"We estimate that 20 percent of the population in the four affected administrative divisions could be affected by Cyclone Nargis," said Shannon Doocy, an assistant professor with the Center for Refugee and Disaster Response, who developed the vulnerability estimates with colleagues from the Bloomberg School's Center for Public Health and Human Rights, and from Lehman College.
"These are rough estimates, but our calculations could be of great help to relief agencies that are trying to provide aid on the ground," she added.
According to the calculations, the Ayeyarwady region was hardest hit, with 1.8 million people affected; another 1.1 million were potentially affected in the Yangon administrative division. At least 100,000 people in both the Bago East and Mon divisions were also affected.
The United Nations estimates that as many as 220,000 are missing following the cyclone and that 63,000 to 101,000 people were killed.
Major health threats for cyclone survivors include waterborne diseases such as typhoid, which has already been reported in some areas and potential outbreaks of dysentery from cholera and E. coli.
Measles outbreaks, which are common in settings of mass displacement, are a concern for children and a possible threat. Mosquito-borne diseases, particularly malaria and dengue fever, are prevalent in Burma and are also significant health risks.
"Right now, the risk of disease outbreaks in Burma is especially high-much more so than we've typically seen with tropical cyclones in past decades-because the humanitarian assistance so far has been delayed and woefully inadequate in scale," said Chris Beyrer, director of the Center for Public Health and Human Rights.