How Covid restrictions led to drastic fall in dengue cases in 2020; Lancet study offers insights

As the government and local authorities ordered lockdowns to contain coronavirus pandemic, the move resulted in an unintended, albeit positive, outcome.

A Lancet research has found that the number of dengue cases fell drastically as public places were shut and people locked themselves in their houses. The researchers involved in the study estimate that historically low dengue incidence – 720,000 fewer dengue cases – occurred in 2020 globally, which is potentially attributable to Covid-19-related disruption which included restrictions on movement.

The article publised in The Lancet Infectious Diseases Journal says the said study is the first to analyse dengue data throughout 2020 from 23 countries spanning the main dengue endemic regions of Latin America and southeast Asia and might help in giving new insights into understanding and developing new and existing interventions for the vector-borne disease.

The findings of the study show that there is a consistent association between various measures of Covid-19-related disruption and reduced dengue transmission that cannot be explained by seasonal or extra-seasonal dengue cycles or underreporting.

The study noted that these declines occurred at the beginning of the dengue season in many countries, with cases in southeast Asia, Central America, and the Caribbean typically increasing between June and September.

Nine of 11 countries in Central America and the Caribbean, and the Philippines in southeast Asia, saw complete suppression of their 2020 dengue season, with most other countries experiencing a much suppressed dengue season. “In countries where public health and social measures began at the peak of the dengue season, such as in South America, sharper than expected declines were seen despite above average incidence earlier in the year,” says the research.

How the study would help in understanding dengue transmission better

While the Covid-19 restrictions brought the world to a halt, these findings provide a unique opportunity

to understand how different environments and human movement contribute to transmission and could lead to new interventions and strategies.

What factors led to reduction in overall cases

School closures in the public health and social measures model explained 70·95% of the reduction, whereas reductions in movement in non-residential locations in the human movement behaviour model explained 30·95%.

Monitoring of dengue trends in 2021 will be the key: Researchers

The study however says that it remains to be seen how many of these 720000 cases are truly averted or just delayed until later years as pre-Covid 19 human movement behaviours re-establish, adding, that continued observation and re-analysis will be needed to assess longer term effects.

“Continued monitoring of dengue trends in 2021 and beyond will be key, including the continued collection of human movement data, better data on adherence to public health and social measures,26 and the use of disease forecasting systems to detect and respond to dengue epidemics when they do occur,” noted the study.

The study concluded that “although it remains unknown what effect these restrictions will have on dengue dynamics in the long term, the unique circumstances of the Covid-19 pandemic might give new insights into the development and targeting of new and existing interventions for dengue.”