Hopeful news, but still early days:

For the first time, one of the many COVID-19 vaccines in development has protected an animal, rhesus macaques, from infection by the new coronavirus, scientists report. The vaccine, an old-fashioned formulation consisting of a chemically inactivated version of the virus, produced no obvious side effects in the monkeys, and human trials began on 16 April.

Researchers from Sinovac Biotech, a privately held Beijing-based company, 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 tubes down their tracheas, and none developed a full-blown infection.

"I like it,” says Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai who has co-authored a status report about the many different COVID-19 vaccines in development. “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.

But Douglas Reed of the University of Pittsburgh, who is developing and testing COVID-19 vaccines in monkey studies, says the number of animals was too small to yield statistically significant results. His team also has a manuscript in preparation that raises concerns about the way the Sinovac team grew the stock of novel coronavirus used to challenge the animals: It may have caused changes that make it less reflective of the ones that infect humans.

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 given the virus “mimic COVID-19-like symptoms.”

(Thanks to Dr. David Ozonoff for the pointer.)