Philadelphia’s COVID-19 case counts have steadily risen since the end of the city’s indoor mask mandate, but hospitalizations and deaths have not followed suit, a striking change to a pandemic-long pattern of infections leading to serious illness.

Just over two weeks ago, city Health Commissioner Cheryl Bettigole explained she was ending a new mandate after just four days in response to low hospitalization rates. The data since then have shown hospitalization rates have not gone up in lockstep with cases, not just in Philadelphia but nationally.

“If you think about it compared to two years ago when the original COVID strains came, it was a completely naive population,” said John Zurlo, chief of Jefferson Health’s infectious diseases division, referring to the fact that nobody had ever encountered this virus.

“Now we have considerable degrees of immunity from whatever strain,” he said. “I think what we’re seeing right now is perhaps as a consequence of that.”

Since 2020, a rise in cases has always been followed by increased hospitalization rates about two weeks later, then by heightened death rates.

That pattern led to the city’s tiered alert system introduced in February. When cases began rising again in April, the system triggered the return of the indoor mask mandate. Then, just four days after it began, the mandate ended. The number of people hospitalized with COVID declined for two days, and Bettigole called a halt to the mandate.

“We feel that decision was correct at the time and still believe that’s the case,” said Matthew Rankin, a spokesperson for the Philadelphia Department of Public Health, on Tuesday.

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Cases have been going up in the city since the beginning of April, but after an initial increase in hospitalizations of people with COVID, the count peaked at 82 on April 17, then plateaued, fluctuating from as high as 79 on April 27 to a low of 55 just two days later. The most recent data reported 78 people hospitalized with COVID in the city as of May 4. What’s more, the reported case counts are widely thought to be far lower than reality, because so many people are using home tests.

COVID data trackers don’t distinguish those who are hospitalized because of COVID and those who test positive but are admitted for other reasons. So even the hospitalization numbers may only reflect the prevalence of COVID in the region, and not that the virus itself is making people seriously ill.

“I really wish that data was teased apart so we know who is in the hospital because they are sick with COVID,” said Thersa Sweet, associate professor in Drexel University’s department of epidemiology and biostatistics.

Zurlo said one telling sign is that Jefferson’s intensive care units are not filled with people battling COVID.

Deaths from COVID have remained at their lowest point during the pandemic, ranging between a seven-day average of less than one to two a day since the beginning of April. An increase in deaths has always lagged case increases by several weeks, but health experts expressed cautious optimism that if the latest variant were going to prove more deadly, they would have seen signs by now.

“I think that’s the general feeling so far,” said Jennifer Kolker, associate dean for public health practice at Drexel University, “a hold-your-breath sort of feeling.”

Regional COVID death rates have followed a similar path, with death rates in South Jersey and the Philadelphia suburbs staying in the same low range as case counts surged. Hospitalizations regionally have increased since mid-April, but nowhere near as fast as cases. Since the beginning of April, case rates in Philadelphia have increased 145%, and 252% in nearby Pennsylvania counties. In that same time, hospitalizations across the area increased 83%.

Ashish Jha, the White House’s COVID-19 response coordinator, tweeted earlier this week that throughout the Northeast, deaths and hospitalizations have shown increases over the last six weeks but did not rise nearly as much as during past surges. He attributed that to the availability of booster shots, treatments, and testing.

“We’re at a point in the pandemic where we know how to manage the virus to keep infections low, to prevent serious illness, and to protect the most vulnerable,” Jha tweeted, “and that’s our focus right now.”

The omicron subvariants currently circulating are less likely to cause serious illness, health experts say, while warning that the next variant could be more dangerous.

So experts say it’s too soon to let down your guard entirely. The city health department continues to credit warnings in early April about rising case counts as the push residents needed to protect themselves even before the mandate went into effect.

“We believe that Philadelphians understand that it’s prudent to wear masks and take extra precautions when cases are rising and hope to see cases level off again or even begin to drop,” Rankin said.

But community immunity, both from prior infections and vaccination — Philadelphia boasts more than 77% of all adult residents fully vaccinated — likely has made the biggest difference, Zurlo said. Highlighting the value of the region’s growing immune resilience to COVID, the highest count of deaths during the peak of each wave of infections has become an increasingly smaller percentage of the highest count of cases.

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Sweet was ambivalent about the city’s decision to end a masking requirement more than two weeks ago. COVID still poses a serious threat to people who are vulnerable due to age or health conditions that compromise their immune systems.

“Purely from an infectious disease, public health standpoint, yeah, I think we should have kept it,” to protect the most vulnerable people, she said. “From an economic and mental health viewpoint I also see the need to try to get back to normal.”

Effective public health, though, doesn’t typically rely on mandates except in dire circumstances, Kolker said. It is encouraging, she said, that she still sees plenty of people on public transportation and in public buildings wearing masks even though it’s no longer required.

“Ideally you don’t want a mandate,” she said. “You tell people to stop smoking because it’s bad for them and you tell people to wear condoms because it’s good for them. That’s mostly how you want public health to work.”