Last trip I made to Africa we had to take Africa: hepatitis A, hepatitis B, typhoid, cholera, yellow fever, anthrax , meningitis , measles, mumps and rubella , tetanus, diphtheria and pertussis (Tdap), influenza, pneumonia , and polio. (Some were just boosters)
But I was sick as a fucking dog for a week after that shit , I don't know what exactly caused what but I ran a moderate fever , severe stomach upset and full body ache for a solid 10 days.
I haven't taken the flu shot since I've been home but I keep my vitamins high including D3 as Tom mentioned and I've never gotten the flu.