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Tracking Transmission The rapid transmission dynamics of the disease have been a focus of our work from the outset. Since publishing early findings in January on the spread of the disease, described on page 10, we have continued to deepen knowledge about the infectiousness of SARS-CoV-2 and how it might be controlled. » Some patients infected with COVID-19 were shown to be shedding the virus 2-3 days before the first symptoms appear – an early and important finding concerning infectiveness. » The eyes were singled out as an important route of infection after a study showed SARS-CoV-2 can infect human airways and eyes more efficiently than SARS. SARS- CoV-2 was also detected in the conjunctival secretions of patients without ocular symptoms, suggesting this is a possible route of transmission. » Prolonged survival of the virus on smooth surfaces highlighted that the virus may be transmitted indirectly via contaminated fomites and hands. » Shedding of the infectious virus was shown to occur for at least 9-10 days after the onset of symptoms, a finding that led the Hong Kong Hospital Authority and WHO to amend their policy on discharging patients from hospital isolation. a. Transmission network of the “bar and band” cluster of undetermined source ( n =106). b. Transmission network associated with a wedding without clear infector-infectee pairs but linked back to a preceding social gathering and source ( n =22). c. Transmission network associated with a temple cluster of undetermined source ( n =19). d. All other clusters of SARS-CoV-2 infections where the source and transmission chain could be determined. “Superspreading” was shown to be a feature of COVID-19 in a study that used contact tracing data to identify all clusters of COVID-19 in Hong Kong from January 23 to April 28. 14