As data accumulate on Covid19 cases in north Bengal and Sikkim as in the rest of the country, researchers have observed patterns of peaks and valleys that repeat on a near-weekly basis in the region. But understanding what is driving those patterns has remained an open question as much for the experts as for the general public here.

According to Dr Sharmistha Bhattacherjee, Head of the Department of Community Medicine at the North Bengal Medical College and Hospital, the oscillations in the rate of infections every week arise, in all probability, from variations in testing practices and data reporting.

“The periodic highs and lows in the incidence data are mainly due to daily differences in the number of suspected patients turning up for tests at the various testing centres in a particular area. Some people may go for a test within a few days of showing Covid-like symptoms, while others may prefer to stay in home isolation for a few days more and then go for a test if symptoms persist,” she said.

The noted community medicine expert feels that the peculiar weekly trend of highs and lows in infection rates in north Bengal could also arise from societal practices. “An increase in social gatherings on the weekends may be a major factor, though the time from exposure to the virus to showing symptoms can range from four to 14 days. The weekend interactions can significantly influence outcomes and these factors may contribute remarkably to the repeated patterns of the virus’s waxing and waning spread,” she cautioned.

A senior professor of the Department of Biotechnology, University of North Bengal, Dr Ranadhir Chakraborty, attributed the periodic oscillations in daily reported infections in Sikkim and North Bengal, especially in Darjeeling and Jalpaiguri districts, to the fluctuating populations in these areas. “The fluctuations in the daily Covid case count is almost directly proportional to the increase and decrease in the floating population in our region, that is, the group of people who come to stay here for a certain period of time and for various reasons, but are not generally considered part of the official census count,” said Dr Chakrabortym who was part of an international team which mapped a total of 71,703 genomes of the coronavirus till August 2020.

The senior microbiologist maintained that the easing of restrictions on July 1 by the West Bengal government could also have contributed to the fluctuating trend in fresh coronavirus cases in north Bengal. “After reaching a staggeringly high peak of 633 cases on May 18, the second wave in Darjeeling district began to plummet steadily and for the first time in three months, the daily case count dropped below the 100 mark on July 3. But after reaching a plateau about three weeks ago, the cases are fluctuating almost every day now,” he
pointed out.

According to Dr Chakraborty, as long as there were infected people in our region and people here did not follow the Covid protocol to break the chain of infection, the oscillations in the rate of infections every week, due to fluctuations in the number of daily cases, would always be observed even if the number of cases dropped. “A close study of the pattern of infections in north Bengal, Sikkim and the north-eastern states would reveal that the growth sequence of the number of new confirmed cases per day has a significant cluster of fluctuations, which portend the third wave of the pandemic which most epidemiologists now feel may be coming soon through this region. We must remember that the longer the virus persists in a population, the more opportunities it will have to accumulate mutations that could allow it to evade the human immune system,” he warned.

Dr Kaushik Bhattacharya, a noted surgeon of north Bengal, who agreed with Dr Chakraborty, said that plotting the rolling three-day average of cases in Darjeeling district showed that the graph rises and falls every week. “The most important aspect of the weekly modulation in our district is that it is not very universal in nature the frequency of the weekly troughs and peaks do not match with the weekly troughs and crests of most places across the globe. This trend is consistent and is more pronounced in our district mainly because the number of cases here is proportionately high.

It means that the virus is still circulating in our population mainly because of the patchy availability of vaccines, vaccine hesitancy and a lack of herd immunity. In such a scenario, strict and effective measures should be taken immediately to ensure that people adhere to the standard operating procedures properly,” Dr Bhattacharya said.