Several people, including the US president, had suggested that COVID-19 will go away in April with the heat. However in countries around the world, change in heat and humidity is having little to no effect on the spread of the COVID-19, reports Simran Sehgal.
By Simran Sehgal
With COVID-19 spreading at alarming levels across 213 countries and territories around the world, most of us were left with no choice but to hope that the deadly virus might abate as summer arrives. Many infectious diseases wax and wane with the season but coronavirus is a pandemic of much greater magnitude.
While many scientists thought the coronavirus might mimic influenza that arrives with the colder winter months, the COVID-19 virus seems to have a different pattern altogether. Unlike measles or typhoid that peak in specific seasons, coronavirus outbreak suggests no link between the spread of the virus and temperature or humidity.
In fact, if we map the prevalent trend of average temperature and number of COVID-19 cases per country, it fails to divulge any uniform pattern to support the conjecture that coronavirus is less viable in hot and humid temperatures. On the contrary, the spread has been rampant and worldwide – in cold temperatures and hot temperatures too. The deadly virus has already infected over four million people globally as of May 14.
Recent findings released by Harvard researcherswhile examining the common cold hints about how the COVID-19 virus might behave and also that summer may not save us.
The findings, published online in the journal Science, were produced by scientists from the Harvard T.H. Chan School of Public Health’s Departments of Epidemiology and of Immunology and Infectious Diseases. It suggests that in every scenario modeled, the researchers found that warm weather did not halt transmission thereby, underlining the need for extensive public health interventions to control the disease.
“This is primarily because, in the case of the common cold, a large segment of the population typically gets sick and develops immunity by spring. With SARS-CoV-2, however, enough of the population will likely remain vulnerable, allowing it to spread even if the transmission is reduced in warmer months,” it states.
The theory that weather may play a crucial role gained momentum after US President Donald Trump while citing a US Department of Homeland Security (DHS) report maintained that the chances of the coronavirus surviving in a hot and humid environment are lesser as opposed to cold and dry weather.
“There’s a theory that, in April, when it gets warm—historically, that has been able to kill the virus,” Trump said on 14 February.
However, the statement was met with a lot of criticism from researchers worldwide who have been consistently emphasising that coronavirus is a novel virus, and therefore, there’s not enough research done to rely on such inferences.
While direct conclusions based on data cannot be made, the mapping shows an increasing spread from January to April, in almost all parts of the globe with varying latitudes and temperatures.
Apparently, one intriguing study that’s yet to be published in an academic journal by scientists in China highlights that there is some sort of relationship between how deadly COVID-19 can be and the weather conditions. They looked at nearly 2,300 deaths in Wuhan, China, and compared them to the humidity, temperature, and pollution levels on the day they occurred.
The research suggests mortality rates were lower on days when the humidity levels and temperatures were higher. But this work is largely based on computer modelling, so whether it will be seen in other parts of the world, is still to be explored.
Impact of warmer weather on coronavirus in Asia
Analysis from Asian countries like India, Pakistan, Bangladesh, and Iran suggests that despite soaring temperature these nations have only witnessed a spike in the number of corona positive cases. China, the epicenter of the pandemic, is becoming warm but the country recently reported 34 new corona infections as of May 10.
The US with its cooler temperature is leading the number of corona cases in the world. But going by the analysis made by scientists at Massachusetts Institute of Technology (MIT) within the US itself, the outbreak has shown a north-south divide. “Northern (cooler) states have much higher growth rate compared to southern (warmer) states,” the scientists reported in the study.
There are multitudes of theories exploring relationships between the pathogen and the environment but for now, no one knows whether rising humidity or seasonal effect will come to the rescue.
Yet another study published in the Canadian Medical Association Journal found little or no association between latitude or temperature with epidemic growth of COVID-19, and a weak association between humidity and reduced transmission.
The researcher Peter Juni from the University of Toronto and St. Michael’s Hospital in Canada said, “Our study provides important new evidence, using global data from the COVID-19 epidemic, that the public health interventions have reduced epidemic growth.”
The results that hotter weather had no effect on the pandemic’s progression left researchers surprised.
“We had conducted a preliminary study that suggested both latitudes, and temperature could play a role. But when we repeated the study under much more rigorous conditions, we got the opposite result,” said Juni.
The researchers thus concluded that public health measures, including school closures, social distancing, and restrictions of large gatherings, have been effective in controlling the spread of the deadly virus instead of weather conditions.
Seasonality based on other coronavirus outbreaks
There was much speculation in the months of March, when the virus was in its rapid spread phase, that its growth will be slowed by the advent of the hot months of April and May. This prediction was based on the findings and behaviour of other coronaviruses.
Unlike current COVID-19, earlier coronaviruses are a family of an enveloped virus, it is coated in an oily coat of bilipid layer (which explains why washing hands with soap is encouraged so much-soap breaks the bilipid layer). The research on enveloped viruses indicates that they find it easier to survive in colder temperatures when their oily coat hardens and becomes like an impermeable mould.
Also, the seasonality aspect is based on the premise of a conclusive study in 2011 on the SARS-CoV which began its spread around the world in 2003. It was found that the virus lost its viability rapidly with increasing temperature and humidity above a certain level.
This indicates a possibility of SARS-CoV-2, COVID-19 behaving similarly as both these viruses belong to the coronavirus family but it is important to understand that the new virus has emerged 17 years later which gives it enough time to mutate and change its characteristics.
In fact, SARS-CoV-2 has been found to be more closely related to bat coronaviruses than SARS-CoV.
Besides, the World Health Organisation (WHO) as a part of their myth-buster series has confirmed time and again that COVID-19 can be transmitted in hot and humid climates. And that any kind of exposure to sun and temperatures higher than 25 degrees will not kill the virus. Our only weapon against this fight is regular hand washing or hand sanitizing and maintaining social distancing.
In other words, the soaring temperature will provide no respite from COVID-19, and that each country will have to design their own response plan to win this global war against the coronavirus.
