Yup. Also big on importing immigrants. They bring the strains which the native population don't have immunity to. Even to the extent vaccines work, they're fairly specific, and aren't even 100% effective against the very strains they were designed to protect against. They're useless against foreign strains.
There are many reasons multi-culturalism (read: multi-racialism) isn't healthy for a populace, but infectious disease is a big one that isn't talked about bc "muh racism" and "muh equality." It creates a temendous tax on our immune systems to constantly fight novel, foreign infectious agents. It's a war of attrition you're more likely to lose the longer/more you're around immune challenges of this nature.