"Colds are more common in the winter, but it's almost certainly correlation, not causation, says John Tregoning, a professor in vaccine immunology at Imperial College London. One marginal factor is that UV light can kill viruses. Sneezing outside in the summer, for example, may expose viral droplets to sunlight, which can deactivate the virus, while faster evaporation causes it to desiccate. But the main driver is behavioural: in colder months, we spend more time indoors with poorer ventilation and in closer contact with others."
"Data from the Covid-19 pandemic shows how much human contact matters: many other viruses largely disappeared during lockdown because people weren't interacting. One strain of flu even became extinct due to lack of spread. That said, extreme cold can affect your susceptibility to viruses. If you were cold all the time, losing calories and exhausted, you'd be more prone to infection, Tregoning says."
Colds peak in winter mainly due to behavioural factors: increased indoor time, poorer ventilation, and closer contact among people. UV light and sunlight can reduce viral survival by deactivating droplets and speeding evaporation, offering a minor protective effect outdoors in summer. Different respiratory viruses peak at different times: rhinovirus surges when children return to school; RSV tends to peak around the new year. Pandemic-era restrictions showed that reduced human interaction dramatically cut transmission, even causing one flu strain to disappear. Extreme, prolonged cold can weaken host resilience, while vaccines against flu and RSV offer the most effective protection.
Read at www.theguardian.com
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