>>if some sort of freakish new flu were to appear, can't they make a vaccine like they do every year of the most popular ones and vaccinate people?<<
No, because it spreads too fast. It takes 6-7 months to change the vaccine.
That's true. The flu vaccine they prepare each year is really a guesstimate of what flu will be prevalent that year. Sometimes they pick the wrong strain, and the vaccine is ineffective.