Joseph G. Allen is an associate professor and director of the Healthy Buildings program at Harvard University’s T.H. Chan School of Public Health. He co-wrote “Healthy Buildings: How Indoor Spaces Drive Performance and Productivity.”

The World Health Organization recently said vaccinated people should wear a mask indoors. Los Angeles County went one step further and mandated masks for all. And the American Academy of Pediatrics said this week that all kids should be masked in school this fall, even those who are vaccinated.

People may be confused: Did the science change since the Centers for Disease Control and Prevention told vaccinated people that they don’t have to wear masks indoors? Is there some new data showing the vaccines don’t work?

No. Efforts to bring back masking for those vaccinated are misguided. All of the vaccines approved for use in the United States remain effective against all covid-19 variants, including delta.

The mRNA vaccines (Pfizer and Moderna) are still more than 90 percent effective at blocking infection, and even better at reducing the threat of severe disease and death. Meanwhile, two recent studies show that the Johnson & Johnson vaccine not only elicits a strong immune response against delta, but also that the neutralizing antibody response doesn’t wane over time. In fact, it improves.

What about “breakthrough” infections, the positive tests reported among vaccinated people? Fortunately, breakthroughs are rare, and the terminology is misleading.

Take the recent study of people in prisons that found 27 positive cases out of 2,380 vaccinated individuals. These “breakthroughs” amounted to 1.1 percent of participants and, more importantly, none were symptomatic. They were only discovered because of routine screening. Testing can be so sensitive that it detects even a handful of virus particles in the nose as the immune system wards them off.

It’s hard to see how these are “breakthroughs” in any meaningful way. Sure, the virus was detected and therefore the test was positive, but it’s clinically irrelevant. But when the public hears the word “breakthrough,” it sounds like the vaccines failed, when the opposite is true.

Potential breakthroughs is what has led some notable scientists to support indoor masking, even for vaccinated people. But if vaccinated people are asymptomatic, we know their viral load is lower, as a recent New England Journal of Medicine study found. This makes them less likely to transmit and a low threat to others.

A fair response might be that some breakthrough infections are symptomatic. That’s true, but with one major flaw: If a person is symptomatic, shouldn’t they be home? Anyone with symptomatic illness should stay away from others.

We also know this virus does not impact kids in the same way it impacts adults. Three major studies over the past year all found the risk of death to be in the range of 1 in 100,000 to 1 in 1 million. Hospitalization rates for school-aged kids younger than 12 (the group that can’t get vaccinated yet) hovered around 3 or 4 per million throughout the pandemic, reaching just under 1 per 100,000 at the worst point in January. Multisystem inflammatory syndrome, a serious condition that can affect children with covid-19, remains rare, and, thankfully, a recent study found inflammation and cardiac symptoms resolved rapidly.

There are also vast differences in risk by region due to uneven vaccination rates. This is why blanket statements about masks don’t make sense. Sure, in some areas experiencing an outbreak, such as Arkansas, reinstituting mask mandates might make sense. But what about Vermont, where cases, hospitalizations and deaths are very low? Is there no level low enough that the AAP would say kids can take off their masks? We need to start answering these questions, because there is a very real possibility that vaccines won’t be approved for kids under 12. What then? Masks indefinitely for kids? It’s an untenable position.

For those who say universal mask mandates are necessary because many unvaccinated people are not following the CDC’s “honor system,” I’d point them right back to the fact that the vaccines work. Yes, unvaccinated people who refuse to wear masks put themselves at risk, but not people who are vaccinated. And those who want to get vaccinated but are unable can wear N95 masks — the same used in hospitals pre-vaccine to great effect.

If wearing a mask even after being vaccinated makes a person more comfortable, I fully support them. But it is also perfectly reasonable for vaccinated people to not want to wear them. I am fully vaccinated and do not feel the need to mask indoors. I am not being cavalier with my health or anyone else’s. The vaccines protect me and others about as well as anything can in life. Delta has not changed this.

Nor can anyone dismiss me as an anti-masker. I wrote in support of masks as early April 2020 and consistently urged their use for more than a year since. But vaccines have changed the threat, and the CDC’s guidance from May remains the most accurate and relevant for the United States. It’s straightforward: If you’re vaccinated, you don’t need to wear a mask. If you’re not, you should.