On September 4, 2020, in The Lancet, Lagunov et al. published a peer reviewed study entitled "Safety and immunogenicity of an rAd26 and rAd5 vector-based heterologous prime-boost COVID-19 vaccine in two formulations: two open, non-randomised phase 1/2 studies from Russia". The article concludes,
these data collectively show that the heterologous vaccine based on rAd26-S and rAd5-S is safe, well tolerated, and does not cause serious adverse events in healthy adult volunteers. The vaccine is highly immunogenic and induces strong humoral and cellular immune responses in 100% of healthy adult volunteers, with antibody titres in vaccinated participants higher than those in convalescent plasma.
Though these results are based on limited sample sizes, Bloomberg greeted the news positively, with the headline "Russia’s Covid Vaccine Shows Potential in Peer Review, Lancet Reports".