Delta has us masking again, but which masks work best?

The COVID-19 delta variant, which experts say spreads more easily and might be more severe than earlier strains of the virus, has prompted new indoor mask recommendations. But are the masks that got people through a year and a half of pandemic going to do the job against delta?

Maybe not.

“With a virus that is now more easily transmitted you certainly are at increased risk than where you were a year ago,” said Joseph Teel, associate professor of clinical family medicine and community health at the University of Pennsylvania’s Perelman School of Medicine.

It is unclear why delta is more contagious, experts have said, with possibilities including people infected with the variant producing more viral particles or the virus being more effective at infecting cells. It’s possible, though, that whatever makes it more transmissible also would make some masks less effective. Thersa Sweet, associate professor in Drexel University’s department of epidemiology and biostatistics, suggested it could take fewer delta variant viral particles to infect a person, making masks that were good enough with prior strains of COVID-19 now unable to keep out the critical mass of delta particles.

“Wearing a mask, fewer viral particles get through, but since it takes less to cause an infection and make you ill, your mask might not be as protective for you now as it was six months ago,” Sweet said.

The Centers for Disease Control and Prevention last week issued a new indoor masking recommendation for Americans amid rising case counts, hospitalizations, and deaths due largely to the delta variant, and evidence that vaccinated people with breakthrough cases are able to transmit the virus.

The CDC did not respond to questions about whether it recommended certain types of masks. The Philadelphia Department of Public Health, which has recommended but not mandated indoor mask-wearing, emphasized wearing a mask at all was most important. It recommended that unvaccinated people consider double-masking.

“We just want folks to mask up,” said department spokesperson James Garrow. “In general, the more layers or more protection a mask affords the greater the level of protection.”

Even while recommending vaccinated people consider upgrading their masks, experts emphasized that vaccination remains the best possible protection against delta, or any other COVID-19 variant.

» READ MORE: Delta variant’s outdoor transmission is still unclear. Here’s how Philly experts are thinking about COVID-19 risk.

“We certainly know that the vaccine is highly effective at preventing serious infection, hospitalization, and death,” Sweet said.

But that risk of fully vaccinated people spreading the virus changes the equation in that population, roughly half the country, according to the Johns Hopkins Coronavirus Resource Center. A vaccinated person is likely to not contract COVID-19 if exposed to it, even the delta variant, but breakthrough cases, while rare, are less uncommon than once thought, and the extremely low risk of serious illness for the vaccinated doesn’t protect their contacts. Sweet emphasized vaccinated people who are infected can pose a risk to people who are immunocompromised or unvaccinated, particularly children under 12, who aren’t eligible for doses. They also can become yet another contributor to the development of other variants, including perhaps ones worse than delta.

“The less infections on a population level we have we’re going to be better off,” she said.

Masks can contribute to that goal, but it’s important to consider how efficient your mask is, and the seal it forms around your face. N95 masks, which are tested for efficiency by the National Institute for Occupational Safety and Health, are best bets, experts said.

“Personally, I recommend going to something that’s been tested to a standard,” said Anne Miller, executive director of Project N95, a nonprofit devoted to helping health-care personnel find reliable PPE since early in the pandemic.

The N95, with straps that go around the head and improve the mask’s seal, retail at big box hardware stores like Home Depot for about $1.68 a mask, and KN95s, a Chinese version of the N95 with ear loops instead of head straps, can be as cheap as 69 cents a mask, Miller said. However, the CDC warns that some KN95 masks are counterfeit.

The economics of masks concerned Teel.

“We always worry about health inequity and health disparity,” he said, “and does cost play into further health disparities?”

Surgical masks are cheaper and can be effective if used carefully -- no frequent pulling them up and down, for instance -- and cloth masks can be useful too, if they have multiple layers, or are doubled up. Sweet buys her masks on Etsy, she said, and looks for those with three layers, including one layer of silk or satin and one of cotton.

The length of potential exposure matters too, though. A quick trip to the store might not require as much protection as plans to linger indoors.

» READ MORE: These are the Philadelphia restaurants that require proof of vaccination

“If you’re going to be sitting in a small enclosed space for long periods of time, you’re going to want a better mask that has a really good fit,” Sweet said. “If you’re outside or you’re just popping in a store and out, you might not need as heavy-duty a mask. But that also goes to what your personal risk is, and how risky you’re willing to be.”

That question of personal risk is central to masking decisions. Do underlying health conditions, such as diabetes or other autoimmune issues, raise susceptibility to infection even if vaccinated? Are there young children or seniors at home? Will gatherings be crowded with people whose vaccine status isn’t certain?

“All of these decisions are very individual based on someone’s individual health circumstances,” Teel said. “Your own risk tolerance plays into it.”