TORONTO / CHICAGO (Reuters) – High-profile COVID-19 vaccines developed in Russia and China share a potential drawback: They are based on the common cold virus, to which many people have been exposed, potentially limiting their effectiveness, some experts say. .
PHOTO PHOTO: Logo of Chinese Vaccine Specialist CanSino Biologics Inc is depicted at the company’s headquarters in Tianjin after the outbreak of coronavirus disease (COVID-19), China, August 17, 2020. REUTERS / Thomas Peter / File Photo
The CanSino Biologics vaccine, approved for military use in China, is a modified form of type 5 or Ad5 adenovirus. The company is in talks for urgent approval in several countries before completing large-scale tests, the Wall Street Journal reported last week.
The vaccine, developed by Moscow’s Gamaleya Institute and approved in Russia earlier this month, despite limited testing, is based on Ad5 and a second less common adenovirus.
“Ad5 only applies to me 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 be 70% effective. There can be 40% efficiency and this is better than nothing until something else comes along. ”
Vaccines are thought to be essential to ending the pandemic, which has claimed more than 845,000 lives worldwide. Gamaleya said her bi-viral approach would address Ad5’s immunity issues.
Both developers have years of experience and approved Ad5-based Ebola vaccines. Neither CanSino nor Gamaleya responded to requests for comment.
Researchers have been experimenting with Ad5-based vaccines against various infections for decades, but none are widely used. They use harmless viruses as “vectors” to ferment genes from the target virus – in this case the new coronavirus – into human cells, prompting an immune response to fight the actual virus.
But many people already have antibodies to Ad5, which can cause the immune system to attack the vector instead of reacting to the coronavirus, making these vaccines less effective.
Several researchers have chosen alternative adenoviruses or delivery mechanisms. Oxford University and AstraZeneca base their COVID-19 vaccine on chimpanzee adenovirus, avoiding the Ad5 problem. The Johnson & Johnson candidate uses Ad26, a relatively rare strain.
Dr. Zhou Xing, of McMaster University in Canada, is working with CanSino on his first Ad5-based TB vaccine in 2011. His team is developing an inhaled vaccine for Ad5 COVID-19, theorizing that it can work around existing problems with immunity.
“The vaccine candidate in Oxford has a lot of an advantage over the injected CanSino vaccine,” he said.
Singh also worries that high doses of the Ad5 vector in the CanSino vaccine could cause fever, fueling the skepticism of the vaccine.
“I think they’ll get good immunity in people who don’t have antibodies to the vaccine, but a lot of people do,” said Dr. Hildegund Ertl, director of the Wistar Vaccination Center in Philadelphia.
In China and the United States, about 40% of people have high levels of antibodies from previous exposure to Ad5. In Africa, it could reach 80%, experts said.
Some researchers are also worried that the Ad5-based vaccine may increase the chances of contracting HIV.
In a 2004 study of an HIV vaccine based on Merck & Co Ad5, people with previous immunity became more, no less susceptible to the AIDS virus.
Researchers, including America’s top infectious disease expert, Dr. Anthony Fauci, said in a 2015 report that the side effect is likely to be unique to HIV vaccines. But they warned that the incidence of HIV should be monitored during and after trials of all Ad5-based vaccines in at-risk populations.
“I would worry about the use of these vaccines in any country or population at risk of HIV, and I put our country as one of them,” said Dr. Larry Corey, co-leader of the U.S. Coronavirus Vaccine Network, who was a leader. researcher in the Merck process.
The Gamaleya vaccine will be given in two doses: the first based on Ad26, similar to the J&J candidate, and the second on Ad5.
Alexander Ginzburg, director of Gamaleya, said the two-pronged approach focused on the problem of immunity. Ertl said it may work well enough in people who have been exposed to one of the two adenoviruses.
Many experts have expressed skepticism about the Russian vaccine after the government announced in October its intention to give it to high-risk groups without data from major key trials.
“Demonstrating the safety and efficacy of the vaccine is very important,” said Dr. Dan Baruch, a Harvard vaccine researcher who helped design J&J’s COVID-19 vaccine. Often, he noted, large-scale trials “do not produce the result that is expected or required.”
Additional reports by Christine Soares in New York, Kate Keland in London, Polina Ivanova in Moscow and Roxanne Liu in Beijing; Edited by Caroline Humer and Bill Bercrot