DON’T HOLD YOUR BREATH

Plan to ditch the mask after vaccination? Not so fast

With people around the world immunised against the coronavirus, and millions more joining the ranks every day, the urgent question on many minds is: When can I throw away my mask?

It’s a deeper question than it seems — about a return to normalcy, about how soon vaccinated people can hug loved ones, get together with friends, and go to concerts, shopping malls and restaurants without feeling threatened by the coronavirus.

Certainly many US state officials are ready. Recently, Texas lifted its mask mandate, along with all restrictions on businesses, and Mississippi quickly followed suit. Governors in both states cited declining infection rates and rising numbers of citizens getting vaccinated.

But the pandemic is not yet over, and scientists are counselling patience.

It seems clear that small groups of vaccinated people can get together without much worry about infecting one another. But when vaccinated people can ditch the masks in public spaces will depend on how quickly the rates of disease drop and what percentage of people remain unvaccinated in the surrounding community.

Why? Scientists do not know whether vaccinated people spread the virus to those who are unvaccinated. While all of the Covid-19 vaccines are spectacularly good at shielding people from severe illness and death, the research is unclear on exactly how well they stop the virus from taking root in an immunised person’s nose and then spreading to others.

It’s not uncommon for a vaccine to forestall severe disease butnot infection. Inoculations against the flu, rotavirus, polio and pertussis are all imperfect in this way.

The coronavirus vaccines “are under alot more scrutiny than any of the previous vaccines ever have been”, said Neeltje van Doremalen, an expert in preclinical vaccine developmentat the National Institutes of Health’s Rocky Mountain Laboratories in Montana.

And now coronavirus variants that dodge the immune system are changing the calculus. Some vaccines are less effective at preventing infections with certain variants, and in theory could allow more virus to spread.

The research available so far on how well the vaccines prevent transmission is preliminary but promising.

“We feel confident that there’s a reduction,” said Natalie Dean, a bio statistician at the University of Florida. “We don’t know the exact magnitude, but it’s not 100%.

Still, even an 80% drop in transmiss - bility might be enough for immunised people to toss their masks, experts said — especially oncea majority of the population is inoculated, and as rates of cases, hospitalisations and deaths plummet.

But most Americans arestill unva cinated, and more than1,500 people are dying every day. So given the uncertainty around transmission, evenpeople who are immunised must continue to protect others by wearing masks, experts said.

“They should wear masks until we actually prove that vaccines prevent transmission,” said Dr Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases.

That proof is not yet in hand because the clinical trials for vaccines were designed to test whether the vaccines prevent serious illness and death, which usually reflects the virus’ effect on the lungs. Transmission, on the other hand, is driven by its growth in the nose and throat.

Primed by the vaccine, the body’s immune fighters should curb the virus soon after infection, shortening the infection period and curtailing the amounts in the nose and throat. That ought to significantly reduce the chances that a vaccinated person might infect others.

Animal studies support the theory. In one study, when monkeys were immunised and then exposed to the virus, seven of eight animals had no detectable virus in their noses or lung fluid, noted Juliet Morrison, a virus expert at the University of California, Riverside.

Similarly, data from a few dozen participants in the Moderna trial who were tested when they got their second doses suggested that the first dose had decreased cases of infection by about two-thirds.

Another small batch of data emerged recently from the Johnson & Johnson trial. Researchers looked for signs of infection in 3,000 participants up to 71 days after getting the-single-dose vaccine. Risk of infection in that study seemed to fall by about 74%.

“I think that’s very powerful,” said Dan Barouch, virus expert at Beth Israel Medical Center in Boston, who led oneof the trial sites. “Those number estimates could change with more data, but the effect seems quite strong.”

More data is expected in the coming months from both Pfizer-BioNTech and Moderna.

But clinical trials may overestimate the power of a vaccine, because the type of people who choose to participate already tend to be careful and are counselled on precautions during the trial.

Some researchers instead are tracking infections among immunised people in real-world settings. For example, a study in Scotland conducted tests every two weeks, regardless of symptoms, on healthcare workers who had received the Pfizer-BioNTechvaccine. Investigators found that the vaccine’s effectiveness in preventing infection was 70% after one dose, and 85% after the second.

Researchers in Israel assessed infections in almost 600,000 immunised people and tried to trace their household contacts. The scientists found a 46% drop in infections after the first dose and a 92% drop after the second. (The study may have missed infections in people without symptoms.)

But to get a true assessment of transmission, researchers really need to know which immunised people become infected, and then trace the spread of the virus among their contacts with genetic analysis.

“That’s the ideal way to actually do this,” said Dr Larry Corey, an expert in vaccine development atThe Fred Hutchinson Cancer Research Center in Seattle. He is hoping to conduct such a study in college-age students.

But what precautions should immunised people take until the results from such studies become available? At the moment, many experts believe that what’s permissible will depend to a large extent on the number of cases in the surrounding community.

The higher the number of cases, the greater the likelihood of transmission — and the more effective vaccines must be in order to stop the spread.

“If the case numbers are zero, it doesn’t matter whether it’s 70% or 100%,” said Zoe McLaren, a health policy expert at the University of Maryland, referring to vaccine effectiveness. © 2021

People should wear ntil we actually rove that vaccines revent transmission