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How long will omicron last? Variant cases could peak by mid-January.

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.

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?

The latest coronavirus variant has taken over as the dominant strain in the U.S. Here’s what we know about omicron. (Monica Rodman, Sarah Hashemi/The Washington Post)

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 S. Fauci, President 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.

That has led to a shift in the Biden administration’s strategy, with a new emphasis on keeping the economy running and shying away from top-down restrictions. All the while, the administration continues to push the available tools for fighting the pandemic, including testing, indoor masking, vaccinations for those reluctant to get the shots and boosters for those eligible for another dose.

But a more spontaneous shutdown has been underway since just before Christmas.

Airlines have canceled thousands of flights because of staffing shortages. The Smithsonian closed a few of its smaller museums. Some college football teams decided not to attend their bowl games. Broadway shows have gone dark. Actor Hugh Jackman, mildly sick with covid-19, is not anticipated back onstage in “The Music Man” until Jan. 6.

This is a new phase of the pandemic, one with sweeping disruptions but probably not the same level of fear and anxiety as earlier periods. Omicron appears milder. For many vaccinated people, it appears to present itself more like a bad cold than something capable of crippling the world economy — although the ramifications of the phenomenon known as “long covid” remain not well understood.

Scientists don’t know precisely why omicron tends to cause less severe illnesses than delta or other variants of the coronavirus. It is likely that immunity plays a role, as so many people have been infected previously or have been vaccinated.

That appears to have been the case in South Africa, hard hit by the virus in advance of the omicron wave.

A study of more than 7,000 people, posted online but not yet peer-reviewed, reported high levels of antibodies to the coronavirus in South Africa before the omicron wave. Omicron spread faster than previous variants, but rates of hospitalizations and excess deaths “did not increase proportionately, remaining relatively low,” the study found.

Research on mice and hamsters suggests that omicron is innately less dangerous, apart from population immunity. Although omicron appears to grow especially well in the nose and upper airways, leading to much higher viral loads and easier transmission, it may not invade the lungs as well as earlier variants.

“The dam has broken with a milder variant. Most people who made the correct choice to get vaccinated are protected from severe disease,” said David Rubin, director of PolicyLab at Children’s Hospital of Philadelphia.

Rubin predicts a swift recovery for much of the country in January but notes this is likely to vary geographically. The East Coast, including major cities along the Interstate 95 corridor, and the heavily populated states of Florida and Texas are seeing large spikes in cases, while parts of the country hit hard by delta, including the Upper Midwest, are already seeing improvements, he said.

“By the second week of January, we’re going to see the national declines, but there will be some areas struggling for sure,” Rubin said.

A model from the Institute of Health Metrics and Evaluation at the University of Washington puts the peak of this winter wave at Feb. 6, with 408,000 confirmed new daily infections.

Pandemic models are hampered by the difficulty of amassing reliable data. Testing is disrupted during the holidays. There are only rough estimates of how many people have already been infected.

The most urgent question is whether a spike in caseloads will lead to so many severe illnesses that hospitals are overwhelmed. Although some hospitals are stretched thin, the increase in hospitalizations has been modest so far compared with the rise in infections.

For now, the Biden administration is holding off on drastic measures to combat omicron, beyond common-sense efforts to get more tests in the hands of the public and to encourage vaccination. CDC has issued looser rather than tighter guidelines on the isolation time for people infected with the virus, reducing the recommendation from 10 days to five.

That covers people who are asymptomatic or are seeing their symptoms improve. The CDC’s guidance does not advise that people get a negative test before leaving isolation.

The virus has never been a static agent, nor is society a monolith, and so any forecast of what will happen in the coming weeks needs to be written with a pencil — not a pen.

Shaman, the Columbia epidemiologist, acknowledges that the model he and his colleagues have developed is based on incomplete data and must take into account a new variant that remains somewhat enigmatic.

And the virus itself may have new moves not yet anticipated.

“I’m not a betting person on this thing, ever,” Shaman said.

Jacqueline Dupree contributed to this report.

https://www.washingtonpost.com/health/2021/12/30/how-long-will-omicron-last/