Experts predicted the UK variant would become dominant in the US by March. So, is it?

Mounting evidence suggests the more contagious coronavirus variant first identified in the UK, which experts believe is partly driving an uptick of cases in places like Michigan, may already be dominant across the US.

“I think we are there,” said William Lee, vice president of science at Helix, a company whose tests have identified a large share of variant cases across the country. “But at the end of the day, it’s hard to say for sure,” given gaps and delays in the data.

Lee is one of the authors of a study published Tuesday in the journal Cell estimating that the variant, known as B.1.1.7, would cause the majority of Covid-19 cases in the US by March 19.

According to that study, B.1.1.7 cases are expected to double every week and a half as a percentage of the country’s total coronavirus cases. The study also concluded the variant was introduced several different times to the US, as early as late November. The study’s conclusions were based on testing data through February.

Lee said that there’s strong evidence the variant is already responsible for a majority of cases in states like Florida, Michigan and Georgia — with a number of others close on their heels, including Pennsylvania, North Carolina, Texas and Southern California. However, Helix’s data do not include robust samples from a number of other states, particularly in the Northeast and Midwest regions.

Notably, the study’s estimates of when B.1.1.7 would become dominant in certain individual states skewed earlier than what ultimately happened, based on CNN’s review of later data from Helix that wasn’t included in the study. Lee said the rapid rollout of vaccinations may have contributed to this, though it wasn’t accounted for in the study.

‘Starting to become the predominant variant’

While officials with the US Centers for Disease Control and Prevention won’t yet say whether the variant is dominant, its own scientists previously predicted this would be the case by now.

In January, a CDC study predicted that the variant would exhibit “rapid growth in early 2021, becoming the predominant variant in March.” At the time, the variant was assumed to account for less than 0.5% of cases.

In mid-March, CDC Director Dr. Rochelle Walensky said at a briefing, “Our current models still project, by the end of March, early April, B.1.1.7 will be the dominant variant.”

“B.1.1.7, we know from our most recent data, is about 26% of circulating virus right now,” Walensky said at another briefing Wednesday. This appears to be based on preliminary data of samples collected in the two weeks leading up to March 13, according to CDC’s website. “It is starting to become the predominant variant in many US regions,” she added.

That would mean nearly two doubling periods may have passed since then, which could put that number well over 50%. However, it is unclear to what extent these numbers might be influenced by the fact that B.1.1.7 is easier to find than other variants, because of a glitch that shows up on certain PCR tests for Covid-19.

A CDC spokesperson told CNN Wednesday that “national prevalence estimates are inherently delayed by a few weeks.” While the present-day picture of the variant is “unclear,” they said the agency expects to share its projections “in the near future,” based on mathematical modeling that’s currently underway.

Nearly 12,000 cases of the variant have been identified in 49 states, Puerto Rico and Washington, DC, per CDC. The agency says this does not represent the total number of such cases circulating in the US, but rather just those that have been found by analyzing positive samples.

Florida and Michigan lead the country in these raw numbers. Michigan Gov. Gretchen Whitmer told CNN Wednesday that one of the reasons for the state’s surge is that “we’ve got a high proportion of variants, and that means coronavirus spreads faster.”

Overall, a majority of states are seeing cases rise from week to week, according to data from Johns Hopkins University. Cases in Michigan are up more than 50%, and cases in Florida are up 12%.