Science,Health : Scientists see downsides to high-profile Covid-19 vaccines from Russia, China

Scientists see downsides to high-profile Covid-19 vaccines from Russia and China.

CHICAGO (REUTERS)

High-profile Covid-19 vaccines developed in Russia and China share a potential shortcoming: They are based on a common cold virus that many people have been exposed to, potentially limiting their effectiveness, some experts say.

CanSino Biologics' vaccine, approved for military use in China, is a modified form of adenovirus type 5, or Ad5.

The company is in talks to get emergency approval in several countries before completing large-scale trials, the Wall Street Journal reported last week.

A vaccine developed by Moscow's Gamaleya Institute, approved in Russia earlier this month despite limited testing, is based on Ad5 and a second less common adenovirus.

"The Ad5 concerns me just because a lot of people have immunity," said Dr Anna Durbin, a vaccine researcher at Johns Hopkins University. "I'm not sure what their strategy is... Maybe it won't have 70 per cent efficacy. It might have 40 per cent efficacy, and that's better than nothing, until something else comes along."

Vaccines are seen as essential to ending the coronavirus pandemic that has claimed over 846,000 lives worldwide.Gamaleya has said its two-virus approach will address Ad5 immunity issues.

Both developers have years of experience and approved Ebola vaccines based on Ad5.

Researchers have experimented with Ad5-based vaccines against a variety of infections for decades, but none are widely used. They employ harmless viruses as "vectors" to ferry genes from the target virus - in this case the coronavirus - into human cells, prompting an immune response to fight the actual virus.



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