China has five COVID-19 vaccines in clinical trials. Now one of them, from state-owned Sinopharm, has reported positive results from animal tests.
The vaccine candidate, dubbed BBIBP-CorV and made from an inactivated form of the virus, induced high levels of neutralizing antibodies against SARS-CoV-2—the virus behind COVID-19—in rodents, rabbits and monkeys without triggering any serious adverse events, a team of Chinese researchers reported in the journal Cell.
A multi-arm phase 1/2 trial examining the vaccine’s safety, as well as antibody and cellular immunity at three different dosing strengths, is ongoing, according to China’s clinical trial registry.
To make the vaccine, scientists at Sinopharm subsidiary CNBG’s Beijing Institute of Biological Products picked one viral strain from a patient that showed an optimal ability to replicate.
In mice, the researchers detected neutralizing antibodies that could block the virus from infecting host cells in all animals after immunization with the vaccine at three different dose levels. But the immunogenicity of a three-dose regimen was higher than that of both the one- and two-dose programs, according to the team.
The researchers went on to evaluate the vaccine in rhesus macaques with SARS-CoV-2, the virus that causes COVID-19. All monkeys that got a dummy shot showed a high viral load after the virus challenge. In contrast, the viral load in throat swabs was significantly lower in animals that got the low dose of the vaccine, and undetectable in those that received the higher dose.
Moreover, no immunized monkeys had a detectable viral load in their lungs, “demonstrating the BBIBP-CorV vaccination could efficiently block the infection of SARS-CoV-2 and COVID-19 disease in monkeys,” the researchers wrote in the study.
Inactivated vaccines are widely used to prevent infectious diseases such as the seasonal flu. As the researchers observed in their current study, it’s a tried-and-true vaccine technology. Nevertheless, when the Trump administration selected five vaccine projects for its Operation Warp Speed, it failed to include an inactivated vaccine.
Before BBIBP-CorV, three other COVID-19 vaccine candidates had reported protection data in rhesus monkeys: the AstraZeneca-partnered recombinant vaccine from the University of Oxford, a DNA vaccine from Harvard Medical School and Johnson & Johnson, and shot from China’s Sinovac Biotech that's also made from the inactivated virus.
The adenovirus-based recombinant technology allows easy genetic modification to make the vaccine, and it can induce potent immune responses, but the body’s pre-existing immunity to the virus used as a vector can pose a challenge.
China’s CanSino Biologics is currently leading the COVID-19 vaccine development efforts with an adenovirus-based shot. But in that vaccine’s phase 1 trial, about half of the participants came into the study with neutralizing antibodies against the Ad5 vector, which “compromised” the immune response triggered by the vaccine.
In a monkey trial of the AZ-Oxford shot, now known as AZD-1222, 5 of 6 lung lobes in the vaccinated group showed a detectable viral load, although no animal developed pneumonia.
That said, inactivated vaccines have their own disadvantages. For example, compared with some next-generation platforms, they take longer to culture and produce. Protection from an inactivated vaccine is usually weaker, so large amounts of antigens are needed to achieve an adequate immune response. This means people may need several injections or “booster” doses. These shortfalls may be more relevant during a pandemic when large numbers of shots are needed quickly.