The rapid surge of omicron infections in the United States may be relatively brief, measured in weeks rather than months, according to infectious-disease experts who have been astonished by the speed of the coronavirus variant’s spread – and who are hoping this wave ebbs just as quickly.

The idea of a rapid peak and swift decline has a precedent in South Africa, the country that revealed the presence of omicron in late November. Cases there spiked quickly and then dropped with unexpected speed after only a modest rise in hospitalizations. An especially transmissible virus tends to run out of human fuel – the susceptible portion of the population – quickly.

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Some forecasts suggest coronavirus infections could peak by mid-January.

“Omicron will likely be quick. It won’t be easy, but it will be quick. Come the early spring, a lot of people will have experienced covid,” William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, said in an email Thursday.

But this has always been an unpredictable virus, going back to when it first appeared two years ago, on Dec. 31, 2019. The virus had probably been spreading for a month or more, but that was the day infectious-disease experts around the world began hearing by email and text about an outbreak of a mysterious pathogen causing pneumonia-like respiratory infections in Wuhan, China.

No one on that day could have known that this pathogen, initially called the “novel coronavirus” and later named SARS-CoV-2, would trigger the most brutal pandemic in a century. And no one today knows when it will be over.

Forecasts of how the pandemic will play out have repeatedly been incorrect, to the point that some modelers have stopped trying to make caseload projections four weeks out, instead limiting their forecasts to one week ahead.

Because beyond a week, who knows?

Forecasts of the current winter wave, in which omicron has come riding in atop an existing delta wave, are somewhat more plausible. Columbia University researchers have a model that projects a peak in cases during the week beginning Jan. 9, with about 2.5 million confirmed infections in that seven-day period – and potentially as many as 5 million.

Columbia epidemiologist Jeffrey Shaman said the infection numbers reported in recent days are already at the high end of projections, and the peak could come sooner. Omicron is setting new daily records for infections with the virus. The seven-day average of new, officially confirmed daily cases soared to more than 300,000 Wednesday. Then came the eye-popping Thursday numbers from state health departments and the Centers for Disease Control and Prevention – 562,000 new cases, pushing the seven-day average to 343,000.

The official number captures only a fraction of the true number of infections. People who use rapid tests at home may not report positive results. Many others never get tested when sick. And some people are infected but asymptomatic or pre-symptomatic.

Shaman estimates the number of infections is four to five times the official count. Given that people remain infected for many days, that translates to many millions of active infections across the United States.

“We’re talking somewhere up to maybe 10 million people,” Shaman said. “Maybe not all of them are contagious yet. Crazy numbers. Crazy, crazy numbers.”

When infections begin to drop, hospitalizations could still rise for a period as the disease progresses among those most vulnerable to a severe outcome. Forecasts posted Monday by the CDC show national hospitalization rates rising steadily in the weeks ahead, with daily new hospital admissions topping 15,000 by mid-January – although the projections from different research teams varied widely.

The predictions of a short omicron surge are reflected in hopes expressed at the highest level of the federal medical bureaucracy.

“My hope is that we get a sharp peak with omicron, and it goes down to a very, very low level, and it just sort of stays there, and we don’t have any more really problematic variants,” Anthony Fauci, President Joe Biden’s chief medical adviser for the pandemic, told The Washington Post on Wednesday.

But Fauci and other experts have consistently been surprised by the mutability of the virus. Some scientists did not think a variant with the number of mutations evident in omicron could be an effective transmitter.

“We are dealing with a virus that has a completely unanticipated level of transmissibility,” Fauci said. “We thought delta was very transmissible. This thing is like something we’ve never seen before.”

In the United States, vaccinations – including boosters – have blunted much of the impact of the latest wave of infections from the omicron variant, which appears to be innately less capable of generating severe disease.

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