Scientists are struggling to understand the competition between Omicron and Delta



When the third year of the pandemic arrives, Americans feel tired and confused. And it’s all Omicron’s fault.

Even scientists are deeply unsure about how quickly or even whether the new variant will eclipse Delta, as well as who is likely to get sick with which variant and how these sick people will get.

“It looks like Omicron has changed everything we thought we knew about the virus,” said Dr. Megan Ranney, an associate dean of Brown University School of Public Health. “This feels like a potentially strange turning point, potentially, in the pandemic.”

Clues have begun to emerge about the next phase of the pandemic, but they have been conflicted and prone to error. Torrents of new data and statistics are falling every day, but what they mean is not always clear. Some seem quite reassuring, others deeply alarming.

In the meantime, decisions need to be made: should Grandma visit her nursing home? Are you attending the New Year’s Eve meeting? Waiting for hours queuing for a COVID test because you woke up with a scratched throat? Will you send your child to college when he or she can be sent home in two weeks? Wear a mask … everywhere?

This is what we know about Omicron and the state of the pandemic, and what we don’t.

New infections

The United States has reached a new high of confirmed infections, averaging 277,241 new cases a day during the last full week of 2021.

The previous record was 259,759, set in early January. One week later, daily deaths from COVID-19 peaked at 4,048, and during the following month that figure rarely dropped below 2,000.

As worrying as the story may seem, it is unlikely to be repeated, because there are big differences between then and now. Most importantly, the number of fully vaccinated Americans has risen from about 350,000 to more than 204 million, and 68 million of them have also received a booster vaccine.


Among people over the age of 65, those who are vaccinated are six times less likely than those who are not vaccinated to be hospitalized with COVID-19. The difference is twice that of 18- to 49-year-olds.

The benefit of vaccines seems evident in the current increase. While hospitalizations rose nearly 20 percent in the week ending Monday, averaging 9,442 a day, that figure is 43 percent below a year-high high of almost a year ago.

Similarly, with an average of 1,085 deaths a day over the past week, COVID-19 is killing about half as many people as during last winter’s increase.

However, it is unclear how the increase in cases will occur, as it usually takes two to four weeks for an infection to send a person to the hospital. Those who die from COVID-19 often spend weeks in the hospital before succumbing.

And even after hospitalization and mortality rates are known, researchers will need to review medical records and genetic data to compare the effects of Omicron and Delta, and how vaccination and variant type interacted. This job could take weeks or months.

Meanwhile, site researchers who have hosted the Omicron variant for a little longer than the United States have offered a possible vision for the future here.

An analysis by South African scientists suggests that people who were thought to be infected with Omicron were about 70% less likely to become seriously ill and 80% less likely to be hospitalized than those who were infected with Delta.

A study in England found that after considering the effects of vaccination, people infected with Omicron were 45% less likely than people infected with Delta to end up in hospital.

Omicron domain search

It is unclear whether current trends are being driven more by the Omicron variant or the Delta variant.

On December 22, a projection released by the U.S. Centers for Disease Control and Prevention suggested that Omicron had skyrocketed in U.S. dominance, from 3% of all cases to 73% in two weeks. December.

The news treated Omicron’s sudden takeover as a consummate fact rather than the projection it was. Reports also seemed to suggest that the new variant was responsible for other shocking advances: new cases had surpassed those seen in last September’s wave, and nationwide intensive care units had reached about three-quarters of capacity.

It turned out that the projection was incorrect.

One week later, the CDC would reduce Omicron’s presence on December 18 to an estimated 22.5% of new U.S. cases, predicting that on Christmas Day that figure would reach 59%. This projection could also change.

While still much more transmissible than Delta, Omicron doesn’t seem to have performed the impressive blow that was announced. What happened?

The CDC oversees the sequencing of about 80,000 copies per week (approximately 14% of new cases, in the last count), but it takes weeks to collect the results. This is too slow for public health authorities to guide current policy.

Therefore, agency modelers need to take three-week data and make judgments about how this combination of variants is likely to have changed. This exercise, known as “Nowcasting,” uses some of the most recent genetic sequencing results provided by states to update a variant’s national growth rate. But choosing the wrong sample, an easy mistake in a very fluid situation, can lead to significant mistakes.

The big takeaway: the Delta variant is still very much among us.

Emory University epidemiologist Jodie Guest said that in the face of an increase in new cases, Delta is likely to do what it has done since its arrival last March: send many who remain unvaccinated in the United States. ‘hospital, or worse.

“I usually feel like Omicron is mild, that it won’t be a big deal, and I hope it’s true,” Guest said. “But it’s clear that Delta is still here and everyone took Delta quite seriously. It makes sense from the hospitalizations we’re seeing that there’s more Delta than we’d estimated.”

Try it

The Biden administration announced this month that it would make the tests at home readily available. The aim is to make it easier for people to find out if they are infected and take action to prevent the virus from spreading.

But it is also likely to add another layer of uncertainty to our understanding of the pandemic, because it means fewer people will receive PCR testing.

Collected from all corners of the United States and zealously tracked by the CDC, positive PCR tests have been the basis for detecting pandemic hotspots, measuring vaccine protection, finding out the transmissibility of new variants, and alerting authorities. upcoming waves of hospitalizations and deaths. Researchers are also tracking what happens after a positive PCR test (asymptomatic illness, hospitalization, death, long-term COVID) for information on individual and group vulnerabilities.

All of this will become less reliable as more Americans use antigen tests at home, the results of which will not be compiled centrally. Some people who get a positive reading on an antigen test may try to confirm it with a PCR test. But most will probably not, which means more infections will not go into the official case count.

“The evidence has already begun to change and is likely to have already affected the accuracy of our case count,” Ranney said.

At the same time, the increasingly DIY nature of diagnosing an infection “is in part the natural evolution of the management of this virus,” he said.

If the Omicron variant proves to be milder and the vaccines continue to protect against serious disease, positive antigen testing will be largely followed by a mild disease. At this point, the CDC could focus more on counting serious illness and death.

“We need to be more sophisticated about how we think about this virus,” Ranney said.

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