Image: John Hopkins Medicine

Lower Humidity Levels May Increase Coronavirus Cases By 6 Percent

A new study conducted by researchers from the University of Sydney and the  Fudan University School of Public Health in Shanghai looks at the association between coronavirus cases and the changes in the weather including lower humidity levels and concludes that less humid weather may increase the risk of coronavirus spread.

The research, which originally started in the early days of the coronavirus pandemic, highlights that a mere one percent decrease in humidity levels led to a six percent increase in coronavirus cases which were acquired locally. Till now, it is the first peer-reviewed study that looks at the potential connection between climate and coronavirus cases and transmission.

According to Professor Michael Ward, who is the leading investigator and an epidemiologist in the Sydney School of Veterinary Science at the University of Sydney, the findings of the study show that the coronavirus infection could be a seasonal disease.

He added that the infection is more likely to spread in people during colder months. Therefore, health experts should be aware that the beginning of winters could mean the starting of more coronavirus cases. These findings appear in the journal Transboundary and Emerging Diseases.

Though the research accentuates the relationship of lower humidity levels in the southern hemisphere and a rise in coronavirus cases, the team of researchers agrees that further investigation is needed to estimate the extent of how changes in the weather can affect the novel coronavirus and why exactly does humidity affect its transmission.

Studies conducted previously on similar infections caused by other coronaviruses including the Middle Eastern Respiratory Syndrome or MERS and Severe Acute Respiratory Syndrome or SARS-CoV showed links between climate changes and a higher number of cases.

More recently, a small study conducted in China also identified an association between the transmission of the SARS-CoV-2 and changes in the levels of humidity as well as in the temperature.

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Professor Ward explained that at the beginning of the coronavirus pandemic, the weather was cold in North America, China, and Europe. However, in Australia, the climate is very different in comparison.

Therefore, Professor Ward along with his team was interested in seeing whether the link between the weather in Australia and coronavirus transmission was also different than in Europe or China.

“When it comes to climate, we found that lower humidity levels are the main driver here, rather than colder temperatures,” Professor Ward stated in the paper.

“It means we may see an increased risk in winter here when we have a drop in humidity. But in the northern hemisphere, in areas with lower humidity or during periods when the humidity drops, there might be a risk even during the summer months. So vigilance must be maintained.” He added.

The humidity levels primarily affect coronavirus transmission because they impact the aerosol particles that are released in the air when an infected person sneezes or coughs. With lower humidity levels, the particles are smaller in size as the air is dry.

Smaller size allows the aerosol particles to stay in the air for a much longer period of time and infect more people. On the other hand, when humidity levels are higher, the particles are larger and they settle down on the ground.

These findings explain why there may be a spike in coronavirus cases in Australia during the colder months. The humidity levels are lowest in August.

Even though the country has relatively controlled coronavirus cases, dry air could make the coronavirus spread quicker, which is why people should continue to follow all precautionary measures in order to avoid the infection.