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For multiple-dose vaccine regimens, the decision to administer the second dose in the opposite or the same limb is usually based on individual preference and anatomic factors. To evaluate if receiving the second dose of BNT162b2 COVID-19 vaccine in the opposite arm yielded different responses than receipt in the same arm, investigators analyzed binding and neutralizing antibody responses at 0.6, 8, and 14 months after the second dose in a longitudinal cohort at a medical center in Oregon. Arm choice was based on the recipient's preference, and a third vaccine dose was given between 8 and 14 months.
Among 947 participants who were seronegative at baseline (mean age, 44 years; 23% male), 507 were in the same-arm group and 440 in the opposite-arm group. Receptor binding domain antibody levels at 0.6, 8, and 14 months were 1.2-fold, 1.4-fold, and 1.4-fold higher, respectively, in the opposite-arm compared with the same-arm group. In a subset of 108 participants matched by age, gender, and vaccination and sampling times, neutralizing antibody levels against the ancestral strain were no different between groups at 0.6 months but were higher in the opposite-arm group at 8 months.
Fazli S et al. Contralateral second dose improves antibody responses to a two-dose mRNA vaccination regimen. J Clin Invest 2024 Jan 16; [e-pub]. (https://doi.org/10.1172/JCI176411)
Comment
This study has substantial limitations: Choice of arm was not randomized, SARS-CoV-2 infection status was ascertained via serology with its attendant limited sensitivity, and timing of vaccination and blood sampling was variable. In fact, a recent observational study (Ziegler et al.) arrived at the opposite conclusion. The clinical value of these findings is likely negligible, given the high prevalence of SARS-CoV-2 infections and the numerous vaccine doses received by the public. Such hypothesis-generating findings may require examination in the context of other antigens.