why do we get to generalize mRNA vaccines, but not SARS-Cov-2? We've known about coronaviruses since the 1960s, we've had MERS, SARS, and other more recent ones

why do we get to generalize mRNA vaccines, but not SARS-Cov-2? We've known about coronaviruses since the 1960s, we've had MERS, SARS, and other more recent ones. https://www.cdc.gov/coronavirus/types.html https://www.cdc.gov/coronavirus/types.html I don't think we have long term information on either SARS-Cov-2 or the vaccine...