2019 2020 2021 1st 2nd age ages april aug august avg before casedemic cases cause causes cdc charts covid criteria death deaths december dose epidemic fda flu group hospitalization hospitalizations icu injures july last lottery ltc mask may michigan michigancharts month monthly months nov november oct october order other percent positive pre prior safety sep september testing tests total under unintentional usa vaccine vaccines vaers vax vaxxed weekly whitmer years