i had a travel vaccine two weeks before my first attack too so i can understand your trepidation - but i'm sorry i don't know anything about the yellow fever. certainly my travel vaccine (hepA) was from the picorna family of viruses that as far as i recall are potentially implicated in ms. here's some stuff i found
The following vaccines have been evaluated in people with MS:
Other vaccinations such as those for pneumonia, meningitis, typhoid, polio, yellow fever, and hepatitis A vaccination, do not have published studies addressing their safety in MS. Nevertheless, the clinical practice guideline recommends that people with MS who meet the CDC criteria for these vaccinations should be given them. CDC criteria can be viewed at: http://www.cdc.gov/ncidod/guidelines/guidelines_topic_vaccination.htm
which points you to a list from which you can pick this:
and from what i can see, the section on altered immune status is relevant
Infection with yellow fever vaccine virus poses a theoretical
risk for encephalitis to 1) patients with acquired immunodeficiency
syndrome (AIDS); 2) patients who are infected with
HIV and have other manifestations of HIV infection (32); 3)
patients with leukemia, lymphoma, generalized malignancy;
or 4) those whose immunologic responses are suppressed by
corticosteroids, alkylating drugs, antimetabolites, or radiation.
Such patients should not be vaccinated.
so, guess it depends what you're taking???