After weeks of decline, Covid-19 cases shot up again on Martha’s Vineyard, with health agents reporting 16 new cases last week, including six breakthrough cases among vaccinated residents.

In a weekly case update, Island boards of health reported 11 symptomatic, one asymptomatic and four unknown cases between July 11 and July 17. The 16 new cases come after six straight weeks in which health agents reported four cases or fewer, with cases in late June dropping to zero on the Island.

According to the update, all but one of the cases were tested at the Martha’s Vineyard Hospital. While six of the new cases are among unvaccinated residents, four are unknown and six are among fully vaccinated residents. Monday’s update marks the first time health agents have specified the vaccination status of patients.

Ten of the cases are currently active, health agents reported, with cases in every age group from zero to 70. Four of the cases are among patients over the age of 70.

In an interview with the Gazette Monday morning, Tisbury health agent Maura Valley said that the patients were generally experiencing mild symptoms.

“The people that we reported this week, I don’t believe any of them were extremely ill,” Ms. Valley said. “I think the symptomatic individuals were mildly symptomatic. I have not heard of any of the vaccinated individuals this week being extremely ill.”

According to the Centers for Disease Control, both the Pfizer and Moderna two-shot, mRNA Covid-19 vaccines have been shown to reduce the risk of Covid-19, including severe illness, by 90 per cent or more among people who are fully vaccinated. While breakthrough infections can occur among vaccinated people, data has shown infections to be less severe, according to the CDC.

Approximately 86 per cent of Dukes County has received two vaccine shots, according to state public health data based on 2019 census numbers. Among eligible age groups, only those between 50 and 59 have less than a 95 per cent vaccination rate, with 92 per cent of people in their 50s receiving at least one dose of the vaccine.

As the Delta variant spreads across the country, Ms. Valley said that the hospital and boards of health have sent positive test samples off to the state epidemiology lab to be sequenced for variant testing. She said results could take as long as three weeks due to a backlog at the state lab.

The jump in Island cases mirrors state and national case rates, which have climbed since dropping precipitously in the wake of the initial vaccine push. But as vaccination rates have stagnated across the country, cases have slowly continued to rise.

Ms. Valley said on Monday that a number of the Island cases were connected, with two families with two positive cases, and one with three or four.

“No big groups, and no sense that it’s a cluster in any way,” Ms. Valley said. “Just various family members.”

While Ms. Valley did not know how many of the cases were connected to off-Island travel, contact tracing had shown that a couple of Covid-positive patients had traveled to Provincetown last weekend. Provincetown has seen a small case surge in recent weeks, with state officials expanding testing capacity in the outer Cape.

Ms. Valley said guidance has not changed due to the recent cases, and that previously-scheduled outdoor events were still a go. The Beach Road Weekend concert festival in Tisbury is scheduled to start Friday.

“Guidance has not changed on anything on this point,” Ms. Valley said. “Beach Road Weekend is still using the seating pod arrangement that was in place before different Covid measures were lifted, trying to give people separation . . . it’s not like 2019’s Beach Road Weekend.”

But Ms. Valley expressed frustration that cases were still rising, nearly 16 months after the pandemic began. She pointed to various factors, including the large summer population spike and the rainy weather, as possible explanations.

“I was really hopeful that our numbers would remain low. But just seeing the number of people on the Island, I wasn’t surprised that they went back up,” Ms. Valley said. “There are a lot of people here, a lot of people traveling here, and it is pretty crowded. And a lot of it also could be that there’s been pretty crummy weather, so people are spending more time inside than they normally would be.”

The Island has now had 1,527 confirmed positive cases since March of 2020.