DISCUSSION
This is the first clinical study to evaluate the safety and immunogenicity of the mRNA-1273 COVID-19 vaccine booster when coadministered with RZV or when administered sequentially. As with sequential administration, coadministration elicited robust anti-gE and anti-S antibody responses, with MGIs exceeding 34-fold and 16-fold, respectively. Notably, in terms of these humoral immune responses, coadministration of the vaccines proved to be noninferior to their sequential administration, confirming an absence of evidence for immune interference upon coadministration. The validity of this result is further strengthened by the same observation of noninferiority from analysis on the exposed set. Although for both RZV and mRNA-1273, no validated immunologic mechanistic correlate of protection has been established to date, there is evidence that anti-gE and anti-S antibody responses, as measured in this study, can be considered as reasonable surrogate endpoints likely to predict clinical efficacy for these respective vaccines [The reactogenicity and safety profile of mRNA-1273 and RZV1 coadministration was within their respective Reference Safety Information [Potential limitations of the study include the open-label design, which could have influenced safety reporting and causality assessments, although this would be expected to be biased against the Coad group. Coadministration of mRNA-1273 was only assessed post-RZV1; however, since reactogenicity is similar following RZV1 or RZV2 [In conclusion, the results of this study have shown no safety concerns and a lack of immunologic interference when a booster dose of the COVID-19 mRNA-1273 vaccine was coadministered with the adjuvanted RZV in adults aged ≥50 years. These results provide important data that were previously lacking, to support both the public health agencies whose guidance to healthcare providers has been that COVID-19 vaccines can be administered without regard to timing of other age-appropriate vaccines and those that are awaiting such data to make evidence-based and unreserved recommendations [