As of now, you will not need to test prior to going to SXM, assuming your boosters will not be more than 9 months old. You will just need to upload a copy of your vaccine records as part of the EHAS approval process.

For the return, again as of now, the BinaxNOW test taken in SXM the day prior to leaving is acceptable for return to the US. You will just need to show it to the agents at the SXM airport.

Links to the official information is included in the first 3 posts at the beginning of this forum.