(1/7) Worrying indications that the second wave of COVID-19 has now begun in Hong Kong, with more than 50 local infections being identified in the past few days and a large number expected to be reported later today.
(2/7) Our estimate of the effective reproductive number "Rt" for local infections is close to 3, which is concerning covid19.sph.hku.hk It will take a lot of effort to bring down such a high reproductive number. 
(3/7) Clusters have been identified in an elderly home, a public housing estate, and linked with some restaurants. Test+trace has not prevented this. Mask-wearing in public is still universal, and has not prevented this. scmp.com/news/hong-kong…
(4/7) In our analysis of the first wave, we estimated that Rt rose above 2 in late March. This occurred even though we were doing a lot of testing and contact tracing, everyone was wearing face masks, schools were closed, and mass gatherings discouraged.
(5/7) Implementing work-from-home for civil servants and private businesses, closing bars and leisure facilities, and enhancing social distancing in restaurants was able to bring the first wave under control, and hopefully similar measures will be able to halt this second wave.
(6/7) How did the second wave start? We may never know, but given the absence of local cases for most of the past 3 months, these latest outbreaks may have been started by relatively more recent importations.
(7/7) When the second epidemic is controlled, this really emphasises the importance of keeping infections out through effective testing and quarantine of persons arriving in Hong Kong. Once an epidemic begins, it will take a lot of effort to stop.
