A Beijing based company named “Sinovac Biotech” developed a new COVID 19 vaccine by growing the novel Coronavirus in the monkey cell line and inactivating it with chemicals. The vaccine consists of an old-fashioned formulations having a chemically inactivated version of the virus. Researchers gave two different doses of the vaccine to eight rhesus macaque monkeys. Three weeks later, they introduced the SARS-CoV-2 virus directly into the monkeys’ lungs through tubes down their tracheas, and none developed a full-blown infection, no obvious side effects in the monkeys were observed.
A paper published on 19 April says that those monkeys that were given the highest dosage of the vaccine gave the best response. After seven days the animals received the virus, researchers could not detect it in the lungs of any of them. Some lower dosed animals had some sort of viral blip but overall it appeared to have controlled the infection. The results “give us a lot of confidence” that the vaccine will work in humans, says Meng Weining, Sinovac’s senior director for overseas regulatory affairs.
Douglas Reed of the University of Pittsburgh said that “the number of animals was too small to yield statistically significant results.” Another concern is that monkeys do not develop the most severe symptoms that SARS-CoV-2 causes in humans. The Sinovac researchers acknowledge in the paper that “It’s still too early to define the best animal model for studying SARS-CoV-2,” but noted that unvaccinated rhesus macaques were given the virus “mimic COVID-19-like symptoms.”
Previous research with vaccines on animals showed that it causes severe acute respiratory syndrome and Middle East respiratory syndrome. But this new research did not find any evidence of lung damage in vaccinated animals who produced relatively low levels of antibodies, which “lessens the concern about vaccine enhancement,” Reed says.
In test-tube experiments, the Sinovac researchers mixed antibodies taken from monkeys, rats, and mice given their vaccine with strains of the virus isolated from COVID-19 patients in China, Italy, Switzerland, Spain, and the United Kingdom. The antibodies potently “neutralized” all the strains, which are “widely scattered on the phylogenic tree,” the researchers noted.
“This provides strong evidence that the virus is not mutating in a way that would make it resistant to a #COVID19 vaccine,” tweeted by immunologist Mark Slifka of Oregon Health & Science University.
Sinovac is an experienced vaccine maker, it could produce about 100 million doses of the vaccine and might need to partner with other makers if the company’s COVID-19 vaccine proves safe and effective in human trials. The company recently started phase I clinical trials in Jiangsu province, north of Shanghai, which aim to gauge safety and immune responses in 144 volunteers. An equal number of participants will receive the high and low doses or a placebo.
Although placebos are not typically used in phase I studies—which do not assess efficacy—Meng says this can help better evaluate whether the vaccine causes any dangerous side effects. The company hopes to start phase II studies by mid-May that have the same design but enroll more than 1000 people, with results due by the end of June. If all goes well, Meng says, Sinovac will seek to launch traditional phase III efficacy trials that compare the vaccine with a placebo in thousands of people.
According to the World Health Organization (WHO), six other vaccines had entered human trials as of April 23, and 77 other vaccines were in development stages.