The vaccines registered in Russia and China may have a common flaw that could reduce their effectiveness, Western scientists warned. The fact is that vaccines are based on a fairly common adenovirus, and many people may be immune to it.

The coronavirus vaccines developed in Russia and China may have a common flaw that potentially reduces their effectiveness, Reuters writes, citing Western scientists. In their opinion, the problem lies in the fact that the developers, the Chinese company CanSino and the Gamaleya Research Center for Epidemiology and Microbiology in Russia, have developed a vaccine based on adenovirus type 5 (Ad5), to which many people may have antibodies, the agency writes.

“Ad5 worries me because a lot of people are immune to it,” Anna Durbin, a Johns Hopkins University vaccine researcher, told Reuters. "I don't understand what their [vaccine developers] strategy is." According to her, the use of such vaccines will not give 70% efficiency: "Maybe 40% - which, of course, is better than nothing, there is nothing else yet."

The Russian vaccine uses not only Ad5, but also the less common Ad26 strain. The Gamaleya Center stated that the use of two types of viruses is precisely the solution to the "Ad5 problem" that Durbin is talking about, according to Reuters. The Russian Direct Investment Fund (RDIF) also writes on its website that vaccination with injections of two human adenoviruses (two vectors) in two stages "has a clear advantage" over vaccines with one adenovirus (single-vector), such as CanSino or Johnson & Johnson, which uses only Ad26. RDIF invested in the development of a vaccine at the Gamaleya.

"I think they [developers of Ad5 vaccines] will achieve good immunity in people who do not have antibodies to the vaccine itself, but many do," Hildegund Ertl, director of the vaccine center at the Wistar Institute in Philadelphia said. She noted that the two-way vaccine may be effective in people who have contracted one of the two adenoviruses used.

Western companies have chosen other adenoviruses or methods of delivering coronavirus genes into cells as a solution, Reuters continues. As an example, the agency cites the "relatively rare" adenovirus Ad26 in the development of Johnson & Johnson, as well as the Oxford University and AstraZeneca vaccine based on the chimpanzee adenovirus.

The "Oxford" vaccine has an advantage over the development of the Chinese CanSino, Zhou Xing, an employee of the Canadian McMaster University said. He drew attention to the fact that the CanSino vaccine can cause fever, which only increases the mistrust of the development. In the US and China, about 40% of people have high levels of antibodies after having Ad5 disease in the past, Reuters added. In Africa, this figure can go up to 80%.

Another concern of experts is that an Ad5-based vaccine could increase the chances of contracting HIV, Reuters writes. This is due to trials of an HIV vaccine in 2004, during which people with existing Ad5 immunity became more vulnerable to HIV. At the same time, in 2015, a group of scientists suggested that this effect is associated precisely with HIV vaccines, but noted the need for additional research.

Western companies and experts have repeatedly expressed doubts about the Russian vaccine due to the pace of its approval by regulators. In particular, Western pharmaceutical companies paid attention to the fact that the vaccine, before registration, passed only the first two stages of clinical trials, although it is on the third stage that the efficacy and possible side effects are tested on large groups of people. Moreover, the results of the first rounds were not published in scientific journals. Developers of the Russian vaccine and government officials objected that the vaccine had shown safety and efficacy, and the third stage of testing would be combined with the use of the vaccine for the most vulnerable groups of the population. The head of RDIF, Kirill Dmitriev, said that an information war was being waged against the Russian vaccine. Dmitriev himself said that he had tested  himself in June the vaccine that the Gamaleya Center had developed. One of the daughters of Vladimir Putin was also vaccinated with the Russian vaccine against coronavirus.