Temporal trends in containment measure effectiveness against Omicron variant during China's zero-COVID policy, 2022

Highly transmissible Omicron variants challenged control, especially in settings with limited prior population immunity. Whether non-pharmaceutical interventions (NPIs) effective against earlier variants retained effectiveness against Omicron remained unclear from real-world data, particularly in settings without substantial confounding from prior infection- or vaccine-induced immunity. In mainland China, Omicron outbreaks occurred with increasing frequency during 2022 under the zero-COVID policy until relaxation in December. Understanding containment measure effectiveness against highly transmissible variants is critical for pandemic preparedness, whereas real-world evidence on this is limited. We evaluated the real-world effectiveness of containment measures during this critical transition period. We analyzed 53 Omicron outbreaks across 30 provinces in mainland China from January to November 2022 using interrupted time series analysis. We identified 92 containment measure intensity level increases and estimated incidence rate ratios (IRR) and differences in growth rates (DGR) using province-specific Poisson regression models with 7-day intervention lag and 30-day pre-/post-intervention windows. We assessed temporal trends and compared effectiveness across measure types (school closures, workplace closures, mass gathering restrictions, public transport closures, and lockdowns) using meta-regression. Among 92 intensity level increases, the median reduction in incidence was 70% (IRR = 0.38), with 47% showing statistically significant reductions. The median decrease in growth rate was 0.15 units per day, with 63% statistically significant. Effectiveness declined over time, with measures implemented after June showing significantly lower impact than those before June (p < 0.05 for growth rates). Meta-regression revealed that intervention packages including lockdowns demonstrated significantly greater effectiveness (IRR = 0.32; 95% CI 0.14, 0.74) compared to packages without lockdowns, while other measure types showed similar effectiveness. Containment measures significantly reduced Omicron transmission in China, though effectiveness declined over time. Lockdown measures showed superior effectiveness. These findings inform future pandemic preparedness regarding the potential and limitations of intensive containment strategies against highly transmissible variants.