Individuals ≥18 years, fully vaccinated with Ad26.COV2 We used de-identified claims in a research database that included vaccination status and Covid-positivity status. The purpose of this study was to evaluate the COVID mRNA based and adenovector based vaccines' differential effectiveness during the time of circulation of the Delta variant and determine what impact this would have on population health and cost effectiveness. Several vaccines with demonstrated efficacy for coronavirus disease 2019 (Covid-19) are available.