It varies from year to year. The traditional seasonal flu intramuscular contains 4 different variants it targets, and sometimes the predictions of which sequenc

It varies from year to year. The traditional seasonal flu intramuscular contains 4 different variants it targets, and sometimes the predictions of which sequences to include are wrong. In those years you see sub 50% vaccine efficiencies against infection. Vaccine efficiency versus hospitalization is much better. But the same situation re: igG humoral antibodies from intramuscular vaccination not getting in your nose/throat/etc mucosa apply to flu vaccines. Most people only get intramuscularly vaccinated and so get upper respiratory flu infections and spread but are mostly asymptomatic and unaware. Actual vaccine efficiency for flu intramusculars is probably lower than reported due to the asymptomatic cases. I personally alternate between intramuscular flu vaccines and the Flu Mist intranasal flu vaccine (which you can get by request).