If you think about it, people getting the flu shot and injecting the flu into themselves and then spreading that around their workplace or their home, etc, that made the seasonal flu worse each year than it normally might otherwise. The vaccine itself expanded the flu into places it might not have reached so readily.
You might say the purpose of the vaccine was really to help spread the flu. Because the vaccine never did anything, people could still end up getting the flu at any time after getting the vaccine.