India, Oct. 13 -- What explains the coronavirus disease's trajectory in Mumbai, Chennai, Delhi, Hyderabad, and Bengaluru? All five cities, among India's largest and most important, have been badly hit by the viral disease - and all five would appear to be witnessing a prolonged run of the disease, with some ebbs and flows. This columnist has hypothesised about this in the past, proffering factors such as population density as a possible explanation. A recent (October 5) article in peer reviewed journal Nature Medicine by Benjamin Rader from the Boston University's School of Public Health, Samuel V Scarpino from the Network Science Institute at Boston's Northeastern University, Moritz Kramer at the Department of Zoology at Oxford University, and others, claims that the "degree to which cases of Covid-19 are compressed into a short period of time (peakedness of the epidemic) is strongly shaped by population aggregation and heterogeneity". It adds that "epidemics in crowded cities have larger total attack rates than [in] less populated cities", that "in general, epidemics in coastal cities were less peaked and larger and more prolonged", and that infection trajectories in rural areas were likely to be peaked....