ObjectiveTo examine whether post-outbreak early-phase interventions by emergency response teams (ERTs) in long-term care facilities (LTCFs) contribute to containment with lower incidence and case-fatality rate of COVID-19 and analyse the required assistance.MethodsRecords from 59 LTCFs (28 hospitals, 15 nursing homes, and 16 homes) assisted by ERTs after the COVID-19 outbreak, between May 2020 and January 2021, were used for the analysis. Incidence and case-fatality rates among 6,432 residents and 8,586 care workers were calculated. The daily reports of ERTs were reviewed, and content analysis was performed.ResultsIncidence rates among residents and care workers with early phase (<7 days from onset) interventions (30·3%, 10·8%) were lower than those with late phase (≥7 days from onset) interventions (36·6%, 12·6%) (p<0·001, p = 0·011, respectively). The case-fatality rate among residents with early-phase and late-phase interventions were 14·8% and 16·9%, respectively. ERT assistance in LTCFs was not limited to infection control but extended to command and coordination assistance in all studied facilities.ConclusionAssistance in the facility’s operational governance from the early phase of an outbreak in LTCFs contributed to a significant decline in incidence rate and case fatality rate among LTCF residents and care workers in facilities.