In a significant shift, Island boards of health have issued a mask advisory for indoor public spaces on the Vineyard, regardless of vaccination status, as case numbers rise and the contagious Delta variant continues to spread on the Island.

The indoor mask advisory was issued in a press release from Tisbury health agent Maura Valley Wednesday afternoon, and follows new guidance from the Centers for Disease Control that masks should be worn in crowded indoor spaces.

“In accordance with the most recent CDC guidance and the fact that Dukes County is considered to be at substantial risk for COVID transmission, the Island boards of health strongly advise that individuals wear masks when indoors or in enclosed spaces serving the public or when unable to maintain social distance, regardless of vaccination status,” the release said.

Speaking to the Gazette by phone, Ms. Valley said the recommendation from the boards of health is just that: a recommendation.

“Really, it’s an advisory,” Ms. Valley said. “We’re basically strongly recommending, but it’s stopped short of a mandate.”

The announcement comes after health agents have reported more than 20 new Covid-19 cases in the past two weeks, with at least 12 of them breakthrough cases among fully-vaccinated individuals.

After sending test samples to the state epidemiology lab for sequencing, the Delta variant has also been identified in at least four positive Covid-19 individuals on the Island. According to the Island health agents, the variant is far more transmissible and leads to an infection and symptoms much more quickly than the original virus.

In the release, health agents said that although fully-vaccinated individuals are at a much lower risk of infection, illness, hospitalization and even death, they can still be infected and not know it, as well as transmit the virus.

Ms. Valley said that while the advisory could apply to restaurants and public office spaces, the guidance was focused mainly on indoor retail spaces, particularly in crowded downtown and Main street business districts on the Island.

“It’s more for stores,” Ms. Valley said. “You walk into stores, and you see a lot of customers and staff walking around without masks. We’re saying, with the Delta variant, and the uptick in cases, we’re strongly advising that you wear a mask.”

She emphasized that the guidance was for public, rather than private, indoor spaces.

“We’re not saying wear masks when you’re in your house,” Ms. Valley added.

According to Ms. Valley, Provincetown, which has seen case numbers balloon to more than 800 after a cluster was identified in the town last weekend, is currently the only municipality in the state with a mask mandate.

The press release also included five pieces of advice for Islanders based on CDC guidance and current public health standards, which follow:

• Please get vaccinated.

• Give careful thought to entering crowded indoor space if an alternate time might be less crowded.

• Enjoy as many of your activities as you can outdoors and ventilate indoor space shared with non-household members as much as possible.

• Get tested If you believe you’ve been exposed and stay home if you are not feeling well.

• If you are fully vaccinated, consider not mixing with un-vaccinated friends or family indoors.