Scientists in Germany looked at health data for 303 people who got the mRNA vaccine and then a booster shot. Their antibody levels were measured two weeks after the second shot. None of the people had had COVID before the vaccinations.
Scientists found that the number of protective “killer T cells” was higher in the 147 study participants who got both shots in the same arm, said the study published in EBioMedicine.
The killer cells were found in 67% of cases in which both shots went into the same arm, compared with 43% of cases with different arms.
“That may suggest that that ipsilateral vaccination (in the same arm) is more likely to provide better protection should the vaccinated person become infected with the SARS-CoV-2 virus,” Laura Ziegler, a doctoral student at Saarland University, Germany, said in a news release.
William Schaffner, MD, a professor in the Division of Infectious Diseases at Vanderbilt University Medical Center, Nashville, Tenn., told CBS News that same-arm vaccinations may work better because the cells that provide the immune response are in local lymph nodes.
There’s greater immunological response if the immune cells in the lymph nodes are restimulated in the same place, said Dr. Schaffner, who was not involved in the German study.
The scientists from Saarland University said more research is needed before they can be certain that having vaccinations in the same arm is actually more effective for COVID shots and sequential vaccinations against diseases such as the flu.
A version of this article first appeared on Medscape.com.