No serious adverse events were deemed to be associated with vaccination, and most reported adverse events were mild, including flu-like symptoms, pain at the injection site and weakness or low energy.
Interim data from the phase three trial of Sputnik V suggests a two-dose regimen induces the same high levels of efficacy seen in the mRNA vaccines developed by Pfizer/BioNTech and Moderna, and is similarly effective in providing protection among those aged over 60.
The preliminary findings, published in The Lancet, are based on analysis of data from nearly 20,000 participants, three-quarters of whom received the vaccine and one-quarter received a placebo.
The results help to alleviate any lingering concern surrounding Sputnik V, which was first granted state approval in August – before phase three testing.
Authorities notably singled out teachers, as well as doctors, to receive the first available doses of the vaccine, long before the study had been concluded.
The move drew intense scepticism from the international scientific community, leading to claims that Moscow had jumped the gun in pursuit of political gains. Experts both at home and abroad warned against its wider use until the studies were completed.
But confirmation of Sputnik V’s efficacy and safety has been widely welcomed, with the phase three trial ongoing and further analysis expected in the near future.
“Despite the earlier misgivings about the way this Russian Sputnik V vaccine was rolled out more widely – ahead of sufficient phase three trial data – this approach has been justified to some extent now,” said Dr Julian Tang, a virologist at the University of Leicester.
“Such pandemic-related vaccine rollout compromises have, to be fair, been adopted in the UK vaccination programme also.”
Alexander Edwards, an associate professor in biomedical technology at the University of Reading, said: “The vaccine trial results are coming thick and fast as high infection rates in areas where phase three clinical trials [are being run] provide increasing amounts of data.”
Sputnik V combines two adenovirus vectors – recombinant human adenovirus type 26 (rAd26-S) and recombinant human adenovirus type 5 (rAd5-S) – which have been modified to express the Sars-Cov-2 spike protein.
The adenoviruses are also weakened so that they cannot replicate in human cells and cannot cause disease.
In the trial, participants were given one dose of rAd26-S, followed by a booster dose of rAd5-S 21 days later.
According to the researchers, using a different adenovirus vector for the booster vaccination may help create a more powerful immune response, compared with using the same vector twice.
They suggest this is because it minimises the risk of the immune system developing resistance to the initial vector.
Dr Inna V Dolzhikova, co-lead author, from the Gamaleya National Research Centre for Epidemiology and Microbiology in Russia, said: “Our interim analysis of the randomised, controlled, phase three trial of Gam-Covid-Vac in Russia has shown high efficacy, immunogenicity, and a good tolerability profile in participants aged 18 years or older.”
Between 7 September and 24 November last year, a total of 21,977 adults were randomly assigned to receive the vaccine (16,501) or placebo (5,476).
14,964 participants in the vaccine group and 4,902 in the placebo group received two doses of the vaccine or placebo and were included in the primary interim efficacy analysis reported on Tuesday.
From 21 days after receiving the first dose – the day of the second dose – 16 cases of symptomatic Covid-19 were confirmed in the vaccine group, and 62 cases in the placebo group, equivalent to an efficacy of 91.6 per cent.
Researchers say the vaccine induced a robust antibody response and T-cell response with data from 342 and 44 participants respectively.
Six of the 342 participants did not mount an immune response following vaccination, possibly due to older age or individual characteristics, according to the study.
The authors note that because Covid-19 cases were detected only when participants self-reported symptoms, followed by a test, the efficacy analysis only includes symptomatic cases of the virus.
They say further research is needed to understand the efficacy of the vaccine on asymptomatic Covid-19, and transmission.
The median follow-up was 48 days from the first dose, so the study cannot assess the full duration of protection.
Additional reporting by PA
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