New research suggests vaccines reduce risk of COVID-19 spread through nose and mouth

People who are vaccinated against COVID-19 not only protect themselves, but are also likely reducing the risk of spreading the disease and infecting others, according to new Army research.

Vaccine research at the emerging infectious diseases branch of the Walter Reed Army Institute of Research monitored the amount of virus that replicates in the noses, sinuses and throats of monkeys after they are vaccinated. Monkeys, like humans, can still become infected with COVID-19 after they are vaccinated, but the vaccine reduces the severity of the illness.

The research found that for monkeys that were vaccinated and then infected, “there’s a rapid decline in the amount of virus that’s reproducing” in their noses and upper airways, said Dr. Kayvon Modjarrad, director of infectious disease research at Walter Reed.

“That’s where the transmission occurs, and the disease occurs down in the lungs. But if you have lots of replicating virus up in your nose, sinuses, pharynx, that’s where you’re going to transmit,” Modjarrad said in an interview with McClatchy.

The lab measured the amount of virus in the noses and upper airways of monkeys during the trials of its own coronavirus vaccine. Modjarrad said the reduction in the amount of virus in the animals was a way to measure the vaccine’s effectiveness

The research also found what other vaccine clinical trials have shown, that vaccination can reduce the risk of transmission.

“We saw that in the animal studies. So we expected that there would be probably some reduction in transmission in humans. And now we’re starting to see that in these real-world studies,” Modjarrad said.


Other data has emerged suggesting the available COVID-19 vaccines — produced by Pfizer, Moderna, and Johnson & Johnson — lower the risk of vaccinated individuals spreading the virus to others.

A recent study published by the University of Cambridge and Public Health England found a statistically significant decrease in infection risk to others from individuals who were vaccinated. Another study focused on the Pfizer vaccine and conducted in Israel, published in The New England Journal of Medicine, found similar results.

The Centers for Disease Control and Prevention released preliminary guidance for vaccinated individuals last week. The agency said it is safe for vaccinated people to congregate indoors unmasked with other vaccinated people, or to meet indoors with unvaccinated people from one other household if they are at low risk of contracting severe COVID-19.

But the agency is still encouraging vaccinated people to wear masks and social distance in public, to avoid carrying the virus and infecting others.

Paul Offit, a member of the Food and Drug Administration’s vaccine advisory board and director of the vaccine education center at the Children’s Hospital of Philadelphia, said that vaccinated people should continue taking precautions for other reasons.

“I’m fully vaccinated, and I wear a mask and social distance for selfish reasons,” he said. “I may be one of those one in twenty people who isn’t protected. I mean, it’s 95% effective.”

“It really all depends on the degree to which there is illness in the community,” Offit said. “When you get to the point where there are far fewer cases, and far fewer deaths, and you know there is much less virus in the community, then you can feel better if you’re vaccinated.”

The CDC has said it will continue to update its guidance on safe practices for vaccinated people as more scientific evidence emerges, and as more people get the shots.

“As more people get vaccinated and the science and evidence expands, and as the disease dynamics of this country change, we will continue to update this guidance,” Dr. Rochelle Walensky, the CDC director, told reporters.