AUGUSTA — The Maine Center for Disease Control and Prevention said July 31 that an additional 91 cases of COVID-19 were reported statewide in the past day, including one additional death — a Waldo County man in his 50s. His passing increases the statewide death toll to 900. With risk rising, masks are recommended indoors.

Forty-three new cases were reported in Waldo County in the seven days prior to July 31, six of them July 30. By July 31, eight more people had been hospitalized statewide, increasing that total to 2,149 since the pandemic began. Forty-one people were in hospitals across the state, with 16 in critical care units and nine on ventilators.

The Maine counties of Waldo and Somerset had high enough COVID-19 transmission rates as of July 31 to trigger state and federal recommendations that people wear masks in indoor public settings regardless of their vaccination status. Somerset County’s rate of community transmission is now classified as “substantial,” while Waldo County’s is “high,” an increase in severity from its “substantial” rating the previous day.

As of Wednesday morning, Aug. 4, Waldo County’s rate of community transmission remains high. On Aug. 2, there were 17 confirmed and 12 probable new cases, according to Maine CDC, with another 10 confirmed and five probable new cases Aug. 3.

Statewide, Maine CDC reported 111 new COVID-19 cases July 30, marking the second straight day with a triple-digit increase. The seven-day average of new cases in Maine stood at 78 July 30, compared to 59 for the week ending July 23 and nearly quadruple the average at the beginning of the month.

The Maine CDC also released new data showing that 656 vaccinated individuals have tested positive for COVID-19 since monitoring began. That’s an increase of 60 “breakthrough cases” since the previous week.

While vaccinated individuals can still contract and spread the coronavirus — particularly the new delta variant — they are significantly less likely than the unvaccinated to develop severe cases requiring hospitalization or leading to death.

Unvaccinated people, who account for the vast majority of severe cases and deaths, are recommended to mask in public settings regardless of the local transmission rate. Because Maine’s civil state of emergency expired at the end of June, state health officials can no longer mandate mask-wearing.

In Waldo County, 57.5% of residents are fully vaccinated, the CDC reported July 31, and 61.7% have had at least one dose. Health officials say that the rapid spread of the delta variant is being worsened by the failure of more people to be vaccinated.

In an appearance Aug. 1 on CBS’s “Face the Nation,” Anthony Fauci, the president’s chief medical adviser, said CDC data show levels of coronavirus in breakthrough cases of the delta variant among the fully vaccinated are “almost identical” to levels seen among unvaccinated individuals, which means “vaccinated people who get breakthrough infections can spread the virus to other people.” Fauci also said the majority of breakthrough cases involving the delta variant saw “minimal symptoms or no symptoms at all.”

Addressing the situation in Maine, a public health expert interviewed last week in The Portland Press Herald cautioned that because of how the federal government calculates transmission rates, even small changes in the number of COVID-19 cases will cause significant shifts in whether some counties are classified as “low” or “high” transmission rates.

“They use some excellent methodology except that it is really geared toward urban areas and not rural areas,” Dr. Dora Anne Mills told Press Herald staff writer Kevin Miller. She is chief health improvement officer at MaineHealth, a former director of the Maine Center for Disease Control and Prevention, and the sister of Gov. Janet Mills.

Beyond Waldo and Somerset, the other 14 counties in Maine are designated as having “moderate” levels of transmission. But Mills noted that COVID-19 incidence rates and positive test rates are headed upward in all 16 counties at a time when the more transmissible delta variant is causing more infections, hospitalizations and deaths nationwide.

“We are in a very different chapter of this pandemic,” Mills said.

The delta variant, which was first detected in India but has since swept around the world, is at the root of the current surge in the United States and other countries. Research suggests that the variant is at least twice as contagious as the previous dominant strain and that it may lead to more severe illness.

In her Press Herald interview, Mills said it is important to put the rising number of breakthrough cases in Maine and nationwide into context. Roughly 60% of the total population of Maine — and nearly 70% of those eligible — are vaccinated against COVID-19 right now, while the vast majority of new infections are occurring among unvaccinated people.

Putting it in mathematical terms, Mills said the “denominator” of vaccinated people is much larger in Maine. “So even a small percentage of that is going to be a larger number because you have a larger denominator,” she said.