The Philadelphia region — except for Delaware County — was seeing high coronavirus transmission rates as of Tuesday, according to the CDC, and local health officials said they are continuing to watch rising hospitalizations, particularly among the unvaccinated.

Throughout the pandemic, rising case counts have precipitated an increase in hospitalizations. This summer, the spread of the highly transmissible delta variant has not deviated from the sobering trend, with most patients being unvaccinated.

In Philadelphia and South Jersey, coronavirus hospitalizations have tripled since last month, spokespeople for the city and Camden County said. In the western suburbs, Bryn Mawr, Paoli, and Riddle Hospitals and Lankenau Medical Center were treating more than 50 patients for virus-related complications as of Monday, up from zero patients on July 4, said Jonathan Stallkamp, interim chief medical officer for Main Line Health.

“We’re definitely not at the peak of this next wave,” said Stallkamp, a physician, adding that Main Line patients include seriously ill young people without preexisting conditions. “It’s sad to watch.”

As long as the vaccination rate doesn’t see a massive and sudden increase, and delta remains dominant, the virus appears primed to keep spreading across the region, erasing any early-summer hopes of the pandemic retreating, health officials warn.

Nationwide, new case counts are the highest they’ve been in six months, with hospitals overwhelmed in some states. In Pennsylvania, case counts have doubled over the last two weeks, according to the New York Times, with hospitalizations increasing, too, but at a slower rate. Both metrics are rising in New Jersey, too, though less rapidly.

Michael Levy, an associate professor of epidemiology at the University of Pennsylvania, said he looks at that “momentum” and worries that the number of infections will continue to rise, especially as students return to their classrooms and college campuses this fall.

“Don’t think it’s not going to happen here,” Levy said. “We saw delta go through India, go through Britain [where 61% of the population is fully vaccinated]. … I think we should be worried.”

“Places that have vaccination rates as high as Philly are getting hit,” he added. About half of the city’s total population, including children not yet eligible for shots, are fully vaccinated.

Most people getting sick — and the vast majority of those being hospitalized — have not had their shots, officials and physicians say, providing further evidence that vaccines are working.

Across the Philadelphia region, public health leaders said they hope enough people are vaccinated to prevent a repeat of the surge last winter, before the shots were widely available.

» READ MORE: Some people’s minds are changing about the coronavirus vaccine. Here’s how doctors persuade them.

“If we’ve learned anything from this pandemic, it’s to not expect anything,” Philadelphia spokesperson James Garrow said. “It’s our hope that our high vaccine rate, coupled with masking, will help flatten the curve of new cases, and keep our hospitals from being overwhelmed.”

In Bucks County, where 29 people were hospitalized with the virus as of Tuesday, officials said they were heartened to see that neither hospitalizations nor deaths have “increased in proportion” to the increase in cases.

“While we may see an increase as the weather turns colder, we do not anticipate anything on the scale of last winter,” county officials said, ”nor do we expect to see the level of hospitalizations and deaths that we encountered a year ago.”

Chester County’s vaccination rate, the region’s highest, should help it “weather” a surge, said county health director Jeanne Franklin.

“If a surge increases” — excluding the introduction of another variant — “we anticipate [the surge] to last for a shorter time,” Franklin said in a statement. “But really the crystal ball is still nowhere to be found!”

About 54% of Pennsylvanians, including children under 12 who aren’t yet eligible for shots, are fully vaccinated, according to the New York Times, as are 60% of New Jerseyans. In Philadelphia and its collar counties, the rate ranges from about 50% in the city to 63% in Chester County, according to state and city data.

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Even more people have received one dose of a two-dose vaccine, and the number of first doses has recently ticked up in some places. But experts say both shots are needed for the most protection.

Health experts say this is especially important in the face of the delta variant, which is more transmissible than earlier forms of the virus, and it sometimes spreads through vaccinated people, even if they don’t feel sick, and can occasionally make the immunized mildly ill.

Its rise has led to a bevy of new mitigation measures: Days after Philadelphia brought back its indoor mask mandate, Montgomery County on Monday formally recommended that people mask up indoors. The move echoed the Centers for Disease and Control and Prevention’s universal masking recommendation for any counties experiencing high or substantial spread, which was announced last month.

“Because of the delta variant, Montgomery County has seen increases in our key COVID-19 indicators for the past several weeks. However, I want to be very clear that the vast majority of the new cases are occurring in unvaccinated individuals,” Montgomery County Commissioner Chair Val Arkoosh said Monday at a briefing. “The quickest way to get this pandemic under control is to get vaccinated.”

» READ MORE: Pa., N.J., and Del. leaders weigh vaccine-verification options, but largely hold off on mandates

As it sees a growing proportion of cases in children and teenagers, Camden County is focusing on increasing vaccinations among those age groups before the school year starts.

“Vaccinations and social behavior will dictate what this winter looks like,” said county spokesperson Dan Keashen. “It will be incumbent upon us to do everything we can to avoid another surge like we had last winter.”

Levy, the Penn epidemiologist, said any increase in vaccinations would be “hugely important,” and he’d like to see an even greater, on-the-ground push at this critical juncture.

While it’s unclear whether vaccines can stop the spread of delta, “vaccines slow the spread,” he said. “And that means everything because this thing is just [about] momentum. Everything we can do to slow it down is going to lead to fewer people getting infected before they get protected. "