We have a cruise on the books for next spring, I have all my Covid-19 vaccines and boosters, and still no anti-bodies to fight off Covid. There is an approved drug here in the states, that will increase the anti bodies for those who have compromised immune systems. Evusheld is the drug name. Not sure if it is available everywhere. After getting the 2 injections, my anti bodies count was back to normal.
Will still take all the precautions, but my doctor is ok with traveling.