SARS stands for severe acute respiratory syndrome. In 2003, an outbreak of SARS started in China and spread to other countries before ending in 2004. The virus that causes COVID-19 is similar to the one that caused the 2003 SARS outbreak: both are types of coronaviruses. Much is still unknown, but COVID-19 seems to spread faster than the 2003 SARS and also may cause less severe illness.