CDC estimates Omicron now accounts for 73% of US COVID cases

A new report from the Centers for Disease Control and Prevention (CDC) indicates the Omicron variant is now dominant in the United States. The CDC’s variant-tracking model found Omicron has skyrocketed in prevalence over the course of two to three weeks.

The CDC’s national genomic surveillance system analyzes SARS-CoV-2 samples from all over the country. Thousands of viral genomic sequences are studied every week allowing for confident surveillance of emerging viral variants.

The latest variant surveillance update, for the week ending 18 December, estimates Omicron accounts for 73.2 percent of SARS-CoV-2 cases in the US. This is up from the previous week’s estimate of Omicron accounting for 12.6 percent of cases.

Because comprehensive genomic sequencing data usually takes one to two weeks to collect, the CDC has incorporated a model called Nowcast to estimate current variant proportions. Last week’s Nowcast estimate only projected Omicron accounting for 3 percent of US cases but that has since been updated to 12.6 percent.

Data from two weeks ago, now up to date with real-world genomic analyses, indicate Omicron was only accounting for 0.7 percent of analyzed cases for the week ending 4 December. This is an extraordinary growth rate for a viral variant that was only discovered and characterized in late November.

Across the country the prevalence of Omicron varies, according to CDC data. New York, for example, is registering some of the highest rates with over 90 percent of cases estimated to be Omicron, while California is only estimated to have around 60 percent Omicron prevalence.

It is important to note these Nowcast estimates are just projections based on prior models, so these numbers are likely to shift over the coming days as real genomic data comes in. However, the CDC modeling does suggest these projections are more likely to be underestimates of Omicron’s prevalence, as seen with last week’s estimate rising from three to 12 percent.

Speaking to CNBC, Rochelle Walensky, director of the CDC, says this growth rate was expected after seeing how rapidly Omicron has spread in countries around the world. While there is still significant uncertainty surrounding the severity of disease generated by the Omicron variant, Walensky notes there are many reasons people should try to avoid being infected beyond their own individual risk for illness.

“We don’t know yet the long term manifestations of Omicron, the long COVID that we’ve seen with other variants,” she says. “As well as the fact you could transmit it to other people who are more immunocompromised, older people, family members.”

Michael Osterholm, an infectious disease expert from the University of Minnesota, pointed out to CNN his concern with Omicron’s rapid growth. Even if Omicron leads to milder disease in many people, Osterholm says the disruption to health care systems from absent staff could be disastrous if lots of people were to be infected in a short period of time.

“We are going to see 20 percent, 30 percent of health care workers getting infected, who will then be off of work in a health care system right now that is already stretched to the point of breaking,” says Osterholm.

Source: CDC

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