Davemk said:
I am quoting CDC statistics. I have no idea how they come up with that number. They(CDC) are already reporting that this years flu shot will have an even lower efficacy rate.
The process for producing vaccines involves the same challenges for a wide range of pathogens not just influenza viruses. Microorganisms change rapidly and there are many serovars with in the same species.
I looked at the specific efficacy reports you mentioned but I also found this. At the end of the day, if you are in a high risk group, any level of efficacy is worthwhile.
How effective is the flu vaccine?
CDC conducts studies each year to determine how well the influenza (flu) vaccine protects against flu illness. While vaccine effectiveness (VE) can vary, recent studies show that flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well-matched to the flu vaccine. In general, current flu vaccines tend to work better against influenza B and influenza A(H1N1) viruses and offer lower protection against influenza A(H3N2) viruses. See "Does flu vaccine effectiveness vary by type or subtype?" and "Why is flu vaccine typically less effective against influenza A H3N2 viruses?" for more information.