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.