A new coronavirus subvariant is now dominant in Colorado, the latest strain to hold the throne here amid months of rivalries and emergences. It’s mild, transmissible — just as transmissible as its omicron siblings — and may be better at escaping previous immunities.

BA.5, as this strain is known, first became dominant a full month ago, state data shows. But, so far, Colorado’s reported COVID-19 numbers have remained in a plateau: Hospitalizations are stable and low, the positivity rate is high but declining, and case counts have actually improved in recent weeks.

That’s “surprising,” said Jon Samet, the dean of the Colorado School of Public Health, as the “expectation would be a rise and a fall — not a plateau.” His team’s ongoing projections, he continued, indicate that a further decline may be coming, even as cases rise elsewhere globally because of BA.5.

Part of the explanation may be that Colorado has high levels of vaccination and prior infection, even with BA.5’s ability to evade immunity. Beth Carlton, an epidemiologist with the public health school, said Colorado had a lot of infections from a previously dominant variant — BA.5’s sister, BA.2.12.1 — and that may help protect the state.

Testing may also be an explanation: The state has shuttered many of its community test sites, and take-home tests are more available now than during previous waves. More people may be testing positive at home and not reporting, meaning the state’s data system isn’t capturing them, officials said. Indeed, state data shows public testing remains low compared to previous points of the pandemic.

Carlton said the number of infections in Colorado may be comparable to those seen during parts of the initial omicron surge, when infections reached unprecedented highs in December and January. But hospitalizations are lower, she continued, because the strain is mild, vaccinations are widespread, medications to treat the virus are more available, and enough Coloradans have been infected before to confer further immunity.

She said while tracking case counts is important, they’re reliant on people actually seeking testing at public sites.

For her part, Carlton says she’s optimistic — “but not very confident” — the state is “going to see infections and hospital demand decline over the next few weeks.”

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