The US probably has 2,000 Omicron cases already, according to 'dirty math' from a COVID expert who often advises the White House

• The CDC says Omicron is not in the US yet.
• But Dr. Charity Dean, a former top health official in California, who warned about the spread of COVID-19 in the US early on in the pandemic and long before federal experts did, says there's no way that's true.

Dr. Charity Dean has a solid track record of knowing what's up when it comes to watching the coronavirus move around the world, and then forecasting what that means for how the virus is spreading through the US.

Dean, a former top-tier official at the California Department of Public Health, was one of the first people to sound the alarm that the coronavirus was alive and moving around the US in early 2020, among people with no travel history to China, where the coronavirus was first discovered.

Her warnings in those early days of the pandemic became so prescient that she was chosen to star in Michael Lewis's latest book, "The Premonition."

White House staffers in the Trump Administration, as well as the nation's top infectious disease advisor, Dr. Anthony Fauci, listened in on briefing calls where she sounded the alarm as early as February 2020.

Now that Omicron is on the scene, a new variant with a dizzying number of fresh mutations, Dean is once again attempting to warn people that the new viral variant might already be in their backyard.

"I have no doubt that there are in fact cases here in the US right now," Dean told Insider of Omicron. "In fact, my dirty math based on a number of assumptions, including international travel — I would estimate there's around 2,000 cases in the US right now."

Dean bases that assumption on the fact that the Omicron variant has already been found at least 20 countries around the globe, including South Africa, Botswana, Hong Kong, the Netherlands, Canada, and the UK. At least 226 cases have already been confirmed, according to the White House. Given that wide spread, Dean suspects the only real reason the US hasn't found Omicron within its borders yet is simply because the country is not looking hard enough for the new variant.

"The challenge for the United States is we are not doing a sufficient amount of genomic sequencing to have detected that," Dean said.

The US is "not quite there yet" when it comes to sequencing

America's viral surveillance has ramped up significantly since the early days of the pandemic, when the US was sequencing less than 1% of coronavirus cases.

Dean says this means "the United States is on the right path" when it comes to viral surveillance, "but we're not quite there yet."

Over the past six months, the US has sequenced and shared nearly 7% of its positive COVID-19 tests, though sequencing capabilities are unevenly spread across the country, meaning surveillance is far better in some areas than in others. Recently, labs haven't been doing as much sequencing as they once were, either. After all, sequencing machines cost hundreds of thousands of dollars to procure, and once health departments do, it generally takes at least 24 to 48 hours to sequence a single sample.

"So many labs ramped down their sequencing efforts, understandably, throughout the Delta surge, when everything was the Delta variant," Dean said.

That cost-saving move means it's harder to be on alert for Omicron now.

"The challenge with having an inadequate amount of genomic sequencing in the US is it makes it much harder to detect a novel variant when it emerges," she said.

The UK and southern Africa have more efficient systems to track Omicron

The Centers for Disease Control and Prevention is confident that the country is standing ready to find the new variant as soon as it may arrive.

"We are actively looking for the Omicron variant right here in the United States," CDC Director Rochelle Walensky said during a White House COVID-19 briefing on Tuesday. "Our variant surveillance system has demonstrated we can reliably detect new variants."

But the reality is that other nations (including South Africa and the UK) have far better health systems in place, to not only sequence the virus, but then link up that information with a person's vaccine status, as well as whether or not they're hospitalized, and how severe their case is.

"Right now, there is no evidence of Omicron in the United States, the Delta variant remains the predominant circulating strain, representing 99.9% of all sequences sampled," Walensky said.

Dean, however, interprets the same finding quite differently.

"Right now, the US has zero detected cases of Omicron, which means our case ascertainment rate is zero," she said. "Genomic sequencing and genomic epidemiology is the disease control of the future."