Interim Phase 3 Analysis: Russian COVID-19 Vaccine Shows 91.6% Efficacy

Gam-COVID-Vac, also known as Sputnik V, is a heterologous recombinant adenovirus-based SARS-CoV-2 vaccine that was well-tolerated and showed 91.6% efficacy against COVID-19 in people aged 18 years and older, according to an interim phase 3 analysis published in The Lancet.

In this randomized, double-blind, placebo-controlled, phase 3 trial (ClinicalTrials.gov identifier: NCT04530396) conducted in 25 hospitals and polyclinics in Moscow, Russia, researchers investigated whether a 2-dose Gam-COVID-Vac vaccine was safe and effective in preventing COVID-19 beginning the day of the second dose, or 21 days after the first dose. 

The final analysis included 19,866 adults (98.5% White; mean age, 45.3 years) randomly assigned in a 3:1 ratio to receive either a vaccine (n=14,964) or placebo (n=4902). These adults were stratified into 5 age groups: 18 to 30 years, 31 to 40 years, 41 to 50 years, 51 to 60 years, and over 60 years.

The participants in the vaccine and placebo cohorts were similar in age, sex, and comorbidity distribution. The median follow-up time was 48 days after the first dose (interquartile range [IQR], 39-58 days).

From the day of the second vaccine dose (day 21), 0.1% (16/14,964) of participants from the vaccine cohort and 1.3% (62/4902) of participants from the placebo group were confirmed to have COVID-19, yielding a vaccine efficacy of 91.6% (95% CI, 85.6-95.2). Vaccine efficacy was 73.1% (95% CI, 63.7-80.1) any time after dose 1, with similar rates of disease onset between the 2 cohorts until 16 to 18 days after dose 1.

A subanalysis of 2144 adults older than 60 years showed vaccine efficacy at 91.8% (95% CI, 67.1-98.3).

Immunogenicity analyses at 42 days postvaccine showed robust receptor-binding domain (RBD)-specific antibodies and virus-neutralizing antibodies. Of the 342 participants analyzed for the presence of antibodies specific to the RBD of SARS-CoV-2 glycoprotein S in the vaccine group, RBD-specific immunoglobulin G as detected in 98% of participants (geometric mean titer, 8996; 95% CI, 7610-10,635; seroconversion rate, 98.25%). Compared with the other age groups, the 18 to 30 years old age group (P =.0065) had a stronger response. 

Of the 72 participants analyzed for the presence of neutralizing antibodies in the vaccine group, the geometric mean titer was 44.5 (95% CI, 31.8-62.2) with a seroconversion rate of 95.83%.

The vaccine also induced a strong cellular immune response at 28 days postvaccine compared with day 1. Of the 44 participants in the vaccine cohort analyzed, all had significantly higher levels of IFN-γ secretion upon antigen restimulation (median, 32.77 pg/mL; IQR, 13.94-50.76).

Most reported adverse events were grade 1, and the most common were flulike illness, injection site reactions, headache, and lethargy. None of the serious adverse events were considered to be associated with vaccination. There were 4 deaths among the participants, but none were vaccine related.

The study was limited by its small sample size within the different age groups, exclusion of asymptomatic cases in the analysis, and its predominantly White population. In addition, researchers could not assess duration of protection due to the short follow-up time. The vaccine will need to be further investigated in more diverse populations, including pregnant women, immunosuppressed patients, and children and adolescents.

Although the vaccine has been approved for storage at 2 to 8 °C, this study used the liquid form of the vaccine, which requires storage at -18°C.

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.

Reference

Logunov DY, Dolzhikova IV, Shcheblyakov DV, et al; Gam-COVID-Vac Vaccine Trial Group. Safety and efficacy of an rAd26 and rAd5 vector-based heterologous prime-boost COVID-19 vaccine: an interim analysis of a randomised controlled phase 3 trial in Russia. Lancet. 2021;397(10275):671-681. doi:10.1016/S0140-6736(21)00234-8

This article originally appeared on Infectious Disease Advisor