I spent 30 years working in a medical field, and am very comfortable with the flu shot.I have asthma too but it's only really bad when there's really cold air. I am always offered the jab but I haven't got around to it yet - worried I'll be ill after the jab, but my friend has told me that they don't actually use live flu virus or whatever it is these days so the risk of even having a mild dose of flu from the jab has been eradicated, so I may have it this year.
There are 2 ways to get the flu despite getting the shot. The first way is if you were already exposed to the flu BEFORE getting the shot, so the flu is quietly incubating for a few days as it gears up to make you sick. Most people's immune systems need about 2 weeks AFTER GETTING THE SHOT to make enough antibodies to protect them. So as far as exposure and timing goes, either you're lucky or you're not.
The second way is also a matter of luck. There are LOTS of flu viruses going around at the same time. They simply cannot vaccinate everyone against ALL the flu types they're exposed to. So they pick the 2-3 most common ones and build the vaccine for those. So if the vaccine for this year protects you from flu types A, B and C but you get sneezed on by someone who has flu type E, you won't be protected and will get sick.
