Fig 1.
The timeline of a series of mass gatherings and public demonstrations in Hong Kong in mid-2020.
Fig 2.
Daily COVID-19 new cases diagnosed in Hong Kong.
Source: Centre for Health Protection under the Health Department, https://www.chp.gov.hk/en/features/102997.html.
Table 1.
Distribution of sample weights in the donor pool for synthetic Hong Kong.
Table 2.
Pre-intervention balance of predictor variables in Panel A (June 20 as the intervention point).
Fig 3.
Impact of mass gatherings (after the lift of POGGR) on COVID-19 new cases.
Fig 4.
Impact of mass gatherings (after the lift of POGGR) on COVID-19 total cases.
Fig 5.
Impact of mass gatherings (after the lift of POGGR) on the number of new cases of COVID-19 (with intervention point changed).
When we changed the intervention point (i.e., the starting date of lifting of public gathering restrictions in Hong Kong), we obtained different estimates of new cases in the respective synthetic controls. However, the adjusted results still show that the actual number of daily new cases of COVID observed after the lift of public gatherings and the occurrence of and demonstrations is, in general, higher than the counterfactual estimated in the synthetic controls obtained in all the Panels. Except for Panels I, J, and K, other Panels using an earlier intervention point indicate that the counterfactual estimates of new case numbers are initially close to the actual number. After some fluctuations, the synthetic trends stabilize in the later stage, while the actual infections numbers grew sharply. If we impose longer lags (as in Panel I, J, and K), meaning that we have a later intervention point, the gap between infection numbers under the two scenarios becomes more significant even in the early stage of the intervention.
Table 3.
Summary of the impact of mass gatherings (after the relaxation of social distancing policy) on the increase of new cases during the 10-day and 30-day periods after intervention, taking June 20 and each of the 10 days afterward as the intervention point.