Just as people are happily resuming life without face masks, alarms are sounding over the Delta variant, a highly contagious form of the coronavirus raging across the globe.
The World Health Organization last week urged even vaccinated people to wear masks indoors, and Los Angeles County health officials on Monday followed suit.
But health experts in Massachusetts and elsewhere are adamant that the Delta variant should not ruin our Fourth of July or require vaccinated people to dig out that box of paper masks. If you’re fully immunized, they say, you’re safe.
“There is no scientific reason why a vaccinated person should wear a mask anywhere, except for their own comfort,” said Dr. Shira I. Doron, hospital epidemiologist at Tufts Medical Center.
“This is the time to live. Enjoy yourself,” Doron added. “Right now, we’re in a really good place, here in Massachusetts.”
The Delta variant accounts for just over a quarter of coronavirus cases nationwide. But in Massachusetts, which has a much higher vaccination rate than most of the country, it was detected in just 5 percent of cases from May 23 to June 5.
Delta is expected to be the dominant strain nationwide by August, if not sooner, because it is so easily transmissible, said Dr. Ashish K. Jha, dean of the Brown University School of Public Health.
“The Delta variant is much more contagious than any variant we have seen so far,” he said Tuesday evening at a virtual forum sponsored by the City of Somerville.
Both the Moderna and Pfizer vaccines have been shown to work against the Delta variant, and the same result is expected for the Johnson & Johnson vaccine.
“All of our vaccines, particularly the Moderna and Pfizer vaccines, are doing very well among all variants,” Jha said.
The WHO’s advice addresses a world in which less than 15 percent of the population is vaccinated, some with less effective vaccines than those used in the United States, at a time when infection rates remain high in many regions.
In the United States, by contrast, COVID-19 cases are dropping and nearly half the population has been fully vaccinated.
That’s why the Centers for Disease Control and Prevention is not altering its advice that vaccinated people can ditch their masks in most situations. “If you are vaccinated, you are safe from the variants that are circulating here in the United States,” CDC director Rochelle Walensky said Wednesday on NBC News’ “Today.”
People are especially safe in Massachusetts, where 80 percent of adults have received a first dose, and 61.5 percent of all residents are fully vaccinated.
While the vaccines are highly effective, no vaccine is perfect and so-called breakthrough infections of inoculated people do occur on rare occasions.
Delta is “slightly more capable of causing breakthrough infections in vaccinated people, especially those who have yet to receive both shots, although such infections are much less likely to be serious and require hospitalization,” William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, said in an e-mail. “In unvaccinated people however, Delta seems more likely to cause severe disease requiring hospital treatment.”
In calculating your risk of becoming a breakthrough case, consider where you are, advised Jha, the Brown dean. Despite the overall decline, infections are increasing in states with low vaccination rates.
“If you’re a fully vaccinated person and walk into a room of all unvaccinated people, in a community where infection numbers are very high, it’s probably better to wear a mask,” he said. “If I was down in Mississippi or Texas [where vaccination rates are low] and walked into a crowded room, I would probably put on a mask.”
Massachusetts rescinded its mask requirements on May 29 and issued a new advisory mandating face coverings only in certain locations. “That advisory remains in place,” said a statement Wednesday from the state Department of Public Health.
Based on CDC guidance, Massachusetts requires masks in settings such as rideshares, taxis, public transit, health care and congregate care facilities, and shelters and prisons.
“It’s not because the CDC thinks vaccinated people aren’t safe” in those places, said Doron, the Tufts epidemiologist. Rather, it’s because people don’t have a choice about being in such settings, often cannot distance from others, and have no way of knowing who is unvaccinated, she said.
Requiring everyone to wear a mask in those settings provides comfort to those who can’t be vaccinated or who can’t mount an immune response to the vaccine, she said. “They don’t want to have to wonder if a person interacting closely with them is vaccinated.”
But doctors advise that immunocompromised patients continue to wear masks because they may not get full protection from the vaccine, Doron said.
The state advises all unvaccinated people to wear masks indoors and when they can’t socially distance. That would include children younger than 12, for whom a vaccine has not been approved. However, children younger than 5 are exempt from the requirement to masks in certain settings.
As for child care centers, there is no state requirement for workers to wear masks, and the Department of Early Education and Care “is not making any changes related to the Delta variant at this time,” said spokeswoman Martha A. Waldron.
Asked whether parents should request that child care providers wear masks, Doron recommended against it, at least not in Massachusetts. “There are some real downsides to doing that,” affecting children’s social and language development, she said.
The main takeaway from Delta’s emergence, Doron said, is “a big warning siren: Get everybody vaccinated.”
The health department’s statement likewise urged: “The best way to protect yourself, your loved ones and your community from COVID-19 and the variants is to get vaccinated. There are over 900 locations across the Commonwealth to get vaccinated in addition to in-home and mobile options. Visit vaxfinder.mass.gov for a list of vaccination locations.”
This story has been updated to clarify a statement by Dr. Shira Doron about the risk of the Delta variant for immunocompromised people.