Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services immediately for trouble breathing, swelling of the face or throat, widespread hives with weakness, sudden collapse, or difficulty waking your baby.
Seek urgent medical assessment if your baby develops repeated vomiting, significant abdominal pain, episodes of intense crying, draws their legs toward the abdomen, becomes unusually weak, or has blood in the stool.
These can be signs of intussusception.
Signs of dehydration, such as very few wet diapers, a very dry mouth, no tears when crying, or unusual sleepiness, also need prompt medical advice.
Contact your baby’s healthcare team during routine hours if mild vomiting, diarrhea, or irritability lasts longer than expected, if you are unsure whether a dose was swallowed, or if a follow-up appointment was missed.
Every sign above is quoted from the sofidex article on Rotavirus vaccine - what you need to know. If you are not sure, err upward — it is always reasonable to be checked.