COVID-19 | A new study that analysed the coronavirus outbreak in Brazil has found a link between the spread of the virus and past outbreaks of dengue fever that suggests exposure to the mosquito-transmitted illness may provide some level of immunity against Covid-19.

The study which has not been published is led by Miguel Nicolelis, a professor at Duke University, and was shared exclusively with Reuters. It compared the geographic distribution of coronavirus cases with the spread of dengue in 2019 and 2020...