Rio de Janeiro reports least amount of dengue cases in a January in 20 years Aedes aegypti/CDC 2005 was the previous low in a January when 67 cases were reported. Also according to analysts at the Rio 21 Institute, it appears that the pandemic caused by the Coronavirus contributed to the non-occurrence of so many cases of Dengue in the city of Rio, as the numbers for 2020 and 2021 show a strong downward trend . The month of January had less rain than normal in the city of Rio is also pointed out as an important factor, because it ends up generating less standing water, where the female of the Aedes mosquito deposits its larvae.