logic - There is no serious immediate side effects.
But even the doctors are unsure about the longterm side effects.Its true that the FDA have approved the vaccine. But....

37% people refused in Canada. The reaction is almost the same allover.
Old H1N1 vaccine had some issues , few had even the deadly Gullllain Barre Syndrome after months.

H1N1 2009 vaccine's batch of 170000 shots were withdrawn due to some reactions in the US earlier.