COVID cases drop sharply in 4 northeastern states. An indicatiuon of herd immunity?

Eager to know when parts of America are finally approaching herd immunity against COVID-19? Then pay close attention to what’s happening in New York, New Jersey, Massachusetts and Connecticut.

Triggered by reopenings and fueled by the rise of more contagious variants, COVID numbers suddenly shot up across all four states last month. But then, just as suddenly, cases began to plummet right at the start of April — and they’re still plummeting today, even as restrictions are being lifted.

Could this swift reversal — which occurred despite rising mobility and mixing — herald the local onset of something like herd immunity (that is, the point when the virus starts to run out of unprotected hosts to infect)?

“I do think this pattern is significant, and the leading factor is the combination of natural immunity from infection and vaccine-induced immunity,” says Yahoo News Medical Contributor Dr. Kavita Patel, a Brookings Institution health scholar and a primary care internist. “Between the two, you’re starting to cover the majority of the population in these states. We’re progressing toward herd immunity kind of by hook or crook.”

We may never actually know when a particular state (or the U.S. as a whole) crosses the herd immunity threshold, which experts describe as the point when 75 to 90 percent of a particular population is protected by antibodies. For one thing, true herd immunity — the goal of getting so many Americans vaccinated that COVID-19 can never spread again — is probably unattainable; vaccine demand is declining, hesitancy persists in certain pockets of the country, variants keep emerging and most of the rest of the world remains unshielded by prior infection or immunization. ....

This is not to say that the pandemic isn’t still raging across the country. “I do not think we are even close to real herd immunity,” Howard Forman, a professor of public health at Yale University, tells Yahoo News.

To his point, cases continue to rise in states such as North Carolina, Oregon and Nevada — and on Thursday, Washington Gov. Jay Inslee said his state, which was also hit hard last spring, is “seeing the beginning of a fourth surge” that is “starting, unfortunately, at a higher level than where the other waves started from.”

Still, “the more people who are immune,” Forman explains, “the less steep the inclines.” ...

Which is where New York, New Jersey, Massachusetts and Connecticut come in. 

... since the start of April, average daily cases have declined by 46 percent in New York, 29 percent in New Jersey, 30 percent in Massachusetts and 40 percent in Connecticut — even as rules on bars, restaurants, movie theaters and other businesses have been getting looser and looser.

Testing across all four states, meanwhile, has hovered around the same level for months, suggesting that the actual number of infections is falling, as opposed to just the number of infections being detected. 

The question is, why now? ...