With the impact of the new Omicron variant still unknown, cases of Covid-19 on the Island are back on the upswing, with 48 more people confirmed positive for the virus in just five days.

“We were expecting to see an uptick in the numbers when the holidays came, and our numbers are way up,” Tisbury health agent Maura Valley said in a phone interview Thursday. “I think we’re beginning to see the holiday surge.”

Cases had been climbing slowly on the Vineyard since early November. In their weekly report issued Monday, the Island boards of health said that in the week ending Saturday, Nov. 27, 19 people had received positive PCR tests for Covid-19 and three more had tested positive in over-the-counter tests.

Eighteen of the cases were in people who were fully vaccinated, and six of the 19 cases were part of a cluster at an unidentified construction site. Tradesmen from two different companies were affected, Ms. Valley said, adding that no new cases had been linked to that cluster.

But following Thanksgiving, from Sunday through Thursday, case numbers shot up with 48 more people confirmed to have the virus through PCR tests and nine more considered probable based on over-the-counter tests, according to the boards of health. The case spike mirrored the trend statewide, where 4,838 new cases were confirmed on Wednesday alone.

Ms. Valley said the boards of health have not been given new guidance from the state since the emergence internationally of the Omicron variant. As of Thursday, only two cases of the variant had been identified in the United States.

“We really don’t have enough information to make any informed decisions right now,” she said. “We’re just waiting for guidance from the Department of Public Health.”

Vaccines for the coronavirus, including third dose booster shots, are being made available by appointment at the Martha’s Vineyard Hospital. A new batch of appointments is released each Friday at 4 p.m. on the hospital’s online scheduling platform at https://covidvaccine.massgeneralbrigham.org. First and second-dose vaccines are available for anyone five years of age and older; people 18 and older are eligible for third dose booster shots.

As of Tuesday, 14,776 people had been vaccinated at the hospital and 2,793 had been given a third booster shot.

Ms. Valley urged people to get vaccinated, get a booster when eligible and wear masks when in public places.

“I am concerned with the holiday parties and social events,” she said. “I think people assume these events are safe and that is not necessarily the case. It just makes sense to take precautions.”