To reach Saba, you must depart transit through the major airline hub of St. Martin (Sint Maartin is the Dutch spelling), 15 minutes away in a 16 passenger Twin Otter (a ferry is available that takes a few hours, which you reach by taxi from the St. Martin airport).
To visit the Dutch Caribbean islands of Sint Maartin, Saba, Aruba, Curacao, Bonaire and Sint Eustatius (Statia), you must be vaccinated, COVID free, and low risk. Before departure, you must fill out an online EHAS form to receive a QR code that you must present to the airline gate agent before departing the U.S.. You'll need at least 12 hours to complete this process, maybe more, so you'll need to do it the day before, You'll provide your demographics, passport data, etc., and upload your COVID vaccination certificate and a recent COVID virus test. Some passengers departing the US on my flight to St. Martin did not have this completed and approved, and they were not allowed to board.
You won't be able to complete this EHAS form and process a couple of hours before boarding your flight because it must be reviewed by officials before you are approved. Frustratingly, it took me a second attempt; about half of our group had to undergo a group remedial session with the successful applicants to get it right. The complexity led to a big disappointment for me, as my long-time dive buddy Marty, who was departing on a different flight than the rest of us, couldn't attend our remedial session. Working alone, he became so frustrated with the EHAS application and the lack of support, he gave up on the trip and went home. Rather sad for both of us.
For the return trip to the USA, per U.S. regulations, you will need a negative COVID test, taken a day before departure from Saba.