I'm getting mine next week. Thiomersal is the ingredient you should look out for if you want to avoid mercury but there are vaccines without or with negligable amounts of thiomersal ni them.
I had to look into this as I'm currently 24 wks pregnant, do need to flu vaccine, and didn't want to use one with any mercury.
One year about 11 years ago I had a huge reaction to a flu vaccine - got a severe asthma attack that landed me in hospital, but I've had 4 or 5 flu vaccines since then and nothing happened. I think sometimes I can really wipe you out, maybe you're fighting off another bug at the time....or something unscientific like that