A Russian vaccine against COVID-19 — Gam-COVID-Vac (dubbed “Sputnik V”) — shows 92% efficacy in interim results from a phase 3 trial reported in The Lancet.

The two-dose vaccine uses replication-deficient adenoviruses to deliver a SARS-CoV-2 glycoprotein as the antigenic stimulus. Doses are administered at 21-day intervals, and the vaccine may be stored in normal freezers. The Moscow-based, placebo-controlled trial enlisted some 22,000 SARS-CoV-2–negative adults, about 20,000 of whom had no protocol violations and were included in the analysis.

Randomised, double-blind, placebo-controlled, phase 3 trial at 25 hospitals and polyclinics in Moscow, Russia was performed, including participants aged at least 18 years, with negative SARS-CoV-2 PCR and IgG and IgM tests, no infectious diseases in the 14 days before enrolment, and no other vaccinations in the 30 days before enrolment.

Participants were randomly assigned (3:1) to receive vaccine or placebo, with stratification by age group. Investigators, participants, and all study staff were masked to group assignment. The vaccine was administered (0·5 mL/dose) intramuscularly in a prime-boost regimen: a 21-day interval between the first dose (rAd26) and the second dose (rAd5), both vectors carrying the gene for the full-length SARS-CoV-2 glycoprotein S.

The primary outcome was the proportion of participants with PCR-confirmed COVID-19 from day 21 after receiving the first dose. All analyses excluded participants with protocol violations: the primary outcome was assessed in participants who had received two doses of vaccine or placebo, serious adverse events were assessed in all participants who had received at least one dose at the time of database lock, and rare adverse events were assessed in all participants who had received two doses and for whom all available data were verified in the case report form at the time of database lock. The trial is registered at ClinicalTrials.gov (NCT04530396).

Findings Between Sept 7 and Nov 24, 2020, 21 977 adults were randomly assigned to the vaccine group (n=16501) or the placebo group (n=5476). 19866 received two doses of vaccine or placebo and were included in the primary outcome analysis.

From 21 days after the first dose of vaccine (the day of dose 2), 16 (0·1%) of 14964 participants in the vaccine group and 62 (1·3%) of 4902 in the placebo group were confirmed to have COVID-19; vaccine efficacy was 91·6% (95% CI 85·6–95·2).

Most reported adverse events were grade 1 (7485 [94·0%] of 7966 total events). 45 (0·3%) of 16427 participants in the vaccine group and 23 (0·4%) of 5435 participants in the placebo group had serious adverse events; none were considered associated with vaccination, with confirmation from the independent data monitoring committee.

Four deaths were reported during the study (three [<0·1%] of 16 427 participants in the vaccine group and one [<0·1%] of 5435 participants in the placebo group), none of which were considered related to the vaccine. Interpretation

This interim analysis of the phase 3 trial of Gam-COVID-Vac showed 91·6% efficacy against COVID-19 and was well tolerated in a large cohort.

The authors report that, since federal approval in August 2020, more than 2 million doses of Gam-COVID-Vac have been administered to the Russian public — largely to at-risk groups.