Scientists struggle to understand the competition between Omicron and Delta

Americans feel tired and confused as the third year of the pandemic dawns. It’s all Omicron’s fault.

Scientists are unsure how fast or even if the new variant of Delta will surpass Delta. They also don’t know who will be affected by which variants and how they will get sick.

” “It does seem like Omicron changed everything we thought was known” about the virus, stated Dr. Megan Ranney , associate Dean of Brown University’s School of Public Health. “This feels like a strange turning point, potentially, in the pandemic.”

Clues about the pandemic’s next phase have begun to emerge, but they have been conflicting and prone to error. Every day, new statistics and data are poured out. But what does it all mean? Some are quite comforting, while others are deeply alarming.

Meanwhile, decisions need to be made: Visit grandma in her nursing home? Participate in the New Year’s celebration? You woke up with a sore throat and were forced to wait hours in line for the COVID test. You might send your child home within two weeks. Use a mask… everywhere?

Here are the facts and figures about Omicron, the state of the pandemic and what we don’t know.

New infections

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

The previous record was 259,759, set early last January. A week later, daily COVID-19 deaths reached their zenith of 4,048, and for the next month that figure rarely fell below 2,000. Despite how alarming this history may sound, it is unlikely that it will repeat itself. There are stark differences between now and then. Most importantly, the number of Americans who are fully vaccinated has gone from about 350,000 to more than 204 million, with 68 million of those having also received a booster shot.


Among people over 65, the vaccinated are six times less likely than the unvaccinated to be hospitalized for COVID-19. The difference is twice that for people 18 to 49. The current surge in vaccine use is a clear sign of the effectiveness of vaccines. While hospitalizations climbed almost 20% in the week that ended Monday, hitting a daily average of 9,442, that figure is 43% below the peak nearly a year ago.

Similarly, with an average of 1,085 deaths a day over the last week, COVID-19 is killing about half as many people as it did during last winter’s surge. It’s not clear how this surge in cases will unfold, as it usually takes between two and four weeks for an illness to reach a hospital. Those who die of COVID-19 often spend weeks in the hospital before succumbing. Researchers will need to search through medical records and genetic data in order to determine if Omicron or Delta had any effect on the patient’s death rate. They also have to look into how vaccines and variant types interact. This work can take several weeks or even months.

In the meantime, scientists in countries that have had the Omicron variant for some time have provided a glimpse at the future.

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

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

Omicron’s quest for dominance

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

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

News reported that Omicron’s sudden acquisition was a fact accompli, rather than the projection. Reports suggested that Omicron’s sudden takeover was also responsible for other surprising developments. New cases outnumbered those in the September wave and national intensive care units had reached three quarters of their capacity. The projection was incorrect.

A week later, the CDC would downgrade Omicron’s presence on Dec. 18 to an estimated 22.5% of new U.S. cases, predicting that by Christmas Day that figure would hit 59%. This projection could change.

Omicron is not able to perform the spectacular coup that was announced, even though it is still more transmissible than Delta. What is the story?

The CDC oversees the sequencing of about 80,000 specimens a week — about 14% of new cases, at last count — but it takes weeks to compile the results. This is too slow to allow public health officials to guide current policy.

The agency’s modelers have to take three-week-old data, and make predictions about the likelihood that this mix of variants has changed. This exercise is called “Nowcasting” and uses a mix of older genetic sequencing results provided by the states to update a variant’s national growth rate. However, a simple mistake in a fluid environment can result in serious errors if you choose the wrong sample.

The big takeaway is that the Delta variant of the virus is still present.

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

” I hear Omicron is mild and not a major concern, and that it will be dealt with quickly, Guest stated. But clearly Delta is still there, and everyone took Delta very seriously. It makes sense from the hospitalizations we’re seeing that there’s more Delta going on than we had estimated.”


The Biden administration announced this month that it would make at-home testing readily available. This is done to make it easier to determine if someone is infected and to stop the spread of the disease.

However, it will likely add to the uncertainty surrounding our understanding of the pandemic. This is because fewer people will be able to undergo PCR tests.

Proof of PCR testing has been used to detect pandemic hotspots, measure vaccine protection, determine the transmissibility and alert authorities to upcoming deaths and hospitalizations. To gain insight into individual and collective vulnerabilities, researchers also monitor what happens following a positive PCR test. This includes asymptomatic illness (asymptomatic), hospitalizations, deaths, and long COVID. All of this will be less reliable as more Americans will use at-home antigen testing, whose results won’t be centrally compiled. Some individuals may want to confirm a positive antigen test result with a PCR. Most people will not get an antigen test positive, so there won’t be many more cases.

“Testing is already shifting, and it’s likely that it’s already impacted our case counts accuracy,” Ranney stated.

She said that the DIY nature of diagnosing an illness “is partly the natural evolution in handling this virus.”

If the Omicron variant is milder and vaccines continue their protection against severe illness, mild illness will likely follow positive antigen tests. The CDC could then focus on the number of deaths and severe illnesses. Ranney stated that we will have to be more sophisticated in our thinking about this virus.

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