rhesus macaque monkeys
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A prototype vaccine has protected monkeys from the coronavirus, researchers reported Wednesday, a finding that offers new hope for effective human vaccines.

Scientists are already testing coronavirus vaccines in people, but the initial trials are designed to determine safety, not how well a vaccine works. The research published Wednesday offers insight into what a vaccine must do to be effective and how to measure that.

"To me, this is convincing that a vaccine is possible," said Dr. Nelson Michael, director of the Center for Infectious Diseases Research at Walter Reed Army Institute of Research.

Dr. Dan Barouch, a virologist at Beth Israel Deaconess Medical Center in Boston, and his colleagues have started a series of experiments on monkeys to get a broader look at how coronaviruses affect monkeys - and whether vaccines might fight the pathogens. Their report was published in Science.

The scientists started by studying whether the monkeys become immune to the virus after getting sick. The team infected nine unvaccinated rhesus macaques with the new coronavirus.

The monkeys developed symptoms that resembled a moderate case of COVID-19, including inflammation in their lungs that led to pneumonia. The monkeys recovered after a few days, and Barouch and his colleagues found that the animals had begun making antibodies to the coronavirus.

Some of them turned out to be so-called neutralizing antibodies, meaning that they stopped the virus from entering cells and reproducing.

Thirty-five days after inoculating the monkeys, the researchers carried out a "re-challenge," spraying a second dose of the coronavirus into the noses of the animals.

The monkeys produced a surge of protective neutralizing antibodies. The coronavirus briefly managed to establish a small infection in the monkeys' noses but was soon wiped out.

These results don't necessarily mean that humans also develop strong, long-lasting immunity to the coronavirus.

In a separate experiment, Barouch and his colleagues tested prototype vaccines on rhesus macaques. Each monkey received pieces of DNA, which their cells turned into viral proteins designed to train the immune system to recognize the virus.

Some of the vaccines provided only partial protection. The one that worked best trained the immune system to recognize and attack the entire spike protein of the coronavirus. In eight monkeys, the researchers couldn't detect the virus at all.