Sequential vaccines, like those used for COVID-19, may elicit a greater immune response if the recipient has the same arm injected, called ipsilateral vaccination, as opposed to contralateral vaccination, in which the primary vaccination is delivered in one arm and booster dose is delivered to the opposite. The research is published in EBioMedicine.
German scientists tested immune response and ipsilateral versus contralateral vaccination by looking at data from 303 people who received the Pfizer-BioNTech COVID mRNA vaccine. None participants had not contracted COVID-19 prior to vaccination.
Antibody levels were measured 2 weeks after the second dose in 147 participants who received the second dose of COVID-19 vaccine in the same arm as the first, and 156 who got the second shot in the opposite arm. A subgroup of 143 individuals (64 ipsilateral, 79 contralateral) was analyzed for spike-specific CD4 and CD8 T-cells using flow cytometry, the authors said.
Median spike-specific immunoglobulin levels did not differ between the two groups, but neutralizing activity was significantly lower after contralateral vaccination. The number of cytotoxic CD8+ T cells, known as killer T cells, were detected in 67% of same-arm participants, compared to just 43% of the contralaterally vaccinated subjects.