Antivirals for treatment and chemoprophylaxis [21, 22] Mitigation: reduce illness severity and complications if administered early; reduce transmission from those receiving treatment; sometimes also used as chemoprophylaxis in high-risk circumstances Provide significant population-level protection or allow containment Attempts at source containment were not possible, as the pandemic was effectively already in WHO Phase 5 when what became the pandemic virus was first identified [22] . Initial observational studies suggest antivirals were successful when early treatment was administered Canada Germany Hong Kong SAR Japan UK US (these populations attempted the intervention initially but effort was not sustained towards the later stages of the pandemic)