The CDC has been studying the Flu vaccine effectiveness (VE) regularly assess  since 2003-4 to confirm the value of flu vaccination as a public health intervention.  Unfortunately, the flue vaccine effectiveness has not been that high as seen in this CDC table.

It is interesting that the influenza vaccine has very limited effectiveness and is often no higher than 50% effective yet experts still advocate for its use.



Source: Seasonal Influenza Vaccine Effectiveness, 2005-2016 Error processing SSI file