Public health authorities in Denmark and Norway on Monday released grim projections for the coming wave of the Omicron coronavirus variant, predicting that it will dominate both countries in a matter of days. Although scientists don’t yet know how often the variant causes severe disease, they say its rapid rate of spread will lead to an explosion of cases and could potentially increase pressure on hospitals, even if it proves to be mild.
The reports follow similarly worrisome findings from England released over the weekend, although researchers caution that the trend could change as the variant comes into clearer view. It’s not yet certain how often Omicron infections will send people to the hospital, or how many hospitalized patients are likely to die. And while Omicron can partly evade immune defenses, researchers have yet to determine how well vaccinations and previous infections will protect people against severe disease.
The authors of both new reports also observed that swift actions now, such as booster campaigns and reducing opportunities for Omicron to spread, could lessen the variant’s impact.
American researchers have yet to release models of Omicron’s rise in the United States. But experts point out that the country is similar to Norway and Denmark in terms of vaccination levels and certain Covid risk factors, like the average age of the population.
“It would be naïve to think the United States would be any different than Denmark,” Mads Albertsen, a microbiologist at Aalborg University, said. “Denmark is likely a best-case scenario.”
In recent weeks, many epidemiologists have been paying close attention to Denmark, a country of 5.8 million residents, about the population of Wisconsin.
Early in the pandemic, the country set up a sophisticated surveillance system combining large-scale coronavirus testing with genetic sequencing of many samples. That strategy has allowed Denmark to spot newly emerging variants, even when they’re at low levels, and adjust public health policies to prepare for new surges.
The first Omicron sample from Denmark was sequenced on Dec. 3. The specimen was collected on Nov. 23, around the same time researchers in South Africa first told the world about a rise in cases there.
Because sequencing genetic material from coronavirus samples can take days, Danish researchers developed a quick genetic test that picks up a few key mutations found only in Omicron. Every positive test result in Denmark is now screened for the new variant, resulting in an exceptionally comprehensive picture of Omicron’s spread.
In the report released on Monday by the Statens Serum Institute in Copenhagen, researchers estimated that Omicron cases in Denmark were doubling every two days. Omicron is spreading much faster than Delta, which means that the new variant will become dominant by midweek, the report found.
Three-quarters of the Omicron cases are in people who have received two vaccine doses, which is about the same fraction of the entire country that’s fully vaccinated. That high percentage indicates that vaccines are providing little protection from infection, though most scientists believe that the shots will still fend off severe disease and death.
The Danish data are consistent with a smaller report of Omicron infections in the United States. Out of 43 documented cases, 34 — or about 79 percent — were people who were fully vaccinated.
“This thing can spread, and it can spread whether or not you were vaccinated,” Christina Ramirez, a biostatistician at the University of California, Los Angeles, said.
In England, researchers also found that full vaccination provided low protection against a breakthrough infection. But they found that booster shots restored defenses to much higher levels.
In these European countries, Omicron will not simply replace Delta: It will drive up cases. Currently, Denmark is seeing around 6,000 cases a day — already a record for the country and driven almost entirely by Delta. The Danish researchers project that Omicron will drive the daily cases to 10,000 by the end of the week, and the numbers will continue to climb from there.
The model predicts that the explosive growth could send large numbers of people to the hospital, even if the Omicron variant turns out to be milder than earlier variants. The Danish researchers also warned that Omicron outbreaks at hospitals, even if mild, could lead to dangerous drops in staffing as doctors and nurses are sent home to quarantine.
The authors of the new report cautioned that their model was preliminary. It did not take into account the potent protection that boosters can afford, for example. Right now, 21 percent of people in Denmark have gotten a booster shot, and the country is pursuing an aggressive booster campaign.
Even so, Troels Lillebaek, the director of the Statens Serum Institute, said that the next few weeks would be a major challenge for the country’s hospitals.
“Regardless of the uncertainty about the precise severity and contagiousness of Omicron, there is a very high risk of an increasing number of admissions,” he said.
In Norway, researchers have also observed a rapid rise of Omicron in recent days. “The Omicron variant is becoming established in Norway and will soon dominate,” the Norwegian Institute of Public Health said in a statement on Monday.
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In a preliminary scenario, the institute estimated that in about three weeks, there would be up to 90,000 to 300,000 cases per day — a stark increase from the current pace of about 4,700 cases per day, a record for Norway.
The Norwegian researchers also said this could lead to significantly more hospital admissions, even if Omicron is milder. They project that Norwegian hospitals will see 50 to 200 admissions each day, unless swift measures slow the epidemic significantly. Right now, Norway is seeing about 30 admissions each day, which are already enough to put a strain on the country’s hospitals.
“There is an urgent need to curb the Covid-19 epidemic with significant measures so that the Omicron variant does not cause an epidemic wave that places an enormous disease burden and completely overloads the health service,” the Norwegian Institute of Public Health warned.
Last week, Denmark imposed new public health restrictions, including requiring restaurants and bars to close at midnight and switching some schools to virtual instruction before the winter holidays. It is also accelerating its booster campaign. People who are 40 or older and at least four and a half months past their second shot are now eligible for a third dose, the Danish Health Authority said on Monday.
The Norwegian government also sped up its booster rollout and announced other new measures on Monday, though it stopped short of a full lockdown. The new measures include indoor mask mandates, a ban on serving alcohol, restrictions on social gatherings and social distancing requirements at organized events.
Omicron will probably spread quickly through the population in the United States as well, said Dr. Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington, which is planning to release its Omicron models later this week.
“I would expect that we’ll see Omicron in the U.S. becoming really the dominant strain end of the month or in January sometime,” he said.
But because so much remains unknown about the variant’s severity, it is difficult to predict how its spread will affect hospitalizations.
“There’s a very big range of possible outcomes here,” Dr. Murray said.
One key metric will be whether cases and hospitalizations rise in tandem in the coming weeks; if hospitalizations increase much more slowly than cases, that will be a good sign, he said.
But even if Omicron turns out to be relatively mild, its rapid spread could still put a heavy burden on hospitals, experts cautioned.
“Imagine that it spreads so fast that it produces an outbreak that peaks with twice as many people infected, yet it’s half as likely to put somebody in the hospital,” said Jeffrey Shaman, an infectious disease epidemiologist at Columbia University. “Well, that’s a wash. That means that you’d see the same kind of crush that we saw last winter.”
A surge of Delta cases is already hurting some hospitals, and Omicron’s arrival also coincides with flu season, Joshua Salomon, an infectious disease expert and modeler at Stanford University, said.
“An Omicron surge on top of a Delta surge, at the same time that there might be rises in flu cases, is a very worrisome combination,” he said.
Henrik Pryser Libell contributed reporting from Oslo, and Jasmina Nielsen from Copenhagen.