Covid-19 likely to be more lethal during winter in cities like Mumbai, say experts

Experts believe that the cold weather with air pollution may contribute to further spread of the infection in winter, especially in overpopulated cities such as Mumbai. However, Dr Shashank Joshi, part of the state’s Covid-19 task force, overruled such theories.

With winter season less than a month away, experts have warned that Sars-CoV-2, the virus that causes Covid-19, is likely to spread faster with rise in air pollution levels. Doctors have advised extra caution as they don’t know how the virus will react to the cold weather. There is also concern of late diagnosis of infected patients as seasonal infections have symptoms similar to Covid-19 such as coughing and fever, and that it may increase fatality rate.

Citizens at a free Covid-19 testing centre in Thane on Thursday. (Praful Gangurde/ HT Photo)

Seasonal infections are caused by respiratory viruses including influenza and other types of virus that generally increase in the winter season. India Meteorological Department (IMD) classifies December, January and February as winter months.

Researchers believe that Delhi is recording a sudden rise in Covid-19 cases due to the aggravated cold weather associated with air pollution. Thus, experts believe that the cold weather with air pollution may contribute to further spread of the infection in winter, especially in overpopulated cities such as Mumbai.

“During winters, air pollutants remain more static and come closer to the ground. And as we know, Sars-CoV-2 spreads through water droplets released from the mouth. So, these infected droplets may remain suspended on the pollutants which can be as small as PM2.5 or particulate matter of size 2.5 microgram per cubic metre (ug/m3), and infect more people when they inhale it,” said Rajneesh Bhardwaj, a professor at the department of mechanical engineering, Indian Institute of Technology-Bombay (IIT-B), who has been studying how long the virus stays active on surfaces.

A recent study, Air pollution and Covid-19 mortality in the United States: Strengths and limitations of an ecological regression analysis, published by the Harvard University, shows that an increase of only 1ug/m3 in PM2.5, which are dangerous tiny pollutants in the air, is associated with an 8% increase in Covid-19 fatality rate. “A small increase in long-term exposure to PM2.5 leads to a large increase in the Covid-19 death rate,” read the report published on November 4.

Along with outdoor air pollution, experts also caution about taking precautions against indoor air pollution during the winter. Citing examples, Dr Sundeep Salvi, director of Chest Research Foundation, said mosquito coils and incense can also contribute to infecting people in rooms with poor ventilation in winters.

“As we have seen, most respiratory illnesses, such as SARS, influenza among others, spike during the months of winter as viruses tend to survive longer in a cold and dry climate. The cold air is heavier and less mobile. This makes an easy path for viruses to reach our lungs,” said Dr Salvi.

Another worrying factor is that winter reduces immunity among people which makes them more susceptible to the virus. K Srinath Reddy, president of the Public Health Foundation of India, said, “Winter aggravates respiratory ailments among people with asthma and other cardiovascular diseases. Considering Covid-19 is also a respiratory infection, such patients are more likely to contract the virus, like in Delhi.”

However, Dr Shashank Joshi, part of the state’s Covid-19 task force, overruled such theories. “When the pandemic started in March, there were speculations that the virus would wear off in summer which didn’t happen. So far, we haven’t seen any correlation between the virus and weather. As the virus is new, it is tough to say anything confirmatory,” he said.

As a precautionary measure, the Brihanmumbai Municipal Corporation (BMC) has decided to strengthen fever clinics in all wards. “Considering the symptoms of seasonal infections are similar to Covid-19, people have to be more cautious. They shouldn’t take medicines without doctor’s prescriptions which can lead to late diagnosis,” said Suresh Kakani, additional commissioner, BMC.