Even as Colorado's COVID-19 restrictions loosened in the past couple of months, the state continued to enjoy falling rates of new coronavirus cases — but Coloradans risk reversing that trajectory if they start to have more face-to-face contacts than they do now.

“If Colorado remains on the current trajectory, statewide hospital demand and cases will continue to decline,” a Feb. 24 report by the Colorado School of Public Health says.

Optimistically, the report adds: “It will be over a month before hospital demand and infection prevalence reach (the low) levels comparable to last summer.”

The state may be on a riskier track, though, if Coloradans start to have more in-person contacts and let their guard down on behaviors such as mask-wearing.

A key indicator to watch is the “effective reproduction number,” sometimes written “Re,” a measure of how rapidly COVID-19 infections are spreading. It's a similar measure to Colorado's R0 — pronounced “R-naught” — that state officials discussed in the pandemic's earlier stages.

The reproduction number shows how many people each infected person will, on average, likely spread the virus to. If the number sits below 1, infections are decreasing.

Colorado's most recent estimate is 0.95, reflecting the virus's spread in early February. That means the rate of new cases could soon start to increase again if the public isn't cautious.

Coloradans appeared to be having more in-person contacts in early February compared to in January, according to the report. On top of that, if the more-contagious COVID-19 variant from the United Kingdom spreads rapidly in Colorado, the state could see another peak in hospital demand, the report says.

As of late February, Colorado is not seeing rapid spread of concerning variants, according to the state public-health department. But the UK variant could begin to take firmer hold by mid-March, the report says.

Those developments come as more counties close to Denver — including Jefferson, Park, Clear Creek and Broomfield — recently entered level blue on Colorado's color-coded “dial” of restrictions, further loosening rules for restaurants and other businesses.

Blue could soon spread

Level blue, the next-lowest notch on the dial since the Denver metro area entered level yellow on Feb. 6, appears to be a possibility for more metro counties in the next several weeks.

The state's COVID-19 dial is the set of restrictions counties must follow based on local virus spread. Counties now land in level blue when they drop below 100 new COVID-19 cases per 100,000 people within one week, a measure known as a county's incidence rate.

As of Feb. 25, Adams County sat at 129, Arapahoe at 115, Douglas at 136, Denver at 112 and Weld at 137. Elbert County appeared poised to possibly move into level blue the soonest, with a rate of 75.

The level a county qualifies for generally also depends on the county's percentage of COVID-19 tests that come back positive and whether hospitalizations are increasing, stable or declining. To move to a lower level, a county must meet the criteria for all three metrics.

Hospitalizations are considered on a regional basis, so if hospitalizations are stable or declining regionally, counties still can move to a different level, according to a statement from the Colorado State Joint Information Center. That's the office that takes questions for the state public-health department.

The state moved Broomfield to level blue effective Feb. 22, according to Broomfield's website. Jefferson, Park and Clear Creek counties entered level blue on Feb. 26, according to the state's COVID-19 website.

In level blue, restaurants indoors are allowed up to 50% capacity or 175 people (or up to 225 using the state's social distancing space calculator), whichever is fewer. That's up from 50% capacity or 50 people (or up to 150 using the calculator), whichever is fewer, in level yellow. Other businesses see capacity expand as well. See the calculator here.

See a full list of which restrictions apply to which levels on the dial in the full policy explainer on page 6.

Changing standards

The dial changed with the addition of a new level red that took effect Nov. 20 in metro Denver and other areas of the state, banning private gatherings and indoor dining at restaurants and tightening capacity limits at some types of businesses. Red is the second-highest level next to purple, a stay-at-home order. Eventually, more than half the state's 64 counties operated in level red.

Citing improving virus trends, Gov. Jared Polis on Dec. 30 announced that he told the state public-health department to move counties from red to orange effective Jan. 4 — even though many didn't meet requirements for level orange according to the dial system.

Under the “dial 2.0” changes to Colorado's COVID-19 restrictions on Feb. 6, the state public-health department drastically eased the incidence-rate limits that allow counties to remain in certain levels of the dial. The “dial 2.0” system put Denver metro counties in level yellow.

Businesses have had their eye on another wrinkle: Colorado's 5-Star State Certification Program, which allows businesses to operate with expanded capacity if they follow stepped-up COVID-19 safety protocols. The program lets businesses follow restrictions that are one level lower on the dial than they otherwise would be able to without certification.

But the state on Feb. 5 said businesses in level-yellow counties with 5-Star certification programs could only operate at blue restrictions once 70% of 70-year-olds in the state are vaccinated with at least one dose, which was expected to happen by the end of February, according to a state public-health department news release.

On Feb. 26, Polis announced that Colorado will have vaccinated 70% of the state's 70-and-over population likely by the end of the Feb. 27-28 weekend, according to an Arapahoe County news release.

The 5-Star program may soon be entirely irrelevant in more metro counties as they move to level blue — unless worsening virus trends cause a county to move back up to tighter levels. That's because businesses with 5-Star certification may not operate in the next-lowest level below blue — level green, or "Protect Our Neighbors" — unless the county is formally in that level.

Level green, the lowest level on the dial, is more difficult to transition to than others. Counties must apply for that level based on criteria including hospital bed capacity, supply of personal protective equipment, hospitalizations, COVID-19 testing capacity, contact-tracing ability and other requirements.

State 'could see another peak'

Whether the Denver metro area can remain on track with decreasing virus numbers as some counties open up further is unclear.

“There is considerable uncertainty about how policies and behaviors over the last few weeks will influence the course of the epidemic, how rapidly the B.1.1.7 (UK variant) will spread in Colorado, and how rapidly the vaccine will be administered,” the Colorado School of Public Health's report says.

As of Feb. 25, the state's trend of new cases per day appears as if it may be flattening after several weeks of mostly steady decline. The school of public health's estimate of daily infections appears to show a flattening in recent weeks.

Meanwhile, after several weeks of general decline in the number of daily deaths among people with COVID-19, the number of deaths stayed flat in late January and showed a small uptick at the end of that month.

“If the B.1.1.7 variant spreads rapidly in Colorado and (in-person contacts increase) over the short term, we could see another peak in hospital demand,” the report says. If contacts increase drastically enough and Colorado sees rapid spread of the variant, demand could exceed intensive care unit capacity and approach hospital capacity, according to the report.

If trends take a turn for the worse, it is too early in Colorado's vaccination distribution to create enough community protection to prevent another spike in cases and deaths, the State Joint Information Center said.

Asked if the state public-health department anticipates counties needing to be moved back to level yellow, orange or even red when spring weather and Memorial Day cause people to gather more, the center said it's unclear.

“We are encouraged by the recent data, but it's too early to tell what disease transmission will look like in the spring,” the center said.