Updated: October 16, 2020 7:20:58 pm
After surviving the summer and the monsoon, how will SARS-CoV-2 behave in winter? While the World Health Organization (WHO) cautions that there is no reason to believe that cold weather can kill the coronavirus, the jury is still out on the precise impact of temperature on the coronavirus.
Experts agree, in fact, that most of the evidence for seasonal viruses indicate they are more active during the cooler months of the year. For instance, in many parts of the world, there is a winter seasonality for influenza, and in India and regions of similar climate, there is a monsoon peak and a smaller winter peak. Experts, however, also point out that there has been no definite trend for Covid-19 yet.
What kind of seasonality has the novel coronavirus shown so far?
Viral illnesses, especially respiratory, are supposed to thrive in colder temperatures worldwide, the obvious example being the flu virus that causes the most deaths in winters, observed Dr Shashank Joshi, Dean, Indian College of Physicians. “It has been postulated that coronavirus infections would be more prevalent during winter in the temperate geographies of the world. However, it has not shown any temperature relationship till date with seasons in tropical geographies,” Dr Joshi said.
“There does not appear to be a strong seasonality of Covid-19 yet, like there is for other respiratory diseases such as influenza,” Prof Ian Barr, Deputy Director, WHO Collaborating Centre for Reference and Research on Influenza — The Peter Doherty Institute for Infection and Immunity in Melbourne, told The Indian Express.
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“However, in places like India which have a more diverse range of seasons for influenza – at least the peak season is during the rainy/monsoon season (June to September) rather than winter. At this stage, I don’t think it matters for Covid-19. This may change when vaccines are in use. While other respiratory pathogens predominate in winter/rainy seasons, Covid-19 does not fit this pattern as yet,” Prof Barr said.
Why is winter generally associated with a spike in viral infections?
In western countries, winters can be severe and people tend to stay indoors. Hence the reasoning goes that the virus, once introduced, can circulate among people sharing the same premises.
According to virologists, however, this does not hold true in the Indian context. Dr M S Chadha, former Deputy Director of the National Institute of Virology, said people in India do not necessarily remain indoors and ventilation is better. “In northern states too people seek sunshine and so they are out,” Dr Chadha said.
In states like Maharashtra, which have been tracking H1N1 (swine flu virus) since 2009, there are usually two surges — during the monsoon, and during the winter to a lower extent. According to Maharashtra surveillance officer, Dr Pradeep Awate, the winter surge is less than half the monsoon surge.
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What have the coronavirus trends been like in other countries?
Since influenza is a winter illness, the southern hemisphere should have seen a spike in cases during their May-July winter, but that did not happen this year. In fact, even influenza cases did not spike. This is being attributed potentially to measures taken against Covid-19 — lack of interactions between people may have broken the chain of transmissions for influenza, too.
Should Indians worry?
India may get a second peak in winter, especially in the northern part of the country, said Dr Shashank Joshi.
According to Dr Gagandeep Kang, clinical scientist and vaccine researcher, there have been limited lockdowns with phase-wise opening up in the last few months, which is likely to push transmission up in winter. “But masks will drive it down. So we need to wait and see,” Dr Kang said.
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