Earlier this month both China and Russia reported that they have developed a Covid-19 vaccine that has been clouded by doubt throughout the world since Phase III testing had not been performed. The vaccines have been developed by CanSino Biologic from China and the Gamaleya Institute in Moscow and are a modification of adenovirus type 5 (AD5). AD5 is currently being used to treat the common cold, and scientists and researchers are now concerned with the effectiveness of the vaccine.
Vaccine developers at CanSino Biologic and the Gamaleya Institute have years of experience, including an approved Ebola vaccine based on Ad5. Medical researchers have experimented with Ad5-based vaccines to combat a variety of infections for decades, including tuberculosis and SARS. The Ad5 vaccines employ harmless viruses as vectors to ferry genes from the target virus into human cells, which prompts an immune response to fight the virus.
The issue currently is that many people already have antibodies against Ad5, which may cause the immune system to attack the vector rather than attack the virus, causing the vaccine to be less effective. Anna Durbin, a vaccine researcher at Johns Hopkins University stated, “The Ad5 concerns me just because a lot of people have immunity. I am 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.” It is believed that 40% of people in the United states have high levels of antibodies from prior Ad5 exposure.