Effectiveness of physical interventions in reducing respiratory virus spread

The spread of acute respiratory infections (ARIs), such as influenza, SARS, and COVID-19, poses significant global health risks. While antiviral drugs and vaccines are critical, physical interventions are essential to curb the transmission. This review, updated to include studies from the COVID-19 pandemic, evaluates the efficacy of various physical interventions. 
The update included 11 new trials (610,872 participants), bringing the total to 78 RCTs. Many trials occurred during non-epidemic periods and the 2009 H1N1 pandemic, with few conducted amidst the intense transmission environment of COVID-19. Settings ranged from hospitals in high-income countries to crowded urban areas in low-income regions. Adherence to interventions varied, affecting outcomes.
Medical and surgical masks likely make little or no difference in preventing influenza-like illnesses (ILI) or COVID-19-like illnesses and laboratory-confirmed cases. In healthcare settings, N95/P2 respirators have uncertain effects on clinical respiratory illness and may slightly reduce ILI but show little difference in lab-confirmed infections. Hand hygiene demonstrated a probable benefit in reducing ARIs by 14%, translating to 327 fewer events per 1000 people. Despite variations in adherence and outcome measurement, hand hygiene appears beneficial in reducing respiratory illness. The evidence on masks and N95 respirators is less definitive, with moderate certainty suggesting minimal impact on virus transmission. There is a critical need for large, well-designed RCTs to better understand the effectiveness of these interventions, particularly in high-risk populations.