We went on the Baltics cruise last year. RSSC does not require vaccinations for this itinerary.
We did take precautions in St. Petersburg/Moscow as far as eating off ship. We dined off ship once during our three day stay in St. Petersburg, during our day excursion to Moscow, at the Cafe Pushkin. We were extremely selective in what we ate, choosing only very hot, well-cooked foods. We didn't consume salads or tap water. On previous sailings, many people reported becoming very ill after eating in restaurants in St. Petersburg and Moscow - Beth and Judy can address this, as it happened to both of them.