Northerner
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There is a paradox at the heart of Sars-Cov-2 transmission that has yet to be fully explored. While it’s firmly established that the virus transmits best in winter, in common with most other respiratory viruses, the UK is currently experiencing a summer surge. There have also been major Covid-19 epidemic waves in regions such as South America and India outside winter. Why is this?
From the beginning of the pandemic, one major question was to what extent Covid would display a seasonal behaviour with higher case numbers in winter. Most respiratory viruses in circulation, including the flu and the four endemic coronaviruses contributing to “common colds”, display strong seasonal patterns, with most infections happening in winter in each hemisphere.
The mechanisms behind this seasonality are complex and not fully understood. They include the direct effect of climatic variables: enveloped RNA viruses, such as Covid-19, survive best in cold, dry air and under low UV light exposure. There is also a major host behavioural component, with humans tending to spend more time in close contact in poorly ventilated spaces during winter.
Yet, a virus being seasonal does not imply it is unable to transmit at certain times of the year, as long as conditions are otherwise favourable for its spread. To best understand this, we must consider seasonality as just one of four major factors driving transmission. The other three factors are host behaviour, viral evolution and rates of immunisation in the population, provided by prior exposure to the pathogen and/or vaccination.
www.theguardian.com
From the beginning of the pandemic, one major question was to what extent Covid would display a seasonal behaviour with higher case numbers in winter. Most respiratory viruses in circulation, including the flu and the four endemic coronaviruses contributing to “common colds”, display strong seasonal patterns, with most infections happening in winter in each hemisphere.
The mechanisms behind this seasonality are complex and not fully understood. They include the direct effect of climatic variables: enveloped RNA viruses, such as Covid-19, survive best in cold, dry air and under low UV light exposure. There is also a major host behavioural component, with humans tending to spend more time in close contact in poorly ventilated spaces during winter.
Yet, a virus being seasonal does not imply it is unable to transmit at certain times of the year, as long as conditions are otherwise favourable for its spread. To best understand this, we must consider seasonality as just one of four major factors driving transmission. The other three factors are host behaviour, viral evolution and rates of immunisation in the population, provided by prior exposure to the pathogen and/or vaccination.
If Covid-19 is a seasonal virus, why is it spreading during the summer? | Francois Balloux
Understanding seasonality can help us to work out when the pandemic is likely to be over, says Francois Balloux, the director of UCL Genetics Institute
www.theguardian.com
