2018-2019 flu vaccines protection:
There are many different flu viruses and they are constantly changing. The composition of U.S. flu vaccines is reviewed annually and updated as needed to match circulating flu viruses. Flu vaccines protect against the three or four viruses (depending on vaccine) that research suggests will be most common. For 2018-2019, trivalent (three-component) vaccines contain:
A/Michigan/45/2015 (H1N1)pdm09-like virus
A/Singapore/INFIMH-16-0019/2016 A(H3N2)-like virus (updated)
B/Colorado/06/2017-like (Victoria lineage) virus (updated)
Quadrivalent (four-component) vaccines, which protect against a second lineage of B viruses, contain:
the three recommended viruses above, plus B/Phuket/3073/2013-like (Yamagata lineage) virus
Effectiveness of even small increases in immunity from the flu vaccine can in fact make a big difference both on an individual and population level.
An overview of the CDC influenza surveillance ,http://www.cdc.gov/flu/weekly/overview.htm.,
CDC: MISCONCEPTIONS ABOUT FLU AND THE FLU VACCINE VIDEO:
https://youtu.be/f86mImyhaoc