The NY Times had a comprehensive article about NYC's preschool flu shot mandate last January 2015. I blogged about the issue here; and now, in December, a judge has thrown out the mandate.
Children aged 6 months to 5 years and who attended any preschool program licensed by NY City were required to receive a flu shot. The schools had to be the enforcers; if they failed to comply, they could be fined up to $2,000. This rule was imposed in 2014 under outgoing Mayor Bloomberg, by decree of the unelected Board of Health.
Only two states, New Jersey and Connecticut, have imposed similar preschool flu mandates. Preschool flu shots were not required elsewhere in NY state.
If the shots worked well, choosing to get one might be a good idea. But they work rather poorly. Estimates of efficacy range from 40% (CDC) to 1-3% (Cochrane Collaboration).
Because it is very difficult to assign side effects to vaccines, and because flu shot composition generally changes every year, it is impossible to know what the vaccine's side effects will be, until at least a year after the flu season is over. This means that it is very difficult to determine the risk versus benefit of a flu shot before you get one. Why subject our youngest citizens to vaccines for which both the benefit and risk are invariably unknown when they are used?
The judge ruled against the mandate on the basis that the NY legislature voted on other mandated vaccinations, and only the elected legislature, not NYC's health board, holds the authority to mandate vaccines.