My husband suffers from hayfever, but never abroad. A friend who was studing her PHD in pollen(!) said that every country has different pollen and you have to become allergic to it. So if you are in a country for a short time you are not exposed to it long enough to get hayfever. If you moved to Orlando then you would eventually get hayfever.
If somebody knows otherwise then please correct me, but we have never had a problem.