Many people arriving because of wrong influenza jabs (6)
I believe the answer is:
influx
'many people arriving' is the definition.
(I've seen this before)
'because of wrong influenza jabs' is the wordplay.
'because of' becomes 'in' (I can't explain this - if you can you should give a lot more credence to this answer).
'wrong' becomes 'x' (X is used to mark something as incorrect).
'influenza' becomes 'flu' (synonyms).
'jabs' is an insertion indicator (some letters jab into others).
'in'+'x'='inx'
'inx' going around 'flu' is 'INFLUX'.
Can you help me to learn more?
(Other definitions for influx that I've seen before include "Arrival - invasion" , "Inward flow" , "Act of flowing in" , "Mass invasion" , "Process of arrival" .)