Pointing to a handful of new studies, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a recent briefing that after both doses, the mRNA vaccine from Pfizer-BioNTech is about 80 percent effective at preventing infection from the delta variant, 88 percent effective at preventing symptomatic disease and 96 percent effective at preventing hospitalization caused by delta. New data out of Israel, however, shows lower rates of effectiveness — around 64 percent protection from infection and 93 percent protection from serious illness and hospitalization. (Moderna’s vaccine also uses mRNA technology and has shown similar rates of overall effectiveness to the Pfizer-BioNTech in previous studies.)

The key to this protection, however, is full vaccination, Pekosz says. “If you’ve only gotten one of your mRNA shots, that’s where you can really see the delta variant being able to evade some of those immune responses,” he says. In fact, one dose of the two-dose mRNA vaccines was found to be only 33 percent effective at preventing symptomatic disease caused by the delta variant in a preprint study out of the U.K.

“So if you’ve got a good strong immune response generated by both doses of the mRNA vaccine, then you should be in a good place,” Pekosz says. “But if you’re only partially immune — if you’re in between doses or if you take in the first dose and you decide to skip the second dose — then you’re in an area where the vaccine may protect you against older strains, but it may not be enough immunity to protect you against the delta variant.”

Johnson & Johnson released a statement on July 1 noting that its one-shot vaccine “generated strong, persistent activity against the rapidly spreading delta variant and other highly prevalent SARS-CoV-2 viral variants.” The studies containing this data are currently being submitted for publication. Hours before J&J’s announcement, Fauci said it’s reasonable to assume the effectiveness of J&J’s vaccine is on par with AstraZeneca’s vaccine, which uses the same viral vector technology. The AstraZeneca vaccine, which isn’t authorized for use in the U.S., has been shown to be 60 percent effective at preventing infection and 92 percent effective at preventing hospitalization caused by the delta variant.

Experts will be keeping a close eye on the strength and duration of these vaccines — especially in more vulnerable populations. Pekosz doesn’t see the need for a national booster campaign yet but says it’s not outside the realm of possibilities that “highly vulnerable populations might be asked to go in and take a booster that consists of the delta variant or maybe the next variant that comes by, just to make sure that they’re maintaining that level of immunity.”

5. You may still want to keep your mask handy

Fully vaccinated individuals no longer need to wear a mask in most situations, according to CDC guidance issued in mid-May. But experts say you may want to keep one handy — especially with delta on the tear.

The reason? No vaccine is 100 percent effective at preventing infection or illness, and with a highly transmissible virus gaining traction in a number of communities throughout the country, a little extra caution makes sense, Pekosz says: “If you know you’re in a situation where you’ll be coming in contact with people who might be carrying the virus, it’s always best to have another layer of protection, like a mask or some level of social distancing.”

Los Angeles County recently recommended that its residents, regardless of vaccination status, wear masks in indoor public settings “until we better understand how and to who the delta variant is spreading.” The area has seen a surge in new COVID-19 cases, likely attributable to delta.

Timothy Brewer, M.D., a professor of medicine and epidemiology at the University of California, Los Angeles (UCLA), says there’s no good evidence to suggest that vaccinated individuals need to mask up when they’re outside, but it’s “probably reasonable to consider wearing a mask when you’re indoors and around lots of other people, particularly if you can’t physically distance.” He still wears a mask at the grocery store and says he would do the same if he were going to a large indoor event “like a concert or a movie theater.”

It’s unclear whether other communities will follow L.A. County and issue new mask guidelines. In the meantime, experts say, pay attention to what’s happening in your area. If vaccination rates are high where you are, there’s less of a risk. “The more you’re exposed to people who are unvaccinated, that possibility of getting infected increases,” El-Sadr says.

Keep this in mind, too, as you travel this summer — especially considering that more than one-third of U.S. counties have vaccination rates under 30 percent, according to CDC data.

“If the risk increases, why not do something to help mitigate that risk? Mask wearing is an easy” solution, Pekosz says.