Coronavirus

Should you wear a mask indoors if you’re vaccinated? Dr. Ashish Jha says it depends.

“It depends largely on where you live ... and your risk tolerance.”

Dr. Ashish Jha is one of the most quoted experts in his field. He was doing 40 media requests a day in the spring, but has since scaled back to 15 to 20 a day. Now, he is weighing in on mask mandates indoors. Jonathan Wiggs/Globe Staff

As a sense of pre-pandemic normalcy returns and the new Delta variant emerges, should vaccinated people be wearing masks indoors?

Dr. Ashish Jha, professor and dean at Brown’s School of Public Health, weighed in on this question on Wednesday in a Boston Globe op-ed. His answer – it depends.

“It’s confusing,” Jha said. “So who’s right and how are Americans to navigate this?”

In the op-ed and in a tweet, Jha referenced how the World Health Organization (WHO) and the Los Angeles Health department says everyone should wear masks indoors, while the Center of Disease Control and Prevention (CDC) says those who are vaccinated should not have to. 

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“Well, it turns out, it’s nuanced,” Jha wrote in the tweet. “It depends largely on where you live … and your risk tolerance.”

In Massachusetts, the mask mandate for indoor spaces – excluding public transportation, healthcare facilities, and any vulnerable population settings – was lifted on May 29. The Department of Health still requires unvaccinated people to continue wearing their masks.

Jha explained the two sides by discussing the logic behind both and how they play out in different populations. 

“If you are fully vaccinated and encounter the Delta variant, you are about 90 percent less likely to be infected than if you had not been vaccinated,” Jha wrote. “And if you do get infected, you are extremely unlikely to get very sick.”

Despite the vaccine’s effectiveness, Jha said the risk is much higher in areas where many people are still unvaccinated. 

“If a vaccinated person encounters the virus repeatedly or in high enough concentrations, the chances of a breakthrough infection gets more substantial,” Jha wrote.

Vaccines, Variants & Masks:

Massachusetts has more than double the fully vaccinated population of the total people eligible in Mississippi. Jha compared the vaccine to the star goalie of a hockey team – Gerry Cheevers in his example – who blocks the virus instead of pucks.

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“In Massachusetts, there isn’t much virus around to even put a shot on target, and therefore little reason to wear a mask indoors,” Jha wrote. “In Mississippi, there are simply many more shots on goal, and even a terrific goalie will occasionally let a shot in.”

Jha also said since there is no system of checking who is vaccinated, many unvaccinated people do not wear masks indoors, despite being advised to.

“Indoor masking can’t be enforced on unvaccinated people only without [a] vaccine verification system,” Jha tweeted.

As for himself, Jha says while living in New England – a highly vaccinated area – he wears masks intermittently depending on the crowd size.

“If I were in SW Missouri and many other places with low vax, high cases, I’d wear a mask indoor reliably,” Jha tweeted. “Your preferences may differ.”

Jha ultimately concludes there is not one correct answer because so much varies by state and by community. 

“As we wind our way through this pandemic, we are now entering a phase where guidance will — and should — be local and will change as the realities on the ground change,” Jha wrote.

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