The vaccine effectiveness (VE) of Ad26.COV2.S was stable over six months, including during a period of Delta variant predominance, according to a study published online March 17 in JAMA Network Open.

Jennifer M. Polinski, ScD, MPH, from Aetion Inc. in New York City, and colleagues examined the association between receipt of Ad26.COV2.S vaccine and COVID-19-related infections and hospitalizations before and during the Delta variant surge. Data were included for 422,034 vaccinated individuals and 1,645,397 matched unvaccinated individuals. Data were obtained from March 1, 2020, through Aug. 31, 2021.

The researchers found that VE was 76% for COVID-19 infections and 81% for COVID-19-related hospitalizations. VE was stable over calendar time and for at least 180 days after vaccination. VE during June to August 2021 was 74 and 81% for infections and hospitalizations, respectively, among states with high Delta variant incidence. Higher VE for COVID-19 was seen for individuals younger than 65 years (78%), while VE was lower for immunocompromised individuals (64%). All estimates were corrected for underrecording of vaccination.

"As the COVID-19 pandemic continues and variants evolve, the observed VE may change as new variants emerge," the authors write. "Recent data have shown that a second dose will further improve protection."

Several authors disclosed financial ties to health care technology and pharmaceutical companies, including Janssen, which manufactures the Ad26.COV2.S vaccine and funded the study.