Pigeons take to the air from a sign at the Auburn Mall where a COVID-19 mass vaccination clinic opened on Wednesday, March 17, 2021, in Auburn, Maine. Credit: Robert F. Bukaty / AP

AUGUSTA, Maine — Vaccinations and natural immunity are likely driving down coronavirus cases in Maine, the state’s top health official said Thursday, but concerns remain as variants continue to spread and infections remain high in pockets of western Maine.

The seven-day average of new cases in Maine has declined 28 percent over the past two weeks after climbing for much of March and early April. But hospitalizations, which are often a lagging indicator, have yet to show a similar decline, with 125 people still hospitalized with the virus. Maine reported four additional virus deaths on Thursday, including a person in their 20s.

Increasing rates of immunity from vaccinations as well as in people who have already had the virus likely played a role in the declining cases, said Nirav Shah, director of the Maine Center for Disease Control and Prevention, during a Thursday news conference. Just over half of Mainers have received at least one vaccine dose as of Thursday, according to state data.

Shah said adherence to public health guidelines could also be helping bring cases down. But he cautioned the spread of more contagious variants could still allow the virus to spread here even as Maine continues its vaccination effort. Vaccines have been shown to protect against the known variants of the virus, but they can still spread among unvaccinated people.

“We see those positive signs from immunity, behavior, perhaps seasonal changes. Those are helping keep cases down, but variants that we’ve detected are helping keep it up, unfortunately,” Shah said.

Although cases have declined throughout the state, they remain higher in western Maine. The seven-day case rate in Androscoggin County is more than double the state’s overall rate, driven by infections in Lewiston and Auburn but also in smaller towns. Mechanic Falls, a town of about 3,000 people, saw 61 cases in the past two weeks, the highest rate of any zip code in Maine during that period.

Shah said Androscoggin County remained “concerning,” noting the region was also seeing a higher positivity rate than the rest of Maine. He said the state was working with vaccine sites, including the mass vaccination site at the Auburn Mall as well as local pharmacies, to increase a vaccination rate that has lagged other parts of the state so far.

Just 53 percent of adults there have received at least one dose of any vaccine, according to state data. Only four other counties — Oxford, Somerset, Franklin and Piscataquis — have lower vaccination rates than Androscoggin. Oxford and Somerset counties also have the second- and third-highest infection rates over the past week.

Between 75 percent and 85 percent of Mainers will likely need to get vaccinated to achieve herd immunity, Shah said. Current vaccination rates vary widely by geography as well as age groups, with just shy of 41 percent of Mainers between the ages of 16 and 39 having received at least one dose of the vaccine, according to data from the Maine CDC, compared to 70 percent of people aged 40 and older.

Shah advised younger Mainers to get vaccinated as soon as possible, noting that several mass vaccination sites including the Portland Expo now offer vaccines to walk-ins. Although older Mainers still make up the majority of COVID-19 hospitalizations, the deaths of younger Mainers in the past few weeks are a reminder that the virus can affect anyone, Shah said.

“As the virus circulates, more younger people will get infected. A subset of them, sadly, will be hospitalized, and a subset of those who are hospitalized unfortunately will die,” he said. “That is, sadly, what we are seeing.”