While COVID-19 transmission rates in Androscoggin, Franklin and Oxford counties remained below the threshold at which masks are recommended for all people, all but one neighboring county recorded substantial levels of community spread Wednesday.

State health officials reported four new cases of COVID-19 in Androscoggin County on Wednesday and three each in Franklin and Oxford counties. A total of 126 new cases were reported across the state and there were no additional deaths.

Cumberland, Kennebec, Somerset and York counties all had substantial rates of community transmission. Sagadahoc County was the only neighboring county that had a low transmission rate.

Maine adopted the U.S. Centers for Disease Control and Prevention’s guidance last week that said universal masking indoors is recommended in areas of substantial or high transmission rates.

The best way to cut off community transmission is through vaccinations, public health experts have said.

In Androscoggin, Franklin and Oxford counties, the seven-day average of new daily cases per capita Wednesday was higher than one week ago and one month ago. It was the same for the average statewide.

Joanne Kenny-Lynch, system director of infection prevention at Central Maine Healthcare, said earlier this week that higher vaccination rates mean the virus has less opportunity to mutate.

“Viruses have one goal, and that’s really to survive,” she said. “And the more of a chance that we give the virus to replicate in our communities and our environment, the higher chance we have for seeing different mutations or different variants.”

Just short of 70% of all eligible Mainers are fully vaccinated against COVID-19. In Androscoggin, Franklin and Oxford counties, the vaccination rate among eligible residents ranged from 58% to 62%.

The delta variant is more contagious than the original strain of the COVID-19 virus, but Kenny-Lynch warned that “the next variant may be more resistant to vaccines, or it may cause a different issue.”

CDC officials have said available vaccines are highly effective at preventing infection, including against the delta variant. Even in rare “breakthrough cases,” vaccinated people rarely experience severe illness requiring hospitalization or die from the disease.

In Maine, the majority of vaccinated people who were hospitalized or died due to COVID-19 — a small fraction out of the total vaccinated in the state — had preexisting conditions or were receiving end-of-life care, a spokesperson from the Maine CDC said last week.

“The big piece is to get the vaccinations to get the number of people who are infected in our communities down and stop of the mutation of this virus,” Kenny-Lynch said.

“I’m not sure that everyone has that full concept that, yes, we need to protect ourselves and protect everybody else,” she said. “But if this thing keeps spreading around, we’re going to see some really funky other variants potentially come out.”

Community transmission rates are a way to “forecast” where the virus is spreading, Dr. Dora Anne Mills, MaineHealth’s chief health improvement officer, said in an interview Tuesday.

The U.S. CDC uses two metrics to determine if a county has low, moderate, substantial or high levels of community transmission: The total number of new cases per 100,000 people over the past seven days and the testing positivity rate.

Mills said that in rural areas, the denominator, which is the total population, “is statistically small enough that even small variations in the disease,” such as a few new cases, could “cause that county to flip from low to high.”

Maine CDC Director Dr. Nirav Shah called the situation in Maine “the law of small numbers,” during a Monday broadcast of “Maine Calling” on Maine Public.

He said he recognizes that this system “whipsaws” people and it’s “not easy to follow up” with the daily changes.

“We’re taking a look now that we’ve gotten five days of experience with the way the U.S. CDC tracks these things,” he said. “We’re taking a look to see whether that’s the exact right approach for Maine.”

Still, Mills said the methodology is “excellent,” and with the spread of the delta variant, “it’s better to err on the side of caution and have the system be more reactive.”

She compared it to checking the weather forecast for chance of rain, “where you look at the weather forecast in the morning and decide whether you’re going to wear a raincoat and take an umbrella with you,” Mills said, who served as the Maine CDC director for over 14 years.

The vaccine, like a raincoat, is the first level of protection. “Then, masking, distancing, ventilation” — like an umbrella, rain boots and other water-resistant gear — those are the “three other major layers of protection.”