Of 364 older Danes who were seropositive for H3N2 infection and about 1000 who were negative, it turned out those who were positive were a bit more likely to have been vaccinated this season for flu.
This may mean the vaccine was of no use due to high rates of mutation. Or it could mean the vaccine-induced antibodies made you more likely to get sick. (I have previously talked about the concept of blocking antibodies, which have occasionally been seen after introduction of a new vaccine, increasing the propensity to get the disease you are ostensibly being protected from. The new vaccine is soon taken off the market.)