Effectiveness of the mRNA-1273 Vaccine during a SARS-CoV-2 Delta Outbreak in a Prison
Elizabeth T. Chin, David Leidner, Yifan Zhang, Elizabeth E. Long, Lea Prince, Ying Li, Jason R. Andrews, David M. Studdert, Jeremy D. Goldhaber‐Fiebert, Joshua A. Salomon
Abstract
Effectiveness of the mRNA-1273 Vaccine during a SARS-CoV-2 Delta Outbreak in a PrisonTo the Editor: The mRNA vaccines have been shown to be highly effective in preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and associated illness, 1,2 although recent reports suggest reduced effectiveness against infection with the B.1.617.2 (or delta) variant. 3,4We assessed the effectiveness of the mRNA-1273 (Moderna) vaccine among incarcerated men during a coronavirus disease 2019 (Covid-19) outbreak that was dominated by transmission of the delta variant.The Sierra Conservation Center (SCC), in Jamestown, California, is a low-to-medium security prison for men.No SARS-CoV-2 infections were detected among residents between April 23 and July 15, 2021.A substantial outbreak began on July 16, which resulted in 15% of the exposed population becoming infected by August 15, 2021 (Fig. S1 in the Supplementary Appendix, available with the full text of this letter at NEJM .org).The delta variant was identified in all 13 successfully sequenced positive samples that had been obtained from SCC residents from July 16 to July 21, 2021.The delta variant was also identified in all 6 successfully assayed positive samples obtained from SCC staff during this period.We tracked infections over a 30-day period (July 16 to August 15, 2021) among SCC residents who had close exposure during that time; close exposure was defined as residence in a housing unit in which at least one case had been detected.Our goal was to estimate vaccine effectiveness against SARS-CoV-2 infection (with infection confirmed by means of polymerasechain-reaction or antigen test) and symptomatic infection, defined as a case involving symptoms observed by prison health care staff or objective signs of fever (a temperature of 37.8C) or hypoxemia (an oxygen saturation of <94%) within 3 days before to 10 days after the collection date of a sample that tested positive.The mRNA-1273 vaccine accounted for 75% of all vaccines administered to SCC residents as of July 16, 2021.Residents who were fully vaccinated with the mRNA-1273 vaccine (i.e., had received a second dose at least 14 days previously) were matched with unvaccinated controls with the use of propensity scores (details are provided in the Supplementary Appendix).Vaccine effectiveness was calculated as one minus