The Perfect Enemy | CDC: Only 1 Mass. county now has a high community level of COVID-19

Only one Massachusetts county, Hampden, currently has a high level of COVID-19, according to the US Centers for Disease Control and Prevention. That number is down from as high as 11 last month.

Hampshire County and Dukes County, which comprises Martha’s Vineyard and some smaller islands, have medium levels. The rest of the state’s 14 counties were rated as having low levels, the CDC said Friday.

The CDC calculates community COVID-19 levels each week by reviewing the number of hospital beds being used, hospital admissions, and new COVID-19 cases in an area.

Statewide, reported case numbers have been trending down since mid-May, and hospitalizations have been dropping since about a week after that, according to data released by the state Friday.

CDC recommends that people wear masks in indoor public spaces, including schools, regardless of vaccination status, when communities have a high COVID-19 level, as Hampden County has. (The agency notes that people can wear masks at any level based on personal preference.)

The CDC recommends an increasing number of precautions, depending on how high the COVID-19 community level is, beginning with basics such as getting vaccinated and staying up to date on boosters, improving ventilation, and getting tested if you’ve been exposed to COVID-19 or have virus symptoms.

Pandemic models had suggested that the most recent wave of COVID-19 infections in the state, which had been gradually rising since March, would begin losing steam in May. Experts said they thought that would happen for a variety of reasons, including the immune protection people had gotten from vaccinations and previous infections, and the arrival of warmer weather.

A note of uncertainty about the pandemic trajectory has been injected by the arrival of two new Omicron subvariants, BA.4 and BA.5. Experts said recently it was possible the new subvariants could push case counts up again.

Material from prior Globe stories was used in this report.

Martin Finucane can be reached at martin.finucane@globe.com.