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Scientists struggle to understand the competition between Omicron and Delta

On the eve of the third year of the pandemic, Americans are feeling tired and confused. And it’s all Omicron’s fault.

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

“It feels like Omicron has changed everything we thought we knew” about the virus, said Dr megan ranney, Associate Dean of the School of Public Health at Brown University. “It sounds like a weird turning point, potentially, in the pandemic. “

Clues about the next phase of the pandemic have started to emerge, but they have been contradictory and prone to error. Torrents of new data and statistics fall daily, but what they mean is not always clear. Some seem quite reassuring, others deeply alarming.

In the meantime, decisions have to be made: to visit grandmother in her retirement home? Attend that New Year’s gathering? Waiting hours in line for a COVID test because you woke up with a sore throat? Send your child back to college when she could be sent home in two weeks? Wear a mask … everywhere?

Here’s what we know about Omicron and the state of the pandemic – and what we don’t know.

New infections

The United States has recorded a new record for confirmed infections, with an average of 277,241 new cases per day for the last full week of 2021.

The previous record was 259,759, set at the start of last January. A week later, daily COVID-19 deaths reached their zenith 4,048, and for the following month that number rarely fell below 2,000.

As disturbing as this story may sound, it is unlikely to repeat itself, as there are big differences between yesterday and today. More importantly, the number of Americans who fully vaccinated rose from around 350,000 to over 204 million, of which 68 million also received a recall.


Among people over 65, the vaccinated are six times less likely than the unvaccinated to be hospitalized for COVID-19. The difference is double that of 18 to 49 year olds.

The benefit of vaccines seems evident in the current wave. While hospitalizations soared nearly 20% in the week ending Monday, reaching a daily average of 9,442, that figure is 43% lower than the peak almost a year ago. .

Likewise, with a average of 1,085 deaths per day COVID-19 killed about half as many people over the past week as it did in last winter’s outbreak.

Still, it’s unclear how the increased number of cases will play out, as it typically 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 hospital before succumbing.

And even after hospitalization and death rates are known, researchers will need to sift through medical records and genetic data to compare the effects of Omicron and Delta, and how vaccination and the type of variant interact. This job can take weeks or months.

In the meantime, researchers in places that have hosted the Omicron variant for a little longer than the United States have offered a possible glimpse into the future here.

A To analyse by South African scientists suggests that those suspected of being infected with Omicron were about 70% less likely to become seriously ill and 80% less likely to be hospitalized than those infected with Delta.

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

Omicron’s quest for domination

It is not known whether the current trends are driven more by the Omicron variant or the Delta variant.

On December 22, a projection released by the United States Centers for Disease Control and Prevention suggested that Omicron had become dominant in the United States, dropping from 3% of all cases to 73% in two weeks in early December.

Reports treated Omicron’s sudden takeover as a fait accompli rather than a projection. Reports also seemed to suggest that the new variant was responsible for other shocking developments: New cases had overtaken those seen in last September’s surge, and intensive care units nationwide had reached about three-quarters of their capacity.

The projection turned out to be wrong.

A week later, the CDC would reduce Omicron’s presence on Dec. 18 to about 22.5% of new cases in the United States, predicting that on Christmas Day that figure would rise to 59%. This projection could also change.

Although still much more transmissible than Delta, Omicron does not seem to have achieved the coup he had been told. What happened?

The CDC oversees the sequencing of approximately 80,000 specimens a week – about 14% of new cases, at last count – but it takes weeks to compile the results. It’s too slow for the public health authorities who guide current policy.

So the agency’s modelers must take data that is three weeks old and make judgments about how this mix of variants is likely to have changed. This exercise, known as “Nowcasting,” uses a handful of more recent gene 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 big mistakes.

The big point to remember: the Delta variant is still very present among us.

Emory University Epidemiologist Jodie Guest said that in a wave of new cases, Delta is likely to do what it has done since arriving last March: send many unvaccinated to hospital, or worse.

“I regularly hear that Omicron is sweet, that’s okay, and I hope it’s true,” Guest said. “But it’s clear that Delta is still here, and everyone took Delta pretty seriously. It makes sense from the hospitalizations that we’re seeing that there is more Delta than we expected.”


The Biden administration announced this month that it would make home testing readily available. The goal is to make it easier for people to determine if they are infected and to take action to prevent the spread of the virus.

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

Gathered from all corners of the United States and zealously tracked by the CDC, the positive PCR tests served as the basis for detecting pandemic hotspots, measuring vaccine protection, determining the transmissibility of new variants, and alerting authorities of upcoming waves. hospitalizations and deaths. Researchers are also tracking what happens after a positive PCR test – asymptomatic illness, hospitalization, death, long COVID – to better understand individual and group vulnerabilities.

All of this will become less reliable as more Americans use home antigen testing, the results of which will not be centrally compiled. Some people who get a positive reading on an antigen test may seek to confirm it with a PCR test. But most likely won’t, which means more infections won’t appear in the official tally of cases.

“Testing has already started to change, and that has probably already impacted the accuracy of our case count,” Ranney said.

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

If the Omicron variant turns out to be milder and the vaccines continue to protect against serious illness, positive antigen tests will largely be followed by mild illness. At this point, the CDC might focus more on tallying critical illnesses and deaths.

“We’re going to have to get more sophisticated about how we think about this virus,” Ranney said.




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