December 7, 2023

Given that 50 million Americans are vaccinated against the coronavirus and millions more are being added every day, the urgent question on many minds is: When can I throw my mask away?

It’s a deeper question than it seems – about a return to normal, how quickly vaccinated Americans can hug loved ones, hang out with friends, and go to concerts, shopping malls, and restaurants without feeling threatened by the coronavirus.

Many civil servants are sure to be ready. On Tuesday, Texas lifted its mask mandate along with all corporate restrictions, and Mississippi quickly followed suit. The governors of both states cited falling infection rates and increasing numbers of citizens being vaccinated.

But the pandemic is not over yet and scientists advise patience.

It seems clear that small groups of people who have been vaccinated can get together without having to worry too much about infecting one another. The Centers for Disease Control and Prevention is expected to issue new guidelines shortly that will address small gatherings of vaccinated Americans.

But when vaccinated people can take off their masks in public places depends on how fast the disease rates drop and what percentage of people in the surrounding community remain unvaccinated.

Why? Scientists don’t know if people who are vaccinated will pass the virus to those who aren’t vaccinated. While all Covid-19 vaccines spectacularly protect people from serious illness and death, it is unclear how well they do in preventing the virus from taking root in one immunized person’s nose and then spreading to others.

It’s not uncommon for a vaccine to prevent serious illness but not infection. Vaccinations against flu, rotavirus, polio and pertussis are imperfect in this way.

The coronavirus vaccines “are being studied much more closely than any previous vaccine,” said Neeltje van Doremalen, an expert in preclinical vaccine development at the Rocky Mountain Laboratories of the National Institutes of Health in Montana.

And now coronavirus variants that evade the immune system are changing tartar. Some vaccines are less effective at preventing infections with certain variants and could theoretically allow more viruses to spread.

The research available so far on how well the vaccines prevent transmission is preliminary but promising. “We are confident there is a reduction,” said Natalie Dean, biostatistician at the University of Florida. “We don’t know the exact size, but it’s not 100 percent.”

Even an 80 percent decrease in communicability could be enough for vaccinated people to throw off their masks, experts say – especially when much of the population is vaccinated and the incidence of hospital stays and deaths drops.

But most Americans are still not vaccinated and more than 1,500 people die every day. Given the uncertainty surrounding transmission, even people who are vaccinated must continue to protect others by wearing masks, experts say.

“You should wear masks until we actually have evidence that vaccines prevent transmission,” said Dr. Anthony S. Fauci, Director of the National Institute for Allergies and Infectious Diseases.


March 3, 2021, 7:47 p.m. ET

This evidence is not yet in, as the vaccine clinical trials aimed to test whether the vaccines prevent serious illness and death, which usually reflects the effects of the virus on the lungs. Transmission, on the other hand, is driven by growth in the nose and throat.

Prepared by the vaccine, the body’s immune fighters should contain the virus shortly after infection, shorten the duration of the infection and reduce the amounts in the nose and throat. This should greatly reduce the chance that one vaccinated person will infect others.

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

Similarly, data from a few dozen Moderna study participants who were tested when they received their second dose suggested that the first dose reduced cases of infection by about two-thirds.

Another small batch of data recently emerged from the Johnson & Johnson study. The researchers looked for signs of infection in 3,000 participants for up to 71 days after receiving the single-dose vaccine. The risk of infection in this study appeared to decrease by about 74 percent.

“I think that’s very powerful,” said Dan Barouch, a virologist at Beth Israel Medical Center in Boston who ran one of the trial sites. “Those figure estimates could change with more data, but the effect seems to be pretty strong.”

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

However, clinical trials can overestimate the effectiveness of a vaccine because the type of people who choose to participate is already cautious and advised on precautionary measures during the trial.

Some researchers instead track infections among vaccinated people in real-world settings. For example, one study in Scotland performed tests every two weeks regardless of symptoms on health care workers who had received the Pfizer BioNTech vaccine. The researchers found that the vaccine’s effectiveness in preventing infection was 70 percent after one dose and 85 percent after the second.

Researchers in Israel examined infections in nearly 600,000 vaccinated people and tried to track down their household contacts. The scientists found a 46 percent decrease in infections after the first dose and 92 percent after the second. (The study may have missed infections in people with no symptoms.)

However, to get a real estimate of transmission, researchers really need to know which immunized people will be infected and then track the spread of the virus among their contacts using genetic analysis.

“This is the ideal way to actually do this,” said Dr. Larry Corey, a vaccine development expert at the Fred Hutchinson Cancer Research Center in Seattle. He hopes to conduct such a study in college-age students.

But what precautions should vaccinated people take pending the results of such studies? Currently, many experts believe that what is permissible depends 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 need to be to stop the spread.

“If the case numbers are zero, it doesn’t matter if it’s 70 percent or 100 percent,” said Zoe McLaren, a health policy expert at the University of Maryland, Baltimore County, on the vaccine’s effectiveness.

Wearing masks also depends on how many unvaccinated people remain in the population. Americans may need to remain cautious while vaccination rates are low. But people will be able to relax a bit when these rates rise and return to normal once the virus runs out of danger of infection.

“A lot of people think that masks are the first thing they do without,” said Dr. McLaren. In fact, she said, masks offer more freedom by allowing people to attend concerts, travel on buses or airplanes, or even go shopping with unvaccinated people nearby.

Ultimately, masks are a form of civic responsibility, said Sabra Klein, an immunologist at the Johns Hopkins Bloomberg School of Public Health.

“Do you wear a mask to protect yourself from severe Covid or do you wear a public health mask?” Said Dr. Small. “It is right to do your part in the community beyond yourself.”