The Martha’s Vineyard Hospital is now scheduling Covid-19 booster shots for all adults ages 18 and older, following last week’s Food and Drug Administration authorization, a hospital spokeswoman said Monday.

Individuals who received a second dose of the Pfizer or Moderna vaccine at least six months ago are eligible to make an appointment for a booster, communications specialist Marissa Lefebvre said in an email. Those who received a Johnson & Johnson vaccine more than two months ago are also eligible, she said.

Booster appointments for adults and vaccine appointments for adults and children ages 5-11 can be made online at covidvaccine.massgeneralbrigham.org/island.

There are limited slots available now, but Ms. LeFebvre said the hospital is working on increasing the number of available appointments.

“Please continue to check back online,” she said.

While the hospital is the principal dispenser of vaccines on-Island, a special Covid-19 vaccine bus visited the Island over the weekend to offer vaccinations to children ages five and older and school staff. The Island boards of health in collaboration with Island Health Care have brought vaccine buses to the Island at various times to accelerate the vaccination effort.

Meanwhile, the Island boards of health said 16 people tested positive for the coronavirus for the week ending Saturday, Nov. 20, and four more were considered probable based on symptoms and over-the-counter tests.

Eleven of the positive cases were in people who were fully vaccinated and three were in unvaccinated individuals. The vaccination status of one was unknown.

The weekly case count represents an increase of one from the previous week. The boards of health initially said 16 people had tested positive for the week ending Nov. 13, but later amended that number to 15.

In a two-day report issued Monday, the boards of health reported eight new confirmed positive cases Monday, and three new probable cases. No new cases were reported for Sunday.

Those testing positive last week included one child under 11, three between 20 and 29, three between 30 and 39, two between 40 and 49, three between 50 and 59 and four between 60 and 69.

The Island boards of health issue a weekly case report every Monday. Weekly cases of Covid-19 on the Vineyard reached a three-month low of four in early November before beginning to rebound.