Covid-19 and the mitigation measures taken to limit its spread have significantly disrupted essential health services and other disease control programs worldwide. During periods of rising Covid-19 infections, governments implemented measures such as school closures, lockdowns and social restrictions, aiming to suppress the rate of SARS-CoV-2 transmission. These restrictions resulted in behavioural changes that affected the transmission of other infectious diseases, including dengue virus.

Dengue is a mosquito-borne viral infection that has continued to pose a significant public health challenge in endemic countries. Until now, the overall impact of the Covid-19 pandemic on dengue incidence has been unclear. A recent study by Chen and colleagues published in Lancet Infectious Diseases, however, identified a significant decline in annual dengue cases in 2020 in select markets, potentially due to Covid-19 related disruptions. As such, GlobalData epidemiologists expect to see a temporary decrease in the diagnosed incident cases of dengue in Mexico and Thailand.

In the study conducted by Chen and colleagues, the incidence rates of dengue were compared in 16 countries across Latin America (Venezuela, Jamaica, El Salvador, Dominican Republic, Honduras, Panama, Guatemala, Belize, Ecuador, Mexico, Nicaragua, Brazil, Peru, Columbia, Bolivia and Costa Rica) and seven countries in South-East Asia (Philippines, Cambodia, Vietnam, Laos, Malaysia, Thailand and Singapore). The model predicted incidence using country-specific data on monthly case numbers, climate and population variables from 2014 to 2020 obtained from the World Health Organisation (WHO) weekly reports. Across all 23 countries included in the study, researchers estimated that there were 720,000 fewer incident cases than expected in 2020. In particular, it was estimated that Mexico averted 115,000 incident cases, while Thailand observed 225,000 fewer incident cases of dengue during 2020.

According to GlobalData epidemiologists, lab-confirmed annual incident cases of dengue in Mexico and Thailand have trended upwards in recent years and are expected to reach around 80,000 by 2023. The impact of the Covid-19 pandemic will likely drive a decrease in the diagnosed incident cases of dengue in these markets, resulting in diagnosed incident cases falling below current forecast estimates. These changes may, however, be temporary as the impacts of the Covid-19 pandemic lessen over time.

There are several plausible explanations for this marked decrease in the incidence of dengue. In the initial stages of the pandemic, there was a reduction in treatment-seeking behaviour for other illnesses besides Covid-19. This was compounded by the reduced availability of lab-testing equipment for dengue, which may have increased the misdiagnosis rate. In addition, the record-breaking dengue outbreaks in the Americas and South-East Asia in 2019 may have resulted in high levels of population immunity to dengue. In this case, fewer individuals would have been susceptible to the virus in 2020, contributing to the lower case numbers being observed.

Chen and colleagues also found a strong association between societal disruptions due to Covid-19 and reduced dengue risk. In particular, school closures and spending less time in non-residential areas were most strongly linked to reduced dengue risk. This emphasises the importance of understanding movement patterns during epidemic settings and highlights an area for additional research. Historically, dengue control has centred around vector control interventions. In the event of future epidemics, however, health officials may also evaluate whether measures such as contact tracing, testing or quarantines could help control the spread of the virus.