easily adopt that might lead to a successful immune response,” Sister said.

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