Winter is just around the corner for the Northern Hemisphere and with it come the speculations of how the pandemic might take a turn. Since most respiratory diseases including cold and flu spread quickly in winters, some experts have indicated that COVID-19 cases may also increase with a drop in temperature and humidity.
In fact, several studies have shown that SARS-CoV-2, the causative agent of COVID-19, may survive longer and hence will be able to spread more in colder climates.
However, scientists have not yet reached a consensus about the association between changes in weather and transmission of COVID-19.
A study conducted by Harvard University early this year suggested that there was no link between changing temperature and COVID-19 transmission. The World Health Organisation had said that the infection can spread at any temperature. A study done in China indicated that SARS-CoV-2 may spread quickly in summers when the temperature is around 19 degree Celsius and the relative humidity is at about 75%.
A systematic review published in the journal PLOS One indicated that warm and wet climates are not conducive to the spread of COVID-19 and that the virus would spread better in cold and drier climates. But the authors suggested that temperature and humidity are not the only variables that determine the transmission of the disease.
A study conducted in India also found that more cases of COVID-19 are seen in areas at a relatively higher altitude and colder temperatures. Several other studies have also supported the association between cold temperature and the spread of the coronavirus disease.
May not become seasonal right now
Earlier in September, a study done at the American University of Beirut in Lebanon suggested that COVID-19 may become seasonal but only after the world achieves herd immunity against this infection. This is because a major proportion of the world’s population is susceptible to the disease right now and as long as there are susceptible people, the virus will keep on spreading quickly. However, when a majority of people are immune to the disease, SARS-CoV-2 would not be able to jump hosts as effectively.
As per the study, several factors drive the spread of a viral infection. These mainly include environmental factors like temperature and humidity and host factors.
The researchers suggested that at lower temperatures, enveloped viruses like COVID-19 stay stable for long because of the improved stability in their lipid envelope.
Additionally, less humidity leads to quick evaporation of respiratory droplets which then stay in the air for longer. However, in a recent study published in the journal Physics of Fluid, the scientists indicated that microdroplets are not as effective in spreading SARS-CoV-2. Even in a non-ventilated room where an infected person has coughed, it would take a person longer than 12 minutes to be exposed to a contaminated droplet.
In the end, regardless of the effect of temperature on the disease, it is best to keep taking all the precautionary measures including social distancing, wearing face masks and maintaining hand hygiene to make sure that you and your loved ones are safe.
For more information, read our article on How COVID-19 spreads.
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