The pace at which the coronavirus spreads globally appears to have a link to the latitude nations occupy, according to an epidemiological study undertaken by an eminent institution in Chennai. The study by the Institute of Mathematical Sciences (IMSC), an autonomous organisation under the Centre’s Atomic Energy Department, also projected the number of active COVID-19 cases in India could be around 400 on coming Wednesday and 900 in the worst case scenario.
Importantly, whether the active cases will rise or go down depends on factors like people”s response at the individual level and support to the ongoing government measures to tackle the virus, Prof Sitabhra Sinha, who, along with Soumya Easwaran of the institute, has taken up the study, said.
As on Sunday morning, the number of confirmed COVID-19 cases in the country stood at 324, with the last two days seeing a sharp rise.
While analysing various factors, the two-member team of the institute, dedicated to research in areas including theoretical Physics and Mathematics, stumbled on the possible latitude link to the spread of coronavirus. “Regions at higher latitudes in general have a higher rate of growth of the epidemic (for instance Denmark),” Sinha said.
The range of latitude that was studied varies between that of Denmark which is at 56 degrees north and Singapore close to the equator and the higher latitude countries typically showed higher rate of spread, he added.
The study also found no link between weather conditions and the rate of spread of the virus, which has claimed over 11,000 lives across the world, prompting authorities, including in India, to announce lockdowns to contain it.
The seeming correlation between the latitudinal positions of the countries and the rate of dispersion of the pathogen, will be strengthened by further analysis which is on, the researcher said.
Topping the list of the highest Ro (reproduction number) was Denmark 3.35 followed by the Netherlands at 3.19 and both these nations occupy a high latitude, he said.
The Ro, an epidemiological jargon referring to an average number of people a single infected person could infect in a given population, for India, however, is low at 1.7.
Explaining with data on the spread of coronavirus in China and other Asian countries including India, several European nations and the USA, Sinha said they attempted to see whether the variation in the growth rate of the number of infected persons in different regions could be related to some factors and then they zeroed in on geographic latitude for deeper examination.
According to him, Qatar has an Ro of 3.06, and is followed by Switzerland (2.96), Spain (2.74), Iran (2.73), Germany (2.58), US (New York) (2.49) and Italy (2.34). China’s Hubei province has an Ro of 2.14, which was the epicentre at the time of outbreak of the virus. “As the figure shows, there is a correlation between latitude and Ro for a given place. Regions at higher latitudes in general have a higher rate of growth of the epidemic (for instance Denmark).
“Initially, we thought this suggested a temperature dependence, with places in hotter climates showing a slower growth. When we plotted Ro against temperature; to our surprise we found that there was no correlation whatsoever,” he said. Temperature is one of the elements of weather observed anywhere.
Further, Sinha said based on inputs from colleagues they were now looking at “daylight duration or sunlight exposure which should be strongly dependent on latitude and that’s what we are analysing at the moment.”
More findings on the latitudinal link to the spread of the virus may also help authorities customise their response and assist in preventing its dispersion, he said.
On the situation in India, he said though the Ro was low, the number of active COVID-19 cases could surge sharply and the scenario that emerges in coming days may alter the rate for the country as well. “If the current rate of growth of coronavirus spread continues without any change, according to our projections on Wednesday (March 25), we will most likely see about 400 live infected cases (not counting people who have died or recovered from the disease by that date).
“In the worst case scenario, we will have around 900 live infected cases,” he said adding “Our projection is based on estimates of Ro which is arrived from the data. Further, the researcher said the number he has projected “is the actual number of infected people we will have on that day, and not the total number of people who have been infected from February up till now which would include people who have died or recovered subsequently.”
India, which has a mix of both tropical and sub-tropical regions thankfully has a comparatively low reproduction number of 1.7 for the coronavirus as per the study.
When asked if the ”latitude” yardstick was applied in the Indian context (vis-a-vis the virus spread in states at higher and lower latitudinal locations), he said the numbers were not adequate enough to support such a study.
On other factors that were studied that had a bearing on the spread of virus, he said: “We have looked at the dependence of Ro on the population density of these regions, initially thinking that the disease might be spreading faster in places where individuals live in higher densities.
“But much to our surprise we find that the western nations that have lower population densities have a higher Ro than more densely populated regions in China,” he said. This suggested that there were other factors than purely demographic which could be affecting the growth rate of the disease, he added.