The city’s recent slow and steady rise in cases has been fueled, as it has nationally, by social gatherings dating to early fall, said Dr. Denis Nash, an epidemiologist at the City University of New York. Among the causes were gatherings for the Jewish high holidays in September, Halloween and the winter holidays, though the rise in cases post-New Year’s was less steep than feared.
“I see the cumulative effect of all the extra interactions,” Dr. Nash said.
At the current rate of vaccination, experts say, it will take months to change the virus’s trajectory. In the short term, they worry that the vaccine could present new risks if newly immunized people start socializing without taking precautions. It is not yet clear if the vaccine protects against asymptomatic infection, so vaccinated people may still be able to spread the virus to others.
It is difficult to say just how New York compares with other states. On Friday, by cases per capita, New York State was a hot spot, with the fourth highest rate of coronavirus cases per 100,000 residents in the country, according to New York Times tracking data.
That rate is declining, however, and cases nationally have fallen by more than 20 percent in the last two weeks, according to a Times database.
By positive test rate, a measure that Dr. Frieden said was more predictive of risk, New York was still in the lowest third of states, at 6 percent positivity, according to Johns Hopkins University’s coronavirus tracking data.
That level is still a far cry from the summer, when New York’s steady, 1 percent positivity rate was a source of pride for Mr. Cuomo and one of the lowest in the nation. On Thursday, New York City’s own calculation for its seven-day positivity rate placed it at just over 9 percent.