Scientists see downsides to top Covid-19 vaccines from Russia, China

COVID-19 | 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...