Will summer heat bring coronavirus to a halt? Here is what we know so far

Will the onset of Indian summer arrest the march of the novel coronavirus? This question has been asked repeatedly in the past two weeks as the viral respiratory disease, which originated in China in December, took a firm hold in several parts of India.

Officially known as Covid-19, coronavirus has been declared a pandemic by the World Health Organisation because of its rapid spread to over 100 countries around the world, infecting more than 1.2 lakh people and killing over 4,700. In India, the virus has now infected at least 77 people across 12 states, including Delhi, Kerala, Uttar Pradesh and Maharashtra.

As the Central government suspended all visas to India and states like Delhi and Karnataka announced the closure of schools and colleges for the next few weeks, panic around the spread of coronavirus has led many people to cling onto a common belief for hope: the belief that in warmer weather, viruses die out on their own.

In general, the spread of virus-based respiratory illnesses does tend to reduce with the rise in temperatures during summer. There has been global speculation on whether coronavirus, too, will stop transmitting rapidly once summer begins.

But can summer heat really bring the coronavirus pandemic to a halt?

On Thursday evening, India’s Union Health Ministry answered this question with a short and clear response: even though flus are not usually common in summer, there is no evidence or study to suggest that high temperature kills coronavirus.

Across the world, doctors and scientists have emphasised this very point: even though viruses are not expected to survive in higher temperatures, there is still a lot that we do not know about Covid-19, and we cannot afford to make assumptions.

Important myth-busting

The hope that the novel coronavirus will dissipate in summer rests on two common assumptions. One is that the common cold, caused by other types of coronaviruses, is typically seasonal and does not get transmitted much in summers. The second is that in 2003, the severe acute respiratory syndrome virus, or SARS, died away on its own in warmer weather. (Covid-19 is a type of SARS that shares 90% of its DNA with SARS).

According to scientists, both these assumptions are myths.

“SARS did not die of natural causes,” writes March Lipsitch, an epidemiology professor at the Harvard TH Chan School of Public Health in Boston. “It was killed by extremely intense public health interventions in mainland Chinese cities, Hong Kong, Vietnam, Thailand, Canada and elsewhere.”

These interventions included social distancing and quarantining people who had come in contact with SARS infected patients. In fact, Lipsitch points out that Canada saw a resurgence of SARS when it relaxed these precautionary measures.

Besides, the Middle East respiratory syndrome or MERS – also a type of coronavirus – is transmitted mainly in hot countries.

Old versus new viruses

The other assumption – that the coronaviruses that cause what we know as the “common cold” are seasonal – is true only to a limited extent. This is because viruses that have been around in the world for a longer period of time cannot spread as easily as viruses that are new to humans.

Certain viruses, like the influenza virus, thrive in cooler, drier air, making them more widespread during winters. But even then, their ability to infect people depends on how immune people are to them. In the case of older viruses that have been infecting human populations for several years, most people are now immune to them, and the viruses can transmit only among those who are not.

“In simple terms, viruses that have been around for a long time can…spread through the population only when the conditions are the most favourable, in this case in winter,” writes Lipsitch.

In contrast, humans have not yet developed an immunity to the new Covid-19 virus, making it easy for the virus to spread irrespective of seasons or weather conditions.

Too early to predict

At this point, the general consensus among experts is that Covid-19 could be transmitted less rapidly in summer months, but the change may not be significant enough to control the disease.

More importantly, experts agree that we simply do not have credible scientific data so far to conclusively claim any connection between Covid-19 and the heat.

For instance, Dr V Ramasubramanian, a consultant on infectious diseases at Apollo Hospitals, claims that sunlight may inhibit the growth, viability and stability of the virus, but the heat is unlikely to deter human-to-human transmission of the virus. “We know that it survives in the human body at 37 degrees Celsius,” Ramasubramanian said in an interview with The Hindu. “The only probability is that it may not survive in the outside environment.”

The central government also made its stand clear on the subject. At a special Covid-19 press conference held on Thursday, a Ministry of Health spokesperson emphasised that a lot of things about the coronavirus are still unknown, and no information about whether it will survive in higher temperatures has been confirmed yet, since the virus was only discovered at the end of December 2019.

“Intuitive thinking tends to tell you that flu is not a common manifestation in summer,” said Dr Raman Gangakhedkar, the head of epidemiology and communicable diseases at the central government’s Indian Council of Medical Research. “But since we don’t have any evidence, it would be better to have a cautious approach. This should not make us complacent in terms of adopting safer practices.”