Some 15 scientists have written to The Lancet questioning the journal’s publication of trial results for Russia’s COVID-19 vaccine, saying the similarities in patient data were improbable.

The Lancet published the results of a combined phase 1-2 trial early this month, several weeks after Russian President Vladimir Putin declared his country was the first to approve a vaccine against the virus.

The vaccine, dubbed Sputnik V and developed by the Gamaleya Research Institute of Epidemiology and Microbiology in Moscow, was administered in two separate components to 40 study participants, with each component also tested individually among 36 other participants.

The study authors said 100% of participants who received both vaccine components developed SARS-CoV-2 neutralising antibodies comparable to those in people recovered from COVID-19.