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Sinovac Biotech has created a new COVID-19 vaccine by developing the new coronavirus in the VERO monkey cell line and inactivating it with chemicals.
Xinhua / Alamy Stock Photo
By Jon Cohen
Science’s COVID-19 reports are supported by the Pulitzer Center.
For the first time, one of the many COVID-19 vaccines in development has protected an animal, rhesus macaques, from infection with the new coronavirus, scientists report. The vaccine, an outdated formulation consisting of a chemically inactivated version of the virus, produced no obvious side effects in the monkeys, and human trials began on April 16.
Researchers at Sinovac Biotech, a private company based in Beijing, gave two different doses of their COVID-19 vaccine to a total of eight rhesus macaque monkeys. Three weeks later, the group introduced SARS-CoV-2, the virus that causes COVID-19, into the monkeys’ lungs through the tubes through their tracheas, and neither developed a full-blown infection.
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The monkeys that received the highest dose of vaccine had the best response: Seven days after the animals received the virus, the researchers were unable to detect it in the pharynx or lungs of any of them. Some of the lower-dose animals had a “viral virus” but also appeared to have controlled the infection, Sinovac’s team reports in an article published April 19 on the bioRxiv preprint server. In contrast, four control animals developed high levels of viral RNA in various parts of the body and severe pneumonia. The results “give us a lot of confidence” that the vaccine will work in humans, says Meng Weining, senior director of regulatory affairs abroad at Sinovac.
“I like it,” says Florian Krammer, a virologist at the Icahn School of Medicine in Mount Sinai, co-author of a status report on the different COVID-19 vaccines in development. “This is the old school but it could work. What I like the most is that many vaccine producers, also in low- and middle-income countries, could make such a vaccine. “
But Douglas Reed of the University of Pittsburgh, which is developing and testing COVID-19 vaccines in monkey studies, says the number of animals was too small to produce statistically significant results. His team also has a manuscript in preparation that raises concerns about how Sinovac’s team increased the stock of new coronaviruses used to challenge animals: it may have caused changes that make it less reflective than those that infect humans.
Another concern is that monkeys do not develop the more severe symptoms that SARS-CoV-2 causes in humans. The Sinovac researchers acknowledge in the document that “it is still too early to define the best animal model to study SARS-CoV-2”, but noted that unvaccinated rhesus macaques receiving the virus “mimic symptoms similar to COVID-19 “
The study also addressed concerns that partial protection could be dangerous. Previous experiments in animals with vaccines against the related coronaviruses that cause severe acute respiratory syndrome and Middle East respiratory syndrome had found that low levels of antibodies could lead to aberrant immune responses when an animal received the pathogens, improving infection and causing pathology in your lungs. But Sinovac’s team found no evidence of lung damage in vaccinated animals that produced relatively low levels of antibodies, “lessening concern about improving the vaccine,” says Reed. “However, there is still a lot of work to do.”
SARS-CoV-2 appears to accumulate mutations slowly; Still, variants can pose a challenge for a vaccine. In test tube experiments, the Sinovac researchers mixed antibodies taken from monkeys, rats, and mice that received their vaccine with strains of the virus isolated from patients with COVID-19 in China, Italy, Switzerland, Spain, and the United Kingdom. The antibodies “neutralized” all the strains, which are “widely dispersed in the phylogenetic tree,” the researchers noted.
“This provides strong evidence that the virus is not mutating in a way that would make it resistant to # COVID-19 vaccine, “immunologist Mark Slifka of Oregon Health & Science University tweeted.” Good to know. “
Sinovac is an experienced vaccine manufacturer: it has marketed inactivated viral vaccines for hand, foot and mouth disease; hepatitis A and B; and H5N1 flu or avian flu. But Meng says it could produce a maximum of about 100 million doses of the vaccine and may need to partner with other manufacturers if the company’s COVID-19 vaccine is safe and effective in human trials.
The company recently began phase I clinical trials in Jiangsu province, north of Shanghai, which aims to assess safety and immune responses in 144 volunteers. An equal number of participants will receive either the high and low doses or a placebo. Although placebos are not typically used in phase I studies, which do not evaluate efficacy, Meng says this may help better assess whether the vaccine causes any dangerous side effects. The company expects to start phase II studies in mid-May that have the same design but enroll more than 1,000 people, and that the results will be ready by the end of June.
If all goes well, Meng says, Sinovac will seek to launch traditional phase III efficacy trials comparing the vaccine to a placebo in thousands of people. The company has also discussed joining international vaccine trials organized by the World Health Organization (WHO). Given the low level of transmission now occurring in China, the company is considering even more efficacy trials in other countries that are more affected by the virus. “We can’t put all of our eggs in one basket,” says Meng.
To quickly get more efficacy data after Phase I and II trials and potentially help people, Meng says Sinovac can apply to regulatory agencies in China and other countries for emergency authorization to give the vaccine to people with high risk of infection, such as customs officers and police officers who generally do not wear the protective equipment used by health workers. The Democratic Republic of the Congo in 2018 began extensively using an experimental Ebola vaccine in that state, and evidence suggests that it powerfully helped curb that epidemic. (That Ebola vaccine received regulatory approval for the first time in November 2019.)
According to the WHO, six other vaccines had entered human trials as of April 23, and another 77 were in development. The vast majority of these vaccines use modern genetic engineering tools (only four are based on outdated inactivation technology), but Meng says that what ultimately matters is whether a vaccine is safe and effective, not how it’s made. . “We are not comparing ourselves to anyone,” says Meng. “In this pandemic situation, the most important thing is to make a vaccine, no matter what type of vaccine it is, that is safe and effective as soon as possible.”
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