FRIDAY, April 23, 2021 (HealthDay News) — A single dose of human adenovirus type 26 vector encoding full-length severe acute respiratory syndrome coronavirus 2 spike protein (Ad26.COV2.S) protects against moderate- to severe-critical and severe-critical COVID-19, according to a study published online April 21 in the New England Journal of Medicine.

Jerald Sadoff, M.D., from Janssen Vaccines and Prevention in Leiden, Netherlands, and colleagues randomly assigned adults to receive a single dose of either Ad26.COV2.S or placebo in an international randomized trial (19,630 received Ad26.COV2.S and 19,691 received placebo in the per-protocol population) to examine efficacy against moderate- to severe-critical COVID-19.

The researchers found that Ad26.COV2.S protected against moderate- to severe-critical COVID-19 with onset at least 14 days after administration (efficacy, 66.9 percent) and at least 28 days after administration (66.1 percent). Higher vaccine efficacy was seen against severe-critical COVID-19 (76.7 and 85.4 percent for onset at ≥14 days and at ≥28 days, respectively). Vaccine efficacy was 52.0 and 64.0 percent, respectively, against moderate- to severe-critical COVID-19 with onset at ≥14 days and at ≥28 days after administration among cases in South Africa; 94.5 percent of these cases had the 20H/501Y.V2 variant. Efficacy against severe-critical COVID-19 was 73.1 and 81.7 percent, respectively. Compared with placebo, reactogenicity was higher with Ad26.COV2.S, but was mainly mild to moderate and transient. Between the groups, the incidence of serious adverse events was balanced. Three and 16 deaths occurred in the vaccine and placebo groups, respectively (none and five, respectively, were COVID-19-related).

“The single-dose schedule and favorable storage conditions of this vaccine provide major advantages in its deployment and effect worldwide,” the authors write.

The study was funded by Janssen Research and Development, an affiliate of Janssen Vaccines and Prevention and part of the Janssen pharmaceutical companies of Johnson & Johnson.

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