Randomised controlled trial reveals no benefit to a 3-month delay in COVID-19 mRNA booster vaccine

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Abstract

BACKGROUND. There is uncertainty around the timing of booster vaccination against COVID-19 in highly vaccinated populations during the present endemic phase of COVID-19. Studies focused on primary vaccination have previously suggested improved immunity after delaying immunisation. METHODS. We conducted a randomised controlled trial (Nov 2022 – Aug 2023) and assigned 52 fully vaccinated adults to an immediate or a 3-month delayed bivalent Spikevax mRNA booster vaccine. Follow-up visits were completed for 48 participants (n = 24 per arm), with saliva and plasma samples collected following each visit. RESULTS. The rise in neutralising antibody responses to ancestral and Omicron strains were almost identical between the immediate and delayed vaccination arms. Analyses of plasma and salivary antibody responses (IgG, IgA), plasma antibody-dependent phagocytic activity, and the decay kinetics of antibody responses were similar between the 2 arms. Symptomatic and asymptomatic SARS-CoV-2 infection occurred in 49% (21/49) participants over the median 11.5 months of follow up and were also similar between the 2 arms. CONCLUSIONS. Our data suggests no benefit from delaying COVID-19 mRNA booster vaccination in pre-immune populations during the present endemic phase of COVID-19 TRIAL REGISTRATION. Australian New Zealand Clinical Trials Registry number 12622000411741. FUNDING. National Health and Medical Research Council, Australia, Program Grant App1149990 and Medical Research Future Fund App2005544.

Authors

Wen Shi Lee, Jennifer Audsley, Mai-Chi Trieu, Arnold Reynaldi, L. Carissa Aurelia, Palak H. Mehta, Joanne Patterson, Helen E. Kent, Julie Nguyen, Thakshila Amarasena, Robyn Esterbauer, Ebene R. Haycroft, Pradhipa Ramanathan, Miles P. Davenport, Timothy E. Schlub, Joseph Sasadeusz, Adam K. Wheatley, Amy W. Chung, Jennifer A. Juno, Kevin J. Selva, Stephen J. Kent