A tester holds printed instructions at a mobile testing location for COVID-19, Tuesday, Dec. 8, 2020, in Auburn. Credit: Robert F. Bukaty / AP

AUGUSTA, Maine — Maine continues to see lower COVID-19 cases as the more contagious delta variant drives sharp increases across the U.S., but health experts warn of a threat to the state’s unvaccinated population as the variant spreads more here.

Coronavirus cases are up 94 percent over the past two weeks nationwide, according to the New York Times. Health officials have attributed much of the national rise to the delta variant, with the U.S. Centers for Disease Control and Prevention concluding last week that the new strain is now responsible for more than half of new virus cases nationally.

Trends in Maine have been the opposite, with coronavirus infections declining steadily for the past three months. The seven-day average of new cases here was just 28 as of Tuesday, down 45 percent from a month earlier, with health officials pointing to high vaccination rates as the primary reason. But that may not be enough to ward off the more contagious strain.

“While Maine’s high vaccination rate limits routes of transmission, the delta variant is opportunistic,” Nirav Shah, the director of the Maine Center for Disease Control and Prevention, said.

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The Maine CDC “expects to see a greater impact of the delta variant in the state in the coming weeks,” Shah said. At the same time, limited testing makes it difficult to assess to what extent the delta variant has already spread in Maine.

The delta strain accounted for only 34 percent of virus cases in New England compared to 51 percent nationwide in the latest U.S. CDC estimates, One analysis identified eight “clusters” of the delta variant scattered across eight states with low vaccination rates, none of which are near Maine.

The state has recorded only five cases of the delta variant so far, but officials acknowledge that is an undercount. The number of cases undergoing genomic testing here has dropped in the past month, coinciding with an overall decline in infections. Maine has evaluated 68 samples from June compared to 783 in the month of May, though more June samples are still expected to be tested.

Recent tests by MaineHealth, the state’s largest hospital system, found 18 cases of the delta variant when samples from 49 testing patients using a rapid testing device. Maine CDC spokesperson Robert Long said the agency was analyzing some of the MaineHealth samples but cautioned that the hospital system’s tests are not as accurate as full genomic sequencing because they look for genetic markers that may also show up in other variants.

Patterns in other states suggest that it is only a matter of time until the delta variant becomes the predominant strain in Maine as well with a handful of cases confirmed and no travel restrictions in place, said Dr. Peter Millard, a Belfast physician and former U.S. CDC staffer.

He identified particular concern about regions of the state with lower vaccination rates. Research suggests the vaccines still work well against the delta variant, but rates vary widely in Maine, from more than 70 percent in Cumberland County to just 47 percent in Somerset County.

“It’s not going to be a problem in places that are highly vaccinated like Portland, or even Belfast or Bangor,” Millard said. “There will be sporadic cases, but there are probably going to be legitimate outbreaks in the more rural areas with lower vaccination rates.”

Shah noted that vaccinations remain the best way for Mainers to protect themselves against the variant. The state has maintained vaccine clinics across the state and announced a new clinic at the Portland International Jetport on Tuesday, though demand for new vaccines has decreased significantly over the past few months.

In the long-term, unvaccinated people remain at risk for contracting the virus, whether it is from the delta variant or a future variant yet to be detected, Millard said, as it is likely to continue circulating.

“It’s not going away,” he said. “It’s going to be here next year and the year after, so if people don’t get vaccinated and it doesn’t get them this year, it will eventually. Or another variant and that’s going to come along.”