Chris Martin of Lewiston sits on a park bench Thursday in Lewiston. He feels people should wear masks indoors to do their part to stop the spread of the virus. Andree Kehn/Sun Journal

LEWISTON — New information from the U.S. Centers for Disease Control and Prevention on the delta variant appears to offer some explanation for rising case rates and for the sudden shift in prevention recommendations announced earlier this week, which say that all people — vaccinated or not — should wear a mask indoors in some instances.

Maine followed suit Wednesday and said it would follow the U.S. CDC’s guidance that individuals in counties with high levels of transmission should take extra steps to protect themselves. The delta variant, Maine CDC Director Dr. Nirav Shah said at a briefing, is to blame for this shift.

“Based on what we know today, the delta variant is more wily and more formidable.”

It has “become far more prominent in Maine,” accounting for at least 50% of new cases but likely more, Shah said.

State health officials reported 111 new cases of COVID-19 in Maine on Friday, including four each in Androscoggin, Franklin and Oxford counties.

As of Friday, there was an average of 0.58 new cases per 10,000 individuals over the past week across the state. In Androscoggin, Franklin and Oxford counties, the seven-day average per 10,000 individuals was 0.25, 0.38 and 0.5, respectively.

Except for Androscoggin County, those numbers were greater than where they stood last Friday.

“On top of all this, in rare situations, even people who are fully vaccinated can transmit COVID-19 to other people,” Shah said.

The shift in recommendation caused confusion and frustration. Not only do the county-level transmission designations change daily, but some have expressed that unvaccinated people got Maine in this situation, while others have cast doubt on the vaccines’ efficacy.

But internal documents from the U.S. CDC, published by The Washington Post Thursday night, suggested that the delta variant could spread as easily in fully vaccinated individuals as it does in unvaccinated individuals.

This echoes what Shah said Wednesday: Masking up indoors lowers “the risk that you could unknowingly, inadvertently spread the virus to someone, even though you yourself are fully vaccinated.”

He cited a rise in so-called “breakthrough” cases in Maine and nationwide, which occurs when an individual fully inoculated against COVID-19 contracts the disease.

As of Friday, there were 656 breakthrough cases in Maine.

“This is a rare phenomenon,” Shah said. The cases represent less than 0.1% of fully vaccinated Mainers who have contracted COVID-19, and the breakthrough cases represent about 0.9% of Maine’s cumulative case count.

Ninety-six more vaccinated people had confirmed cases of COVID-19 than the week ending July 16. As of the same date, 27 of the breakthrough cases resulted in hospitalizations and 13 in death, according to the Maine CDC.

“Most of the deaths were among people receiving end-of-life care or who had other significant medical problems,” Maine CDC spokesperson Robert Long said in an email.

“Most of the spread that’s happening around the country is among unvaccinated individuals and in areas of low vaccination rates,” Shah said. “Simply put, vaccines remain the best tool we have to keep ourselves safe. They continue to work, and they continue to work well.”

While Maine has one of the best vaccination rates in the country, pockets of unvaccinated people remain.

About 68% of all eligible Mainers are fully inoculated. In central and western Maine, Androscoggin County has the highest vaccination rate, with about 61% of residents 12 years and older fully vaccinated. Eligible residents in Franklin and Oxford counties were 57% and 58% fully vaccinated, respectively.

Farmington in Franklin County, and Auburn, Lewiston and Sabattus in Androscoggin County remain the remaining holdouts in the tri-county area, where more than 2,000 residents remain unvaccinated, according to the Maine CDC’s July 26 update to ZIP code-level vaccination rates.

The concern, and reason for the change in masking recommendations, is because a vaccinated person could unknowingly spread the disease to an unvaccinated person, Shah said.

The U.S. CDC documents indicated that the delta variant may also be more likely to cause severe illness.

Mid-July, the same time that case counts began to increase, Central Maine Medical Center started to see an increase to their average daily in-patient counts.

A representative of the Lewiston hospital was not available for comment Friday.

On July 11, providers at CMMC were caring for an average of 1.14 patients with confirmed COVID-19 over the previous seven days. On Friday, that number increased to five.

Hospitalization rates at the hospital are still nowhere near where they were during the spring surge. But hospitalizations being a lagging indicator of case trends, the numbers over the next few weeks will be reflective of community-level transmission right now.