Severe Acute Respiratory Syndrome ("SARS") is a human respiratory disease of recent origin, widespread infectivity, recurring incidence, and significant mortality. Although there is abundant evidence suggesting that the coronavirus responsible for the disease ("SARS-CoV") evolves during an outbreak, there is currently little data on the earliest strains of this coronavirus. The present invention is directed to the characterization of the genomic RNA sequences of these earliest SARS coronaviruses, to the identification of nucleotide positions within the SARS-CoV genomic RNA that are characteristic of the different evolutionary stages of the coronavirus, to kits based on these positions for use in diagnosis of the disease in patients, and for the development of vaccines to the disease based on the lowered virulence and contagiousness of these earliest strains of SARS-CoV.