Impact of COVID-19 outbreaks and border control measures on dengue cases in four Asia-Pacific countries

Non-pharmaceutical interventions (NPIs) and COVID-19-related border controls might have influenced global dengue transmission dynamics. Taking the imposition of travel restrictions during the pandemic as a natural experiment, this study aimed to explore potential associations between border restrictions and dengue prevalence in selected non-endemic and endemic Asia-Pacific countries during the pandemic using a retrospective prediction approach. Generalized Additive Models (GAMs) were employed to model dengue case trends from 2009 to 2019, characterizing transmission periodicity and incidence patterns during the pandemic. Correlation analyses were conducted to examine possible associations between air passenger arrivals and reported dengue cases across four countries in 2020, using passenger volume data. SARIMA models were used to estimate counterfactual dengue incidence in the absence of COVID-19-related NPIs, and predicted cases were compared with observed cases to assess deviations potentially attributable to control measures. Compared with the 2009–2019 epidemic seasons, dengue activity in China and Australia remained below historical levels in 2020, while Thailand’s activity was slightly lower than its historical peak, with cases fluctuating within the moderate-to-high range. Singapore’s dengue activity remained consistently above historical maximum levels. Correlation analyses suggested a positive linear association between international air passenger arrivals and dengue cases in non-endemic countries, with Pearson correlation coefficients exceeding 0.75; however, such associations were not apparent in countries with endemic (Thailand and Singapore). Retrospective predictions indicated that COVID-19-related border restrictions might be associated with lower dengue case counts in China and Australia (96.97% and 98.16% lower than predictions, respectively), whereas observed data in Thailand and Singapore were 79.62% and 164.31% higher than historical trend-based predictions. Prior to 2020, the four countries exhibited distinct seasonal dengue patterns. This study indicated that pandemic-related border controls might have influenced dengue trends in selected non-endemic countries but appeared to have a limited association in endemic settings, where local transmission remained predominant. These findings suggested that mitigating dengue importation required an integrated framework that synchronised risk-stratified screening for arrivals, vector surveillance, and strengthened multilateral collaboration. These insights offer a strategic roadmap for global efforts against the increasing threat of dengue.