The isolation requirement for active cases is 10 days—the length of time someone with COVID-19 typically remains infectious. Contacts are required to isolate for 14 days. This longer isolation is required because of the length of the incubation period for COVID-19 (the length of time someone may become infected after exposure).
A few jurisdictions have chosen a shorter isolation period for contacts to balance hardship of isolation against the risk of transmission, but all recognize that there will be increased transmission with a shorter isolation period.