High-profile COVID-19 vaccines developed in Russia and China share a potential shortcoming: They are based on a common cold virus to which many people have been exposed, potentially limiting their effectiveness, some experts say
FILE PHOTO: A logo of China's vaccine specialist CanSino Biologics Inc is pictured on the company's headquarters in Tianjin, following an outbreak of the coronavirus disease , China August 17, 2020. REUTERS/Thomas Peter/File Photo
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. Several researchers have chosen alternative adenoviruses or delivery mechanisms. Oxford University and AstraZeneca based their COVID-19 vaccine on a chimpanzee adenovirus, avoiding the Ad5 issue. Johnson & Johnson’s candidate uses Ad26, a comparatively rare strain.
In China and the United States, about 40% of people have high levels of antibodies from prior Ad5 exposure. In Africa, it could be has high as 80%, experts said.In a 2004 trial of a Merck & Co Ad5-based HIV vaccine, people with pre-existing immunity became more, not less, susceptible to the virus that causes AIDS.
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