posted on Mar, 9 2017 @ 05:45 PM
a reply to: rickymouse
They're not. You are looking at average efficacy against Influenza A, which is 43%. The efficacy versus Influenza B is 73%. Combined, these provide
an "overall" protection of roughly 48%, because this year, there are more cases of A than B.
It's difficult to project the overall spread or transmission rate of a particular Flu virus ahead of time. Human's move around in fairly predictable
patterns at the macro level, but are very hard to pin down individually over the course of any particular season. A total efficacy of 48% is pretty
good actually, as the vaccine is designed to provide some protection against multiple Influenza strains. Sometimes, as was the case during the 2014-15
season, the vaccine is not a good match for the actual spread of influenza in the wild. That year, the vaccine was only about 19% effective.