The following is advice from Public Health England with regards to children developing a fever following flu vaccinations:
Parents and carers should be advised that flu vaccination may cause a mild fever which usually resolves within 48 hours. This is a common, expected reaction and isolation is not required unless COVID-19 is suspected.
Feeling generally unwell, shivery, achy and tired are also commonly reported symptoms following vaccination with inactivated flu vaccine. Nasal congestion/runny nose, reduced appetite, feeling generally unwell and headache are common adverse reactions following administration of LAIV (the nasal spray flu vaccine). These symptoms usually disappear within 1 to 2 days without treatment but paracetamol can be given if necessary to relieve any of these symptoms.
As has always been recommended, any fever after vaccination should be monitored and if parents or carers are concerned about their child’s health at any time, they should seek advice from their GP or NHS 111.