Breakthrough cases are on the rise in La Plata and Archuleta counties.

Vaccinated people increasingly account for new COVID-19 cases as the highly transmissible omicron variant spreads across the two-county area. Public health officials say it is unclear whether boosted or twice-vaccinated individuals are driving the uptick.

“We do observe breakthrough cases not only in fully vaccinated individuals, but also in people who are boosted,” said Chandler Griffin, spokesman for San Juan Basin Public Health. “These vaccines, their primary purpose is preventing severe illness, hospitalization and death.”

In November 2021, the fully vaccinated made up 28.5% of new cases in La Plata and Archuleta counties, according to SJBPH data. A month later, that figure jumped to 37.8%.

COVID-19 cases are now roughly split between those who are vaccinated and unvaccinated, with fully vaccinated people totaling 46.9% of cases.

The Centers for Disease Control and Prevention defines full vaccination as those who are two weeks removed from two shots of the Moderna or Pfizer vaccine or two weeks removed from the Johnson & Johnson shot.

Breakthrough cases are higher in La Plata County than Archuleta County.

Of the 2,932 COVID-19 cases in La Plata County in the last 30 days, 1,400, or about 48%, have been breakthrough cases.

In Archuleta County, only 38% of cases were reported as breakthroughs.

Liane Jollon, executive director of SJBPH, said the difference comes down to math.

“Any place that you have a larger percentage of the population vaccinated, you’re going to see more breakthroughs,” she said.

La Plata County has a slightly higher percentage of fully vaccinated residents with 66% of its population compared with Archuleta’s 59%.

While local public health officials are following breakthroughs, the data does not differentiate between those who are fully vaccinated and boosted.

“Public health continues to track breakthroughs based on whether someone has completed their initial vaccine series,” Griffin said. “There’s not robust tracking of breakthroughs for people who have had boosters or not had boosters.”

According to the Colorado Department of Public Health and Environment, those who are fully vaccinated are two times less likely to become infected with COVID-19.

As of Jan. 2, the state was seeing about 550 cases per 100,000 people in vaccinated individuals and nearly 1,075 cases per 100,000 people in those who remain unvaccinated, according to CDPHE data.

A study by Danish scientists from the University of Copenhagen, Statistics Denmark and Statens Serum Institute released on Dec. 22 found that the omicron variant is 2.7 to 3.7 times more infectious than the delta variant for those who are vaccinated.

Other research has similarly shown that vaccines do not offer the same protection from infection with the omicron variant.

A study by scientists in South Africa, which was the first country to be hit by an omicron surge, showed that effectiveness of the Pfizer vaccine against infection decreased from 80% to 30% for omicron.

In Israel, a fourth shot did not protect people from the new variant, according to a preliminary study by researchers at Sheba Medical Center.

“The transmissibility piece is definitely more complicated than the prevention of severe illness piece,” Griffin said.

Public health officials with SJBPH have no expectation for how many breakthrough cases will happen in La Plata and Archuleta counties. The speed with which omicron has spread has left them without much data and research to work from, Jollon said.

“(Omicron) was identified in November, it was labeled a variant of concern the last week in November, and it took the us by storm the latter half of December and the beginning of January,” she said. “I don’t think that was (enough) time for public health professionals to have a good handle on what we would expect in any of our local communities with breakthrough cases.”

While breakthroughs climb, data suggests that COVID-19 vaccines still protect against severe disease and death.

Coloradans who are fully vaccinated are 11.8 times less likely to be hospitalized with COVID-19 and 12.9 times less likely to die, according to CDPHE.

The same study in South Africa that found a drop in the Pfizer vaccine’s effectiveness against infection indicated that two shots still offered about 70% protection against hospitalization.

“Locally and nationally, the data does reflect that the vaccines continue to be effective against omicron in preventing severe illness and hospitalization, even though we are seeing more breakthroughs than we did previously,” Griffin said.

SJBPH released data on Tuesday showing a decline in COVID-19 cases in recent days. While the trend is a positive development, Jollon said the state currently lags sending data to counties and people tend to test less over holiday weekends.

“We have noted that these numbers have dropped over the last few days, but until the state has a chance to fully catch up on the data that’s due to counties and we have a few more days of testing, it’s definitely too soon to celebrate,” she said.

ahannon@durangoherald.com