Zoonotic coronaviruses, including the one that caused severe acute respiratory syndrome (SARS), cause significant morbidityand mortality in humans. No specific therapy for any human coronavirus is available, making vaccine development critical forprotection against these viruses. We previously showed that recombinant SARS coronavirus (SARS-CoV) (Urbani strain based)lacking envelope (E) protein expression (rU-ฮ”E) provided good but not perfect protection in young mice against challenge withvirulent mouse-adapted SARS-CoV (MA15). To improve vaccine efficacy, we developed a second set of E-deleted vaccine candidateson an MA15 background (rMA15-E). rMA15-ฮ”E is safe, causing no disease in 6-week-, 12-month-, or 18-month-old BALB/c mice. Immunization with this virus completely protected mice of three ages from lethal disease and effected more-rapidvirus clearance. Compared to rU-ฮ”E, rMA15-ฮ”E immunization resulted in significantly greater neutralizing antibody and SARSCoV-specific CD4 and CD8 T cell responses. After challenge, inflammatory cell infiltration, edema, and lung destruction weredecreased in the lungs of rMA15-ฮ”E-immunized mice compared to those in rU-ฮ”E-immunized 12-month-old mice. Collectively,these results show that immunization with a species-adapted attenuated coronavirus lacking E protein expression is safe andprovides optimal immunogenicity and long-term protection against challenge with lethal virus. This approach will be generallyuseful for development of vaccines protective against human coronaviruses as well as against coronaviruses that cause disease indomestic and companion animals. ยฉ 2013, American Society for Microbiology.