Durability of Protection Against Coronavirus Disease 2019 (COVID-19) Through the Delta Surge for the NVX-CoV2373 Vaccine

Background Protein-based vaccines for coronavirus disease 2019 (COVID-19) provide a traditional vaccine platform with long-lasting protection for non–severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pathogens and may complement messenger RNA vaccines as a booster dose. While NVX-CoV2373 showed substantial early efficacy, the durability of protection has not been delineated. Methods The PREVENT-19 vaccine trial used a blinded crossover design; the original placebo arm received NVX-CoV2373 after efficacy was established. Using novel statistical methods that integrate surveillance data of circulating strains with post-crossover cases, we estimated placebo-controlled vaccine efficacy and durability of NVX-CoV2373 against both pre-Delta and Delta strains of SARS-CoV-2. Results Vaccine efficacy against pre-Delta strains of COVID-19 was 89% (95% CI, 75–95%) and 87% (72–94%) at 0 and 90 days after 2 doses of NVX-CoV2373, respectively, with no evidence of waning (P = .93). Vaccine efficacy against the Delta strain was 88% (71–95%), 82% (56–92%), and 77% (44–90%) at 40, 120, and 180 days, respectively, with evidence of waning (P < .01). In sensitivity analyses, the estimated Delta vaccine efficacy at 120 days ranged from 66% (15–86%) to 89% (74–95%) per various assumptions of the surveillance data. Conclusions NVX-CoV2373 has high initial efficacy against pre-Delta and Delta strains of COVID-19 with little evidence of waning for pre-Delta strains through 90 days and moderate waning against Delta strains over 180 days.