At the end of May, 40 percent of the new COVID-19 cases in Colorado were associated with the more transmissible and dangerous strain known as the Delta variant — one of the highest rates in the country.

And the situation has gone from bad to worse. The Colorado Department of Public Health and Environment just released data for the first two weeks of June indicating that the percentage of Delta variant cases has grown in a major way. The strain, technically known as B.1.617.2, accounted for 55.74 percent of new COVID-19 cases in Colorado for the week ending June 6, and a staggering 75 percent for the week ending June 13.

Variant case percentages are based on what the CDPHE describes as "a small sampling of positive COVID-19 tests" and don't account for all new infections in the state. However, the agency is tracking confirmed Delta variant cases in all 64 Colorado counties, and figures shared on June 23 reveal that the strain has now appeared in 23 of them, including most metro Denver counties.

While the number of confirmed Delta variant cases in many of these counties looks small, the department believes there are many more, increasing the risk of greater transmission — particularly in places with low vaccination rates, as calculated on the CDPHE's vaccine data dashboard. Of the counties where the Delta variant is spreading, eight are below 50 percent, including Mesa, one of the CDC's national poster children for low inoculation rates, with just 44.5 percent of its eligible residents vaccinated.

Mesa County has far and away the most confirmed Delta variant cases in Colorado: 288, up 40 from the total on June 22. In the county with the second-highest number of Delta variant cases, El Paso County, with 103, just 50.2 percent of eligible residents have at least started the immunization process.

Here are the current number of Delta variant cases in the 23 counties where it's been identified, along with the updated vaccination rates for each.

Bent County — 1
Vaccination level: 20.5 percent

Pitkin County — 1
Vaccination level: 82 percent

Rio Blanco County — 1
Vaccination level: 35.8 percent

Routt County — 1
Vaccination level: 74.2 percent

Saguache County — 1
Vaccination level: 35.4 percent

Sedgwick County — 1
Vaccination level: 47.3 percent

Teller County — 1
Vaccination level: 51.1 percent

Jefferson County — 2
Vaccination level: 74.2 percent

Larimer County — 2
Vaccination level: 64.6 percent

Las Animas County — 2
Vaccination level: 58.2 percent

Fremont County — 3
Vaccination level: 37 percent

Montrose County — 3
Vaccination level: 44.5 percent

San Miguel County — 3
Vaccination level: 84.9 percent

Weld County — 6
Vaccination level: 57.3 percent

Denver County — 6
Vaccination level: 71.8 percent

Adams County — 10
Vaccination level: 62.1 percent

Arapahoe County — 12
Vaccination level: 63.1 percent

Boulder County — 12
Vaccination level: 75.3 percent

Moffat County — 18
Vaccination level: 37.5 percent

Douglas County — 20
Vaccination level: 68.4 percent

Garfield County — 27
Vaccination level: 60.1 percent

El Paso County — 103
Vaccination level: 50.2 percent

Mesa County — 288
Vaccination level: 44.5 percent