for all we know he has food poisoning or something else...
flu shots really don't do a whole lot, any maybe they do get flu shots? I really dont know but i would be suprised if they didnt.
Somewhere i remember being told that in a typical flu shot they try to predict ahead of time what strands will be bad this year and choose like 4-6 of them and thats what is used in the vaccine/nasal spray. There are literally hundreads or thousands of strands