I got my flu vaccine on Wednesday. We are leaving town in 2 weeks, and will be around tons of people in airports and breathing recirculating air on planes and I wanted to be protected before then.
The worst case I ever had of the flu was waaaaay back when I was in my late 20's during the month of September. I was on vacation at Club Med in Cancun. I don't know if it is any different these days at Club Med's, but back then probably 99% of the guests stayed for a week and arrived and left on Saturdays. So a mass exodus of guests going home and arrival of new guests every Saturday from all over the world.
This particular week in September, the resort was fully booked, about 700 people. By Tuesday, a few people had come down with the flu. Aches, chills, high fever, upper respiratory, sore throats -- all the classic symptoms of influenza. If a few people have it, you can be sure there are others in the incubation period that aren't showing symptoms yet but are shedding the virus. The resort had these beach parties on Tuesdays where they played drinking games and passed around the same bottle of sangria during the game and by Thursday 1/3 of the guests had the flu and the infirmary had been totally wiped out of aspirin. The flu, in the heat, with no aspirin.
Looking back, it's interesting to see how quickly it spread in a "closed population," with everyone arriving on the same day and and then leaving on the same day.
Another interesting thing is that only a handful of the employees came down with the flu. I suspect that was because they were out in the sun so much and they had very healthy levels of vitamin D, which plays a huge roll in being able to fight off illness. In addition to the flu vaccine, vitamin D is in my arsenal to prevent the flu and colds:
Epidemic Influenza And Vitamin D - Medical News Today