The Lancet Infectious Diseases presents a significant vaccine trial conducted amidst challenging pandemic circumstances, addressing pressing national, regional, and global policy questions regarding pragmatic trials, policy decisions, and planning. Researchers focused on adults previously vaccinated with two doses of inactivated COVID-19 vaccine, randomly assigning them to receive boosters in different groups, including homologous and heterologous options. The study examined neutralizing and binding antibody titres in relation to the ancestral virus and the delta variant, primarily comparing full-dose and half-dose recipients. Results indicated similar responses across all groups, with minor adverse events observed to be lower in the half-dose recipients. Crucial remaining questions revolve around the duration of immune responses, especially in regard to cell-mediated immunity, and the need for follow-up studies in different populations and against emerging variants. The trial highlights the importance of pragmatic, cross-platform investigations for shaping effective vaccination strategies.

“Crucial questions remaining are the longevity of sustained immune responses to fractionation, including through cell-mediated immunity. Even full-dose repeat-boosted regimens have not provided prolonged protection. Follow-up of this cohort to report relative incidence of clinical outcomes, although underpowered, will be useful. Specific examination of potentially immune senescent older adults, or of children would also be useful, and of course the findings will need replication in the omicron era. Second-generation vaccines are in development that aim to broaden protection in variant-independent ways, or to target mucosal immunity and hopefully reduce transmission (although the methodological challenges are far from trivial), and that provide sustained defense against severe disease and prolonged protection from infection. These vaccines will also need to be subjected to pragmatic trials in immunologically experienced populations. These are precisely the kinds of trials we need, cross-platform, pragmatic, and policy minded. The foresight of the Indonesian Ministry of Health who sponsored the trial is to be applauded.”1

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References

  1. Bar-Zeev, N., & Ndeketa, L. (2023). Pragmatic trials to inform policy decisions and planning. The Lancet Infectious Diseases, 23(5). https://doi.org/10.1016/s1473-3099(22)00830-1

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