The Martha’s Vineyard Hospital is now offering second booster shots of the Covid-19 vaccine to anyone over the age of 50 and people with certain medical conditions.

Individuals must have received their first booster (third dose) at least four months ago to be eligible for another booster. Both the Pfizer and Moderna vaccines are available.

Appointments for Tuesdays, Fridays and Saturdays can be scheduled online at https://covidvaccine.massgeneralbrigham.org/island.

The Food and Drug Administration announced Tuesday that it had authorized second boosters for people over 50 and those at high risk.

Medical conditions that are considered high risk are listed here.