Long-term safety and efficacy of COVE study open-label and booster phases

Vaccination with two injections of mRNA-1273 (100-μg) was shown to be safe and efficacious at preventing coronavirus disease 2019 (COVID-19) in the Coronavirus Efficacy (COVE) trial at completion of the blinded part of the study. We present the final report of the longer-term safety and efficacy data of the primary vaccination series plus a 50-μg booster dose administered in Fall 2021. The booster safety profile was consistent with that of the primary series. Incidences of COVID-19 and severe COVID-19 were higher during the Omicron BA.1 than Delta variant waves and boosting versus non-boosting was associated with significant reductions for both. In an exploratory Cox regression model adjusted for time-varying covariates, a longer interval between primary vaccination and boosting was associated with a significantly lower incidence of COVID-19 during the Omicron BA.1 wave. Boosting elicited greater immune responses against ancestral SARS-CoV-2 than the primary series, irrespective of prior SARS-CoV-2 infection. ClinicalTrials.gov: NCT04470427