New COVID-19 Vaccine Defends Monkeys Against Infection

River D'Almeida, Ph.D
2 min readMay 7, 2020

Researchers from Beijing-based Sinovac Biotech have reported preliminary results of a study into the development of a vaccine against COVID-19. This is some of the first evidence of a vaccine showing efficacy in a primate experimental model (rhesus macaques) and provides hope for a global community anxiously awaiting countermeasures against the escalating pandemic.

Experts estimate that a clinically-available vaccine against SARS-CoV-2 could take 18 months or longer to develop, even at an accelerated pandemic pace. A new vaccine needs to be thoroughly tested for safety and efficacy in animals and humans prior to its commercialization. Before phase I testing, in which a small group of healthy volunteers receives the vaccine in development, vaccines are typically tested in non-human primates, which share physiological and disease process similarities with humans.

In Sinovac’s study, the vaccine testing protocol involved two doses of inactivated SARS-CoV-2, administered to a cohort of eight rhesus monkeys. The animals were allowed to develop a natural immune response to the inactivated virus over the course of three weeks. They were then exposed to live, unadulterated SARS-CoV-2 to test the protective capabilities of the vaccine treatment.

Encouragingly, none of the monkeys experienced the symptoms of severe infection, nor had any unwanted side-effects as a result of the shot. Meanwhile, the control animals developed pneumonia and high levels of circulating virus as a result of exposure to the coronavirus.

In response to these findings, Florian Krammer, a virologist based at the Icahn School of Medicine at Mount Sinai said, “This is old school but it might work. What I like most is that many vaccine producers, also in lower-middle-income countries, could make such a vaccine.”

While promising, experts warn that preclinical validation of a new vaccine will involve much more work: larger testing cohorts to provide statistical significance and testing protection against viral strains that specifically infect humans and escape variant strains.

Sinovac has already launched phase I human trials of its vaccine in China to evaluate the safety and degree of protection in over 100 volunteers. If these clinical trials go as planned, phase II studies will kick off in mid-May in a larger group of over 1,000 individuals.

Originally published at on May 7, 2020.

River D'Almeida, Ph.D

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