Effect of time-of-day vaccination on the antibody response to mRNA and protein COVID-19 vaccine in adults

Time-of-day vaccination has been suggested as a feasible method to boost COVID-19 vaccine immunogenicity particularly in high-risk groups. However, several studies report inconsistent findings. We explored if time-of-day vaccination influences antibody responses to a fourth dose of mRNA (Moderna bivalent vaccine; mRNA-1273.214/mRNA-1273.222) or protein (Novavax; NVX-CoV-2373) COVID-19 vaccine as part of a randomised controlled trial (RCT) in Melbourne, Australia. Furthermore, we assessed if time-of-day vaccination effects differed by vaccine type or sex. At day 28 post-vaccination, antibody responses to all SARS-CoV-2 variants tested were higher for morning compared to afternoon vaccination in the Moderna group. Males in the Moderna group responded with higher antibodies to all SARS-CoV-2 variants tested after morning vaccination while responses in females were unaffected by time-of-day vaccination. Time-of-day vaccination had no effect on the response to Novavax, regardless of sex. Larger randomised trials are needed to confirm these findings to optimise vaccine timing strategies.