This study showed that border restrictions, quarantine and isolation, distancing, and changes in population behavior were associated with reduced transmission of COVID-19 and influenza in Hong Kong.

Hong Kong has engaged in a number of measures to handle the COVID-19 pandemic. Researchers analyzed data on COVID-19 cases, influenza surveillance data in outpatients, and influenza hospitalizations in children. They then estimated the daily effective reproduction number (Rt) for COVID-19 and influenza A H1N1 to explore changes in transmissibility over time.

They found that COVID-19 Rt has remained at approximately 1 for 8 weeks in Hong Kong. That means that each infected person infected one other, so the outbreak was in steady state. Influenza transmission declined substantially after the implementation of social distancing measures in late January, with a 44% reduction from an estimated Rt of 1·28 before the start of the school closures to 0·72 after. Similarly, a 33% reduction in Rtwas found based on pediatric hospitalization rates, from an Rt of 1·10 before the start of the school closures to 0·73  after.