I understand that flu vaccines only offered limited time protection. That’s why doctors don’t give out the flu shots too early in the season.
How could that one be good for 30 years?
You will see some reports in the literature of resistance carried over from year to year. I believe that some people alive in 1918 (over 90 y.o. now), still have vestigial resistance to the Spanish Flu.
During the Avian Flu scare of a few years ago - much was said about flu vaccines taken many years ago offering no protection. Yet blood studies at that time showed just the opposite... Older people who had had the actual flu or a vaccine still showed anti-bodies to various strains of the flu...
However, this does not mean that a person who took the Swine Flu vaccine in 1976 will be spared from this new set of flu strains - but it could well mean a person would under go a milder reaction to the new infection while others without such a vaccination could fare much worse...
With influenza a little immunity could go a long way in survival. It could mean the difference between a three day fever, cough, runny nose, versus having severe bronchitis and/or pneumonia setting in on a debilitated very sick patient.
Offering flu vaccines early is good sense (if they are available)