The article discusses the ongoing outbreak of Covid-19, a respiratory disease caused by a novel coronavirus structurally related to SARS. The authors highlight the challenges posed by this outbreak for public health, research, and medical communities. They provide an epidemiological and clinical overview of the first 425 cases reported in Wuhan, China, noting that the median age of patients was 59 years, with higher morbidity and mortality among the elderly and those with coexisting conditions. The case fatality rate is estimated to be around 2%, but if asymptomatic or minimally symptomatic cases are included, it may be less than 1%. The transmission efficiency of the virus is high, with a basic reproduction number (R0) of 2.2, indicating that each infected person spreads the infection to an additional two others. Temporary travel restrictions have been implemented in several countries to slow the spread, but the virus is expected to continue to spread globally. The authors emphasize the need for robust research to develop vaccines and effective therapies, as well as the importance of understanding the pathogenesis of the disease to navigate the uncharted arena of this outbreak.The article discusses the ongoing outbreak of Covid-19, a respiratory disease caused by a novel coronavirus structurally related to SARS. The authors highlight the challenges posed by this outbreak for public health, research, and medical communities. They provide an epidemiological and clinical overview of the first 425 cases reported in Wuhan, China, noting that the median age of patients was 59 years, with higher morbidity and mortality among the elderly and those with coexisting conditions. The case fatality rate is estimated to be around 2%, but if asymptomatic or minimally symptomatic cases are included, it may be less than 1%. The transmission efficiency of the virus is high, with a basic reproduction number (R0) of 2.2, indicating that each infected person spreads the infection to an additional two others. Temporary travel restrictions have been implemented in several countries to slow the spread, but the virus is expected to continue to spread globally. The authors emphasize the need for robust research to develop vaccines and effective therapies, as well as the importance of understanding the pathogenesis of the disease to navigate the uncharted arena of this outbreak.