Philadelphia’s new mask mandates should help slow the spread of COVID-19, health experts said Wednesday, but what’s most needed to arrest rising case counts is a boost in vaccination rates.

“We need the city to do whatever it can to ensure vaccinations ... and at the same time be responsive to the changes in trends,” said Usama Bilal, an assistant professor in Drexel University’s department of epidemiology and biostatistics.

Philadelphia will require masks in all public areas of city buildings, at unseated outdoor gatherings of more than 1,000 people, and in indoor businesses and institutions, unless the business requires all staff and patrons to confirm they’re vaccinated. In restaurants and bars, staff must all be masked and diners must wear masks to their tables until they are served food or drinks, when they can remove them. The city has yet to implement any capacity limits, though.

Philadelphia also required all new city employees be vaccinated, and existing employees be vaccinated or wear two masks while working.

The delta variant spreads far more effectively than previous iterations of COVID-19, fueling surges around the country and eroding vaccine protection. Average new cases each day have doubled three times in the last month, said Cheryl Bettigole, the city’s acting health commissioner, in a news conference Wednesday.

Though “breakthrough” infections in the vaccinated have been reported, the vast majority of serious cases and deaths still occur in the unvaccinated. Citywide about 77% of people have received at least one vaccine dose, but that number masks significant variations in vaccination rates by neighborhood. In a few zip codes, less than 40% of people are vaccinated.

» READ MORE: In Philly’s least-vaccinated zip codes, fighting the delta variant is a game of catch-up

”Since we don’t have the vaccination rates we hoped we would have,” Bilal said, “we need to combine that with other measures.”

The effectiveness of the new restrictions is difficult to predict, experts said, and will depend on compliance, enforcement, and vaccination rates. Bilal said allowing restaurants to continue operating at full capacity would likely prove a liability, as indoor dining creates an opportunity for superspreader events. Another Drexel epidemiologist, Michael LeVasseur, wasn’t sure what the effect would be, saying it could depend on ventilation, how crowded the space is, and how effectively delta spreads indoors.

“People are producing more virus than we saw in the past,” he said. “I do not know what that means for the grocery store. I don’t know what that means for a restaurant.”

Another unknown: how people will react if the virus continues to ebb and surge, prompting restrictions to change in ways frustrating to a pandemic-weary public.

“People need to be patient with these things, the ebbs and flows,” Bilal said. “That’s going to happen with the virus and it’s going to happen with the restrictions, and that’s perfectly normal.”

There is hope among some public health experts, though, that the new requirements, along with fear of the delta variant, may nudge some into getting shots. Philadelphia’s unvaccinated are less likely than residents of more conservative communities to avoid shots over ideological or political reasons, health experts have said. Distrust of the health-care system, questions about the vaccines’ safety, misinformation fueled by social media, and not making vaccination a priority are more likely reasons for reticence.

“We’re talking to people who were still on that fence and delta was actually pushing them onto the vaccination side,” said Sarah Bauerle Bass, director of Temple University’s Risk Communication Laboratory. “I do think we’re going to see more of those folks who still had that hesitation.”

LeVasseur agreed, comparing restrictions that will keep unvaccinated people out of certain businesses to cigarette taxes that successfully encouraged smokers to kick the habit.

New masking mandates come just over two months after the city lifted earlier mask requirements, causing a feeling of whiplash for some who were enjoying normal activities.

”I think it’s going to be difficult for some people to get back into the swing of it,” said LeVasseur. “Those who were wearing masks before will wear masks again. Those who hated it are going to be more reluctant to do it and more angry about it.”

The new restrictions are warranted, though, he said. Since the beginning of August, Philadelphia has reported about 5% of all COVID-19 tests are positive, a red flag for wider community spread. He noted it was likely inevitable that the delta variant would circulate in the United States, though low vaccination rates are helping it flourish.

Wednesday, Bettigole said in about two-thirds of cases when the infected person could identify where they caught COVID-19, the transmission was traced to a family or friend in the home. But that doesn’t mean public spaces are especially safe, LeVasseur said, since your exposure source is obvious if someone you know tests positive, and impossible to identify if it’s a stranger in a bar.

And mask requirements are a critical protection for people who have to be at work.

”People working in a bar, people working in a supermarket, we need to be protecting workers,” Bilal said. “To protect those people is one of the key goals of the indoor mask mandate.”

There is some overlap, Bilal said, between people in low-wage jobs that require people to work in-person and people who live in some of the least vaccinated neighborhoods in the city, he said.

Masking restrictions can be especially tough in such communities, said Cornelius Pitts, director of the COVID-19 Vaccination Response Project for Temple University’s Lewis Katz School of Medicine. He has been working to increase vaccination rates in some of the city’s least inoculated neighborhoods.

» READ MORE: Delta has us masking again, but which masks work best?

“The people we are talking to are pretty much doing as they please,” Pitts said. “Some of them don’t even believe the virus is a thing. Some of them are not wearing masks. Even with the mandates they probably won’t adhere to them.”

People in those neighborhoods rely on corner stores and bodegas rather than big supermarkets, he said, and he questioned how stringent those businesses would be about requiring masks.

The restrictions, though, offer a consistent baseline citywide, he said. Some people will ignore them. Everyone won’t behave exactly in accordance with restrictions, but it is an intervention that will have an effect, he said.

Still, he and other health experts agreed that the new mandates are much likelier to protect people than doing nothing.

“What we need to do is intervene to minimize risk,” LeVasseur said. “If we are going to keep bars open, let’s do things to keep risks as low as possible.”