Scientists have found that recently-approved coronavirus vaccines from Russia and China share a potential downfall. This would be in terms of their effectiveness due to the fact that they are developed based on a common cold virus that many people are already exposed and immune to.

According to a report, these vaccines are developed by China's Cansino Biologics and Moscow's Gamaleya Institute. While both vaccines are based on an adenovirus type 5 or Ad5, the latter is paired with a second less common adenovirus type 26 or Ad26.

After being approved for military use in China, the Wall Street Journal reported last week that Cansino Biologics' vaccine is already in talks to get approved for emergency use in several cities of Saudi Arabia like Riyadh and Mecca.

On one hand, several experts like Anna Durbin of Johns Hopkins University expressed concerns regarding the fact that many people have already developed immunity to Ad5 from previous exposures. Durbin estimates that there may be around 40% efficacy and that it could buy some time while the world is still waiting for a better vaccine to come along.

Gamaleya, on the other hand, said that its two-virus approach will resolve the Ad5 immunity issue as Ad26 is a rarer strain. For decades, several experiments have been done in vaccines based on Ad5 to treat infections but none of the proposed vaccines are widely used. What they do is they use harmless viruses as a way to transport genes from the target virus into human cells in order to trigger an immune response against the actual virus.

This resulted to a history of exposure to most people who may have already developed antibodies against Ad5 - leaving the vaccine less effective. Due to this issue of immunity, researchers from many institutions and organizations have been looking for alternatives to the Ad5 method.

Meanwhile, an inhaled Ad5 coronavirus vaccine is being developed by Dr. Zhou Xing who comes from Canada's McMaster University during her time with Cansino Biologies. Xing said that according to his assessment, the Oxford Vaccine is likely to have better chances of being approved.

Dr. Hildegund Ertl, who is the director of the Philadelphia-based at Wistar Institute Vaccine Center, said that the Ad5 vaccine could have better chances of getting a good immunity on people who have not yet developed antibodies to the vaccine.

It can be recalled that a trial conducted by Merck & Co found that people with previously-developed immunity could become more at risk of contracting HIV - a virus that attacks cells that help the body fight infection.

Further, Dr. Anthony Fauci, who is America's top infectious disease expert has said in a 2015 paper that the side-effect of the Ad5-based vaccine could only be limited to HIV vaccines.

Amid criticism expressed by several scientists, Gamaleya's director, Alexander Gintsburg, said that the two-vector approach of the Russian vaccine would be effective on people who have been exposed to one of the two adenoviruses used - Ad5 and Ad26.

Discussion about the Cuba's life-saving lung cancer vaccine called CimaVax-EGF is growing rapidly. REUTERS/Eric Gaillard

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