Good afternoon doctors. i am fully vaccinated with the phfizer vaccine since end of march. is it safe to take a cruise? does it matter if the cruise visits foreign or domestic ports? what about the possibility of the ship becoming quarantined?

Very likely protected. However many places (especially in the Caribbean) have low vaccination levels with corresponding relatively high incidence of coronavirus. Also, unless Cruise Line enforces mandatory vaccination you just don’t know Go on a cruise line with mandatory (and enforced) vaccine policy. Avoid crowds. N-95 mask while in port. Dine outside (or on boat). Have fun