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As Delta Spreads, Virus Cases Rise in New York City

But because of vaccines, health experts don’t expect the recent increase to reach the levels seen in New York City’s first and second waves.

A mobile vaccination site in Brooklyn last month. In the past week, New York City had a stretch of several days of 400 or more coronavirus cases.Credit...Michael M. Santiago/Getty Images

Fueled by the Delta variant, daily coronavirus case counts in New York City have begun climbing in recent days, even as the city seems determined to turn the page on the pandemic.

Just a few weeks ago, there were only 200 new cases a day across the city on average, the lowest level since the early days of the pandemic. But the city has now had a streak of days with 400 or more cases. And the test positivity rate has doubled: from below 0.6 percent on average to about 1.3 percent.

Those numbers are still low, but the increase has been swift, surprising some epidemiologists and public health officials who had not expected to see cases jump so quickly after remaining level throughout June.

Still, with some 64 percent of adults in the city fully vaccinated, epidemiologists said it was unlikely that the Delta variant would create conditions anywhere near as devastating as the past two waves of Covid-19.

“Alarming is not the right word” to describe the recent uptick in cases, said Denis Nash, an epidemiologist at the CUNY Graduate School of Public Health and Health Policy. “I would say concerning.”

The Delta variant is far more contagious than the original form of the virus that swept across the city in March 2020. It is also more contagious than even the highly transmissible B.1.1.7 variant (which was first detected in Britain and since has been renamed Alpha) that edged out other variants during the city’s long second wave.

The Delta variant was detected in a few cases in New York City in February during the second wave, but really made inroads over the past two months, when there was relatively little virus circulating in the city. By the end of May, it accounted for about 8 percent of the cases sequenced by the city, and by mid-June, more than 40 percent. Yet throughout June, the number of infections stayed low, at about 200 cases a day.

Given how contagious the Delta variant is, experts are not surprised that case counts eventually started climbing. Countries around the world are experiencing a surge as a result of Delta. In the United Kingdom, with a vaccination rate that surpasses that of the United States, cases have soared, but hospitalizations have risen more slowly.

“The metrics to keep a close eye on are hospitalizations and deaths,” said Dr. Wafaa El-Sadr, a professor of epidemiology at Columbia University.

So far, those metrics have remained stable in New York City. The seven-day average number of daily hospitalizations this week has remained under 20. The city has recently seen four or five Covid-related deaths a day on average.

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Officials hoped that a parade celebrating essential workers earlier this month would help kickstart a summer of low virus numbers. Credit...Gabriela Bhaskar/The New York Times

The hope, if not expectation, had been that the summertime would be a time of few cases. Case counts stayed low in New York last summer as the city emerged from a devastating first wave. That did not change until September, when rising transmission in a few spots in Brooklyn and Queens preceded a citywide increase in cases that eventually became a second wave that lasted until spring.

In interviews in recent weeks, some epidemiologists said they were expecting a calm summer followed by an uptick of cases around the time students returned to school and Manhattan office workers migrated back to the office.

But in the last week of June, the number of people testing positive suddenly jumped, crossing 300 on June 30. A four-day streak of 400-plus cases followed last week.

“We’ve seen some increase in cases and positivity, but we’ve also seen hospitalization rates continue to go lower,” Mayor Bill de Blasio said this week.

In news conferences, health officials have tended to focus on one borough where vaccination rates are below the city average, wearing masks is unpopular and positivity rates tend to exceed the city average — as they have for much of the past year.

“In Staten Island, the percent positivity and the case numbers have increased in recent days and weeks,” the city health commissioner, Dr. Dave Chokshi, said on Monday. “And that’s because we have unvaccinated individuals, particularly younger people, who remain unvaccinated.”

But the uptick goes far beyond Staten Island. Case counts have climbed significantly in every borough. In Brooklyn, average daily case counts nearly doubled in recent weeks from under 60 to more than 100. On Tuesday, the ZIP code that had the highest average positive test rate in the city, at 4.89, was in Harlem.

Health officials have said the vast majority of those testing positive have not been fully vaccinated.

The Health Department has not yet released statistics on how many new cases are among people who are fully vaccinated. Data from other countries shows that a full regimen of the vaccines in use in New York offers a high degree of protection against the Delta variant.

Still, breakthrough cases are not difficult to find. Stories of them circulate on Twitter, and at clinics and other testing sites.

Tony Smith, a 31-year-old Brooklyn resident who works for a social impact company, thought he was done with Covid this spring, when he got his two doses of the Pfizer vaccine. He had already caught the virus during New York’s initial wave, suffering a range of symptoms, including chest pain. For months afterward, his resting heart rate was elevated.

After his second shot of the vaccine, his heart rate dropped and he began to feel normal.

Then on Sunday, he woke up feeling slightly sick. The next day his heart rate felt higher. And he felt the same terrible sensation in his chest as he did when he first had Covid-19. “It’s like the crinkling of aluminum foil in my chest,” Mr. Smith said.

He tested positive for the virus again on Monday.

So far, he said, his symptoms felt much milder compared with his first infection. “I can tell you right now, it’s hugely comforting to have been vaccinated,” he said.

So far, the Delta variant has not led the city to drastically change its public health guidance or virus-related restrictions. Nor has it affected the plans of many large companies to get workers back to their desks in Manhattan, according to Kathryn Wylde, president of the Partnership for New York City, a leading business association.

“It would have been prudent for our elected officials to have specified in advance if, when and under what circumstances they would walk back certain components of opening up,” Professor Nash said.

For now, the city’s main strategy against Delta is to continue urging the unvaccinated to get vaccinated. But in recent months, the number of doses administered has fallen precipitously.

While vaccination rates are high in the lower half of Manhattan, much of Queens, and parts of Brooklyn, they lag behind elsewhere, especially in Black and ultra-Orthodox Jewish neighborhoods.

Already there have been sharp racial disparities in the infection rate and death rate through the first two waves of the pandemic, with the virus hitting Hispanic and Black New Yorkers hardest. Those disparities could grow even more pronounced now with Delta, given the uneven vaccination rates.

“With the Delta variant we can expect to see outbreaks in ZIP codes where African Americans live because of the low vaccination rate,” said Dr. Kitaw Demissie, who is dean of the School of Public Health at SUNY Downstate Medical Center in Brooklyn.

In interviews, epidemiologists said that to anticipate what might happen next, it was helpful to remember the 2018-2019 measles outbreak that was largely concentrated in the Orthodox Jewish communities of Williamsburg in Brooklyn. The city’s response to it was not major shutdowns, but enforcement of vaccination requirements.

“We can have localized outbreaks — similar to the outbreaks we saw with measles,” Dr. Demissie said. He expected those outbreaks to largely track areas with low vaccination rates.

The city is scrambling to figure out how to raise vaccination rates, offering in-home vaccinations and other incentives. But Mr. de Blasio has shown little interest in mandating vaccinations or pressuring people through testing requirements or other inconveniences. He has not mandated vaccinations for the city government’s 400,000-person work force, as San Francisco has.

Joseph Goldstein covers health care in New York, following years of criminal justice and police reporting for the Metro desk. He also spent a year reporting on Afghanistan from The Times’s Kabul bureau.  More about Joseph Goldstein

A version of this article appears in print on  , Section A, Page 15 of the New York edition with the headline: Variant Drives Infections Up in New York City. Order Reprints | Today’s Paper | Subscribe

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