After the highly transmissible delta variant of the coronavirus started to spread in Israel and infected some people who had been fully vaccinated, the country reintroduced a requirement for everyone to wear masks in public indoor settings two weeks after letting it expire. In Los Angeles County, where the delta variant is beginning to spread now, the public health department has recommended that people who are vaccinated should wear masks indoors in public. World Health Organization officials also recently recommended that people who are fully vaccinated should still wear masks. But the CDC still says that it isn’t necessary.
If you live in the U.S. and you’re vaccinated, you might have stopped wearing a mask inside in May, when the CDC said that masks were only necessary for people who hadn’t gotten the shots—or in a few specific situations, like riding on a plane or bus. But should that change now?
“What I would personally recommend is in places where case counts are rising, it makes sense for us to be more cautious, including the wearing of masks,” says David Dowdy, an associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health. Still, he says, delta variant cases won’t necessarily go up in the U.S. in the same way that they have in other countries. “We’ve seen a big surge in the U.K., for example, but we have not seen that same surge across Europe, in the U.S., and Canada. So it’s not inevitable that we’re all going to go the same way as the U.K.” At the same time, the prevalence of the delta variant in the U.S. has doubled in the last two weeks. In Los Angeles, where cases of delta are quickly rising (and total cases have started to rise slightly), it was reasonable to recommend the extra precaution of masks, he says. If local outbreaks arise elsewhere, we should be prepared to take some extra steps, including both wearing masks and social distancing.
The variant, which was first identified in India, appears to be as much as 60% more transmissible than the Alpha variant that emerged in the U.K. The alpha variant was itself 50% more transmissible than the original virus that emerged in China. Because it spreads so easily, masks can be helpful indoors, even though “the vaccines are actually holding up pretty well” against the variant, says Tim Brewer, an epidemiology professor at the epidemiology at the UCLA Fielding School of Public Health.
There may be differences between the vaccines; there’s evidence that both the Pfizer and Moderna vaccines work well, but it’s not yet clear how the Johnson & Johnson vaccine may fare. [UPDATE: Johnson & Johnson released data from two small studies saying that its vaccine is effective against the Delta variant, with only a small drop in potency.] Lab tests of the Moderna vaccine found only a “modest reduction” in antibodies that can fight the Delta variant. A preprint study from the U.K. suggests that if you’ve gotten two doses of the Pfizer-BioNTech or AstraZeneca vaccine, you’re nearly as well protected from getting sick from delta as from the original virus. But with only one dose, the effectiveness drops substantially, to around 33%. (In response, the U.K. delayed the next step of its reopening plan so that it could speed up second doses.) In the U.S., millions of people have missed their second doses. A single dose was also a little less effective at preventing severe disease that could cause someone to be hospitalized, though two doses are effective. In Israel, when some fully vaccinated people were recently infected with the Delta variant, most cases were mild or had no symptoms at all.
Since no current COVID vaccine is 100% effective, if there’s a surge in cases, it makes sense for even fully vaccinated people to be a little bit more cautious. “Wearing a mask, particularly in indoor settings, whether that’s stores or restaurants when you’re not eating, will help to interrupt transmission, and both protect people from getting sick and if they do get sick, protect others from having infection spread to them,” says Brewer.
But it’s even more important that people who aren’t vaccinated yet quickly get the vaccine before the delta variant reaches them. “We really need to figure out two things,” says Brewer. “One, we need to figure out how to convince people in countries like the United States who are hesitant, for whatever reason, to get vaccinated, and to try to address their concerns and help them understand why being vaccinated will both help them and the community. Secondly, we have to figure out how to get vaccines to all the other countries that don’t have vaccines.”
Some poorer countries may not have enough vaccines for their full populations until 2023. That means both that more people will become ill and die, and that the virus will continue to mutate. “That’s really worrisome,” he says. “The more we have transmission, the more it’s going to lead to the creation of new variants.”
Editor’s note: This story has been updated.