Reduced Dengue Incidence During COVID-19 Restrictions in Sri Lanka From March 2020 to April 2021

Background: Dengue is a major public health concern in Sri Lanka. COVID-19 in Sri Lanka was first detected in January 2020, and has continued to be prevalent in the country since that time. The impact of public health measures imposed to restrict COVID-19 transmission on the incidence of dengue throughout the island and particularly its northern Jaffna district in the period March 2020 to April 2021 was determined. Methods: The incidence of dengue and COVID-19, rainfall and the public health measures implemented to contain COVID-19 transmission for each district in Sri Lanka were obtained from Government sources. The Seasonal Autoregressive Integrated Moving Average (SARIMA) model was used to predict the dengue incidence expected in March 2020 to April 2021, based on pre-pandemic data and this was compared with the actual reported incidence of dengue during the period of COVID-19 restrictions. Ovitrap collections of Aedes larvae were also carried out in the Gurunagar ward of Jaffna city in the Jaffna district during the 2020 and 2021 lockdown and the findings compared with data from 2019. Results: The reported number of dengue cases for the whole country from March 2020 to April 2021 was significantly lower than the numbers of dengue cases predicted from the five years immediately preceding the COVID-19 pandemic (2015-2019). Decreased numbers of dengue cases were reported compared to predicted numbers of cases in all 25 administrative districts in the country including the Jaffna district. Aedes larval numbers collected from ovitraps in the Gurunagar ward in Jaffna city during the COVID-19 lockdown period were decreased, with significantly lower proportions of Ae. aegypti than Ae. albopictus, compared with 2019. Conclusion: Public health measures that restricted movement of people, closed schools, universities and offices in order to contain COVID-19 transmission unexpectedly led to a marked reduction in the incidence of dengue in Sri Lanka, in contrast to Singapore. The differences between the two tropical islands have significant implications for the epidemiology of dengue.