Thank you for posting your question. Before answering your question I would like to inform you that 6 months is not a correct age for the first dose of rota virus vaccination. The course should have been completed by now. It is not ideally supposed to be given this late. Now coming to the symptoms, vomiting and decreased feeding are very non specific symptoms and could occur in a variety of conditions. In order to clearly determine the cause of such symptoms, their association with other symptoms like fever, diarrhea, cold, cough etc. should be studied. It is less likely(though not impossible) that the symptoms may be due to rota viral vaccine. There is a higher probability that it could be due to some viral infection of the gut or any other infection causing the child to refuse for feed. If there is associated cold, then nose block should be ruled out as it can also cause decreased feeding and it should be managed by applying nasal saline drops. Also reflex vomiting should be ruled out if there is associated cough. Here the baby will vomiting right after a bout of cough. Vomiting may be managed by antiemetic drug like moti norm. Make sure to keep the head end of the child elevated while asleep and keep the child well hydrated by frequent feeding. If the complained of decreased feeding continues or additional symptoms arise, a medical consultation should be taken. If you have any more doubts regarding this case, do reply back.