The old flu needles used to be live virus up until some time in the early
80's- these ones routinely made people sick with a "mild" dose of flu- that
was sometimes very severe.

Now they're inactivated viral outer membrane protein. Some people still
react to the this vaccine and should avoid it.

As Todd said before it comes down to risk vs benefit. The risk/benefit ratio
is very high for tetanus, diphtheria and paediatric whooping cough vaccines.
It gets lower for other vaccines and is only about 300 to 1 for say
tuberculosis immunisation if you live in a developed country. ie for every
300 serious illnesses prevented there will be on serious reaction. Whereas
for most other vaccines the risk/benefit ratio is in the thousands.

The only diet that boosts your immune system is the Paleo diet.

Ben