Your points are well taken and very informative. It would be interesting to know what vax the SSCA seminar said was only good for 6 months. That would be quite unusual, in my experience. Honestly, and not knocking the SSCA, but I would caution anyone who needs this info to get it from their family doctor, the CDC, the local health dept or a travelers medical clinic and not the SSCA. IMHO.
Here is a link to the CDC page that might be helpful:
As it reads, there are only a handful of vax required for the caribbean: Hep A, HepB, Rabies (if you think you will be exposed), typhoid (pills) and YF. The shortest period of protection for any of the above is 5 yrs.
And as you rightly point out, there are other therapeutics to be considered such as anti-malarial prophylaxis.
I would expect that anyone from the US and Europe cruising with children would already have had them immunized for dpt and measels.
Always check with your personal doctor first. Not all vaccines are indicated for all people and personal medical issues much always be taken into account.
It can also be important to check info for specific countries.
My best to all