BACKGROUND: Early public-access defibrillation (PAD) effectively improves the outcomes of out-of-hospital cardiac arrests (OHCA), but several strategies implemented to prevent the spread of coronavirus disease 2019 (COVID-19) could decrease the availability of PAD and worsen outcomes after OHCA. Previous studies have reported conflicting findings, and there is a paucity of nationwide observations. This study aims to investigate the impact of COVID-19 on PAD and OHCA outcomes using a nationwide OHCA registry in Japan, where PAD is well-documented. METHODS: This secondary analysis of the All-Japan Utstein Registry, a prospective population-based nationwide registry of OHCA patients, included patients aged ≥ 18 years with bystander-witnessed OHCA and an initial shockable rhythm who were transported to medical facilities between January 1, 2005, and December 31, 2020. The analytical parameters of this study were the proportion of patients who underwent PAD and patients with one-month survival with favorable neurological outcomes, defined as a cerebral performance category score of 1 or 2. We compared the data between 2019 and 2020 using a multivariable logistic regression analysis. RESULTS: During the study period, 1,930,273 OHCA patients were registered; of these, 78,302 were eligible for the analysis. Before the COVID-19 pandemic, the proportion of OHCA patients who underwent PAD and demonstrated favorable neurological outcomes increased gradually from 2005 to 2019 (P for trend < 0.001). The proportion of patient who had PAD were 17.7% (876/4959) in 2019 and 15.1% (735/4869) in 2020, respectively. The proportion of patient who displayed favorable neurological outcomes were 25.1% (1245/4959) in 2019 and 22.8% (1109/4869) in 2020, respectively. After adjusting for potential confounders, a significant reduction in the proportion of PAD was observed compared to that in 2019 (adjusted odds ratio [AOR], 0.86; 95% confidence interval [CI], 0.76-0.97), while no significant reduction was observed in favorable neurological outcomes (AOR, 0.97; 95% CI 0.87-1.07). CONCLUSION: The proportion of PAD clearly decreased in 2020, probably due to the COVID-19 pandemic in Japan. In contrast, no significant reduction was observed in favorable neurological outcomes.