An Observational Prospective Cohort Study of Vaccine Effectiveness Against Severe Acute Respiratory Syndrome Coronavirus 2 Infection of an Aerosolized, Inhaled Adenovirus Type 5–Vectored Coronavirus Disease 2019 Vaccine Given as a Second Booster Dose in Guangzhou City, China

Abstract Using a prospective, observational cohort study during the post–“dynamic COVID-zero” wave in China, we estimated short-term relative effectiveness against Omicron BA.5 infection of inhaled aerosolized adenovirus type 5–vectored ancestral strain coronavirus disease 2019 (COVID-19) vaccine as a second booster dose approximately 1 year after homologous boosted primary series of inactivated COVID-19 vaccine compared with no second booster. Participants reported nucleic acid or antigen test results weekly until they tested positive or completed predesignated follow-up. After excluding participants infected