Immunity concern over some COVID-19 vaccines

The COVID-19 vaccines being developed in Russia and China are some of the earliest to go into production.

But scientists say they are concerned about how effective they will be given they are based on the common cold virus, which many people have already been exposed to.

China's CanSino's Biologics vaccine, approved for the military, uses a modified form of the adenovirus type 5 or Ad5. Russia's Gamaleya Institute has developed a vaccine that is also based on Ad5 and another less common adenovirus.

But experts say about 40% of people in places like China and the United States, already have high levels of antibodies from Ad5 - in Africa it could be as high as 80%. And that could be a problem.

Some scientists worry that antibodies against Ad5 could cause the immune system to attack the vector instead of responding to the coronavirus, making these vaccines less effective.

Anna Durbin from Johns Hopkins says: "TheAd5 concerns me just because a lot of people have immunity," and…"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."

There are more 150 different potential vaccines globally aiming to end the COVID-19 pandemic that's killed more than 850,000 people.

On Sunday, the head of the U.S. Food and Drug Administration said in the Financial Times they'd be willing to fast track a vaccine, authorizing it before Phase Three clinical trials are complete - as long as officials are convinced that the benefits outweigh the risks.