The number of new Covid-19 cases in New York City rose more than twenty-fold in December. In the past few days, it has flattened. In both New Jersey and Maryland, the number of new cases has fallen slightly this week. In several major cities, the number is also showing signs of levelling off.

In Boston, the amount of the Covid virus detected in wastewater, which has been a leading indicator of case trends in the past, has plunged by about 40 per cent since its peak just after January 1.

“We really try not to ever make any predictions about this virus, because it always throws us for a loop,” Dr Shira Doron, an epidemiologist at Tufts Medical Center, told GBH News. “But at least the wastewater is suggesting a steep decline, and so we hope that means cases will decline steeply as well, and then hospitalisations and deaths will follow.”

As Doron suggested, it’s too early to be confident that the omicron wave has peaked even in areas with encouraging data — which tend to be the places where omicron first arrived in the US. But there is good reason to consider that the most likely scenario. “Looks like we may be cresting over that peak,” governor Kathy Hochul of New York said this week.

A huge surge in cases that lasts for about one month, followed by a rapid decline, would be consistent with the experience in some places where omicron arrived earlier than in the US. In South Africa, new daily cases have fallen by about 70 per cent from the mid-December peak. The chart showing South Africa’s recent trend looks like a skinny, upside-down letter V.

In Britain, where pandemic trends have frequently been a few weeks ahead of those in the US, cases peaked just after New Year’s and have since fallen somewhat:

With previous versions of Covid, like the Delta variant, the up-and-down cycles tended to last longer. Once an outbreak began, cases often rose for about two months before falling.

Scientists don’t fully understand Covid’s cycles, but the explanation probably involves some combination of the virus’s biological qualities and the size of a typical human social network. After about two months, an outbreak of earlier variants began to burn out, much as a forest fire would.

Omicron is so contagious that it spreads more quickly. This rapid spread may also mean that it more quickly reaches most of the people who happen to be vulnerable to being infected by it.

Ali Mokdad, a professor of health metrics sciences at the University of Washington, Seattle, said he believed the true number of US cases — including those not included in any official tally — has already peaked, probably last week. “It’s going to come down as fast as it went up,” he said.

(New York Times News Service)