Not great, but still prevented a lot of illness:
Based on data from 4112 children and adults, vaccine effectiveness was estimated to be 37% against influenza A and 50% against influenza B viruses. Influenza B was the predominant strain in December, but as of mid-February there was a sharp rise in influenza A cases.
“Interim VE [vaccine effectiveness] estimates are consistent with those from previous seasons, ranging from 40%–60% when influenza vaccines were antigenically matched to circulating viruses,” the authors of the article wrote.
In the study, influenza positive participants had a vaccination rate of 37%, compared with a 55% vaccination rate among influenza negative participants. This points to an association between vaccination and reduction of influenza risk.
“I think it gets lost in the narrative that while the flu shot prevents a percentage of infections, and some people will go and develop the flu anyway, even if they do, there's some evidence that it's attenuated, and that the complications from having the flu including death are lessened even if someone develops flu after they've gotten a shot,” Jason Gallagher, PharmD, FCCP, FIDSA, BCPS, clinical professor at Temple University College of Pharmacy and editor-in-chief of Contagion® said in an interview.