Public health measures to stop the spread of Covid-19 had the unintended consequence of preventing as many as 720,000 dengue virus infections across Latin America and Southeast Asia in 2020. More than 5 million people were infected with dengue—also known as “breakbone fever” for its severe joint and muscle pain—globally in 2019. At the onset of the pandemic, infectious disease researchers feared disaster as resources were diverted to Covid-19. Measures like spraying for mosquitoes were interrupted. Researchers think severe disruptions in peoples' movement were responsible for the dengue decrease. School closures were key because the Aedes aegypti mosquitoes that spread dengue are daytime feeders, and feed at school or in workplaces. Dengue may also have declined during stay-at-home orders because infected people did not go out where new mosquitoes could bite them and then pass the virus on to other people.