MOSCOW (Reuters) - Some of those volunteering in a trial of Russia’s second COVID-19 vaccine have broken rank and conducted go-it-alone amateur “citizen experiments” that they say raise concerns about the shot’s efficacy. A group of participants in the trial of the EpiVacCorona vaccine, developed by the Vector Institute in Siberia, have been running antibody and other tests to try to evaluate the shot, and sharing their experiences. The break-away group is led by trial volunteer Andrey Krinitsky, who is not a scientist. The group’s findings were made public in an open letter on their blog on Wednesday. The letter says some volunteers have taken commercially-available antibody tests, while others have recorded cases of COVID-19 in their group and sent frozen blood plasma samples to independent laboratories to test the vaccine’s ability to neutralise an infection. The scientists behind the vaccine, which has been approved by the Russian regulator and added to the national inoculation programme, say it is safe and effective. The trial in which the breakaway group had been taking part began in November 2020 and involves a total of 3,000 people across Russia. EpiVacCorona, Russia’s second vaccine to be registered, is a synthetic peptide vaccine which uses a different technology from the better-known Sputnik V shot. Unlike for Sputnik V, whose late-stage, Phase III trial results were published in The Lancet medical journal in February, developers of Russia’s second shot have not yet disclosed larger scale trial results. Yet more than 115,000 doses have been deployed in the national inoculation programme, according to authorities. Over 5 million doses should be ready by July. The government health watchdog supervising the development of the EpiVacCorona vaccine, rejected Krinitsky’s claims in a comment published in the RBC newspaper on Thursday. The watchdog pointed to results from early-stage, Phase I/II trials which the vaccine developers said involved 100 people and showed the shot to be 100% effective in producing antibodies “specific to the antigens that make up the vaccine”. Describing their “citizen experiments”, the open letter’s authors said they recorded 18 cases of people getting COVID-19 three weeks or more after receiving the EpiVacCorona shot. Among these were patients that required hospitalisation due to COVID-19 lung damage, they said. The group also said 139 members took antibody tests recommended by the vaccine’s developers, and 30% found no antibodies were produced. The government health watchdog did not respond to a Reuters request for comment on the letter. In its earlier response, it cited early-stage trial results and said: “Seroconversion, the body’s production of specific antibodies... to the presence of an antigen that enters the body during vaccination... was recorded in 100% of volunteers 21 days after receiving the second shot.” “We can conclude that the EpiVacCorona vaccine is an immunogenic and safe product for the prevention of COVID-19.” Out of Russia’s population of 145 million, 4.3 million people have now been fully vaccinated against COVID-19, almost all with Sputnik V, including around 1 million in the capital, according to officials.