Modified common cold viruses are being used to create COVID-19 vaccine candidates in China and Russia. Such viruses have been studied for over 30 years, but are still not widely used. They are now driving the vaccine research from Russia’s Gamaleya Institute and China’s CanSino Biologics.
Adenovirus type 5 (Ad5)
The COVID-19 vaccine candidates are called adenovirus vector vaccines. They use modified adenovirus type 5, or Ad5, viruses. Unlike most viruses, modified viruses will not cause infection because they cannot reproduce on their own.
Ad5 viruses can be used as vectors to carry genes from the virus that causes COVID-19 into the body. The human cells will then create proteins to activate the body’s natural defenses to guard against the virus.
Has Ad5 been successful in the past?
In the 1970s, Frank Graham of Canada was the first researcher to work with Ad5 viruses. At the time, he was working at a laboratory in The Netherlands.
Graham planned to use the viruses to study natural processes responsible for cancer. He also wanted to provide the human kidney cell line that makes them, called HEK293, to researchers all over the world.
“The cells became tremendously widespread and popular” among researchers, said Graham, who is now retired and lives in Italy.
In early gene therapy, Ad5 vectors were tested to replace a missing or damaged gene. Researchers stopped using them after an 18-year-old died in 1999 when the patient’s natural defense system overreacted. The patient had received a large dose of Ad5 vectors during a gene therapy test. However, they believe much smaller doses would have been a good choice to use in developing a vaccine.
At McMaster University in Canada, Graham and other researchers developed several Ad5 vectors, including one for a rabies vaccine used on wild raccoons. They began developing an Ad5-based vaccine against Severe Acute Respiratory Syndrome (SARS) in 2003 and published early test results. The project was set aside when the SARS outbreak ended.
COVID-19 vaccine with Ad5 in China, Russia
In 2011, CanSino Biologics developed an experimental tuberculosis vaccine based on Ad5 from the McMaster researchers. The Chinese company then turned its attention to an Ad5-based Ebola vaccine at the request of the Chinese military. The Ebola vaccine was approved for military use in 2017.
In June of this year, the Chinese military approved emergency use of CanSino’s COVID-19 vaccine without Phase 3 testing. Under Phase 3 trials, an experimental vaccine is tested on tens of thousands of volunteers to measure its effectiveness.
The Gamaleya Research Institute, which developed Russia’s coronavirus vaccine, also used Ad5 vectors to develop an Ebola vaccine. The institute said that vaccine has been given to about 2,100 people.
For COVID-19, Russian researchers are combining Ad5 with another modified adenovirus called Ad26.
On August 11, Russian President Vladimir Putin announced that his country was the first to approve a vaccine for COVID-19. The approval came less than two months after the start of human testing of the vaccine. And the treatment has yet to complete Phase 3 trials.
Scientists around the world have questioned whether its quick approval without extensive testing will lead to a safe vaccine.
I'm Jonathan Evans.
Hai Do wrote this story for Learning English with additional reporting from Reuters. George Grow was the editor.
Words in This Story
modify - v. to change some parts of something while not changing other parts
vector - n. a virus that carries germs that cause disease
therapy - n. the treatment
dose - n. the amount of medicine or drug taken at one time
outbreak - n. a sudden start or increase of disease