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’ ( 6185.HK ) 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, […]