1 doctor weighed in:

My 1 month old is due for a vaccine. How long after being vaccinated do I need to look out for a bad reaction? An hour a day a week?

1 doctor weighed in
Dr. James Ferguson
Pediatrics

In brief: Soon

Significant reactions will generally show up within the first hours and less often after 24 hours.
Any event more than 48 hours is unlikely to be vaccine related.One exception is a delay of 7 days or so when the MMR can produce fever and or a rash.This is less a "bad" reaction and more a sign the body is experiencing a mild measles from the vaccine virus.

In brief: Soon

Significant reactions will generally show up within the first hours and less often after 24 hours.
Any event more than 48 hours is unlikely to be vaccine related.One exception is a delay of 7 days or so when the MMR can produce fever and or a rash.This is less a "bad" reaction and more a sign the body is experiencing a mild measles from the vaccine virus.
Dr. James Ferguson
Dr. James Ferguson
Thank
Get help from a real doctor now
Dr. Jonathan Jassey
Board Certified, Pediatrics
14 years in practice
1M people helped
Continue
111,000 doctors available
Read more answers from doctors