Allison Martell, Julie Steenhuysen
TORONTO/CHICAGO: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 Anna Durbin, a vaccine researcher at Johns Hopkins University. “I’m not sure what their strategy is … maybe it won’t have 70% efficacy. It might have 40% efficacy, and that’s better than nothing, until something else comes along.”
Vaccines are seen as essential to ending the pandemic that has claimed over 845,000 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. Neither CanSino nor Gamaleya responded to requests for comment.
“I would be worried about the use of those vaccines in any country or any population that was at risk of HIV, and I put our country as one of them,” said Dr. Larry Corey, co-leader of the U.S. Coronavirus Vaccine Prevention Network, who was a lead researcher on the Merck trial.
Gamaleya’s vaccine will be administered in two doses: The first based on Ad26, similar to J&J’s candidate, and the second on Ad5.
Alexander Gintsburg, Gamaleya’s director, has said the two-vector approach addresses the immunity issue. Ertl said it might work well enough in individuals who have been exposed to one of the two adenoviruses.
Many experts expressed skepticism about the Russian vaccine after the government declared its intention to give it to high-risk groups in October without data from large pivotal trials.
“Demonstrating safety and efficacy of a vaccine is very important,” said Dr. Dan Barouch, a Harvard vaccine researcher who helped design J&J’s COVID-19 vaccine. Often, he noted, large-scale trials “do not give the result that is expected or required.”
Source: Reuters, Additional reporting by Christine Soares in New York, Kate Kelland in London, Polina Ivanova in Moscow and Roxanne Liu in Beijing; Editing by Caroline Humer and Bill Berkrot