Thats very difficult to determine... those who have had the vaccine and don't develop flu symptoms won't go and tell the doctor "hey I haven't had the flu this year".
20 years ago many who were vaccinated developed flu symptoms because the vax wasn't well prepared... cost cutting and all that, y'know... More recently the efficacy of the "inactivation" process is improved as customers want the safety afforded by vaccination.
So many variables to develop accurate data, including people who don't go to the doctor... the largest proportion of the population.
As you can see in the chart I posted we don't have record vaccinations every year... the disinformation by anti-vaxxers had a significant impact and resulted in a massive spike in infections in 2017... have a look at the link as I suggested - or don't you want to know?
