The COVID-19 (SARS-CoV-2) pandemic has not yet ended. The COVID-19 pandemic has been the worst human health crisis after the Second World War [1]. Over 90% of SARS-CoV-2 cross-infections occur in confined spaces (e.g., buildings and transportation cabins), which reveals that confined environments and their associated air systems are vulnerable to infectious disease transmission. Evidence of SARS-CoV-2 indoor transmission has been documented, such as in residential buildings [2], hospitals [3], restaurants [4], offices [5], airport terminals [6], aircraft cabins [7], high-speed trains [8], buses [9], and ships [10], etc. Vaccination has played a crucial role in dampening the SARS-CoV-2 risk; however, it still may not be able to terminate the pandemic in the near future due to the possibility of continuous virus variation. In addition to improving the vaccination rate and vaccine effectiveness, strategies that can reduce the human exposure to various infectious pathogens are pressingly needed, both during and after the pandemic. The experience obtained and lessons learned from one event will always provide great insights into the handling of similar ones in the future.