Effectiveness of the vaccines depends on choices made months before it's needed.

Influenza comes in two main types, A and B. Flu vaccines always have two A strains -- an H1N1 and an H3N2 -- as well as a B strain (and an extra B in the quadrivalent vaccines.) And because the strains evolve and change from year to year, the vaccine has to change as well -- a new vaccine every year. it takes 6 months to produce the millions of doses of vaccine that will be needed. And in that time, the virus can shift (mutate its' genes to a different strain). http://www.medpagetoday.com/InfectiousDisease/URItheFlu/50305?xid=nl_mpt_DHE_2015-03-05&utm_content=&utm_medium=email&utm_campaign=DailyHeadlines&utm_source=ST&eun=g721819d0r&userid=721819&email=amydugan2@gmail.com&mu_id=5883165