When recovering from my heart attack at the Norfolk & Norwich hospital I met a young man aged about 28-30ish who was waiting for a heart transplant...sadly I am told he did not get one in time and died.
He told me he had caught flu but had continued to work through it as a builders labourer as they had an urgent job to complete...he had kept going by continually taking Lem Sips....apparently the flu symptoms were masked and he managed to keep going and complete the job but it turns out the flu had damaged his heart to the extent he now needed a transplant.....He advised me he now knew you should not do manual work if you have flu and you should see a doctor and follow their advise and treat flu seriously...just like the NHS does by providing flu shots.
Probably this may be good advice to aircrew.