BOSTON — They will not be tested in humans, but six vaccine candidates against COVID-19, designed for lab-use only, have proven what has probably been assumed by many: that infections with the novel coronavirus can, conceptually, be prevented through immunization.
"Currently there's very little evidence in humans about whether natural immunity or vaccine-induced immunity can protect," said Dr. Dan Barouch, one of the researchers at Beth Israel Deaconess Medical Center. "So we addressed these two questions in an animal model, rhesus monkeys."
Although rhesus monkeys have 93% similarity in DNA with humans, they are by no means 'stand-ins' for people in pharmaceutical studies.
"This is an animal study. And therefore extrapolations for humans needs to be done very carefully and will require definitive, large-scale clinical trials for proof," Dr. Barouch said.
To gauge the development of natural immunity, nine rhesus monkeys were infected with COVID-19. The animals recovered. Some 30 days later, they were re-exposed to the virus without ill effect.
"These data suggest that there is indeed natural protective immunity to the virus," Dr. Barouch said.
As for the monkeys administered the six vaccines, there were 25 in all. Another 10 monkeys served as 'controls,' meaning they were injected with a non-active substance.
The vaccines were all derived from the anatomical 'spike' on the COVID-19 virus, which is the part responsible for invading cells.
Three weeks later, and after the vaccinated group received a booster shot, all 35 primates were exposed to COVID-19.
"Monkeys that were vaccinated with these vaccines developed neutralizing antibodies and were then protected against COVID-19 challenge," Dr. Barouch said. "Some animals were protected fully. In other words, no virus was detected in their lungs or their noses after exposure to the virus. And some were protected only partially, but they still had a lower level of virus than controls."
One drawback to the study was its small size, said Dr. Debra Poutsiaka, an infectious disease physician at Tufts Medical Center.
Dr. Poutsiaka, who is currently running trials testing the effectiveness of the anti-viral drug remdesivir against COVID-19, said it's one thing to induce an immune response and quite another to protect against disease. She said the Beth Israel data did not show the latter.
"And that's basically where the money is. I don't mean money like in an investment sense, I mean in a payoff for public health," she said.
Asked whether the findings might accelerate the development of a human vaccination, Dr. Poutsiaka could only say that at least it didn’t set things back.
“Look at it this way. If this study was completely negative, meaning there was no immune response noted or there was some harm the vaccine caused, that would have not been a step in the right direction,” she said.
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