New study shows alternating arm for vaccine doses may improve immunity

SALT LAKE CITY — With two-dose vaccinations, getting one shot in each arm may improve immunity up to four-fold, a new study shows.

Led by researchers at Oregon Health & Science University, the study tested 947 individuals, measuring the antibody response in their blood following two doses of the COVID-19 vaccine.

Previously, the site of vaccinations seemed inconsequential. The placement for injection was based on considerations like avoiding nearby nerves or other structures and ensuring the patient, particularly children, had enough muscle mass.

Of the 947 people tested, some received the second dose in the same arm while others got the second dose in the opposite arm as the first dose.

Researchers tested antibody samples at various times after vaccination and found a “substantial increase in the magnitude and breadth of the antibody response” among those who alternated arms for each dose or what’s known as “contralateral” boosting.

The improved immunity was evident just three weeks after the second dose and lasted beyond 13 months after it.

Those with contralateral boosting had heightened immunity to the original SARS-CoV-2 strain of COVID-19, and an even stronger immunity to the Omicron variant.

The study explained that researchers are not completely sure why this occurs, but that they speculate that by giving a shot in different arms, the vaccine activates different lymph nodes in each arm.

Although the study focused on the COVID-19 vaccine, researchers believe the immune response could be similar in other multi-dose vaccinations.