Humidity is Closely Related to the Covid-19 Epidemic

A study conducted at the early stage of the COVID-19 epidemic in New South Wales found that lower air humidity was associated with an increase in positive cases – a decrease of 1% in humidity would increase the number of cases by 6%. This study was recently published in the journal of Transboundary and Emerging Diseases.

This study, led by Professor Michael Ward, an epidemiologist from the School of Veterinary Medicine of the University of Sydney, and two researchers from the School of Public Health of Fudan University in Shanghai, a cooperative institution of the University of Sydney, is the first peer reviewed study in the southern hemisphere to explore the relationship between climate and COVID-19.

“COVID-19 is probably a seasonal disease that will recur in the period of low humidity. What we need to think about is that winter may be the period when the epidemic will recur,” said Professor Ward. However, further research is needed to determine the specific relationship between humidity and COVID-19, and to what extent humidity affects COVID-19 cases.

Previous studies have found a link between climate and SARS CoV cases in China and MERS CoV cases in Saudi Arabia, while a recent study on the COVID-19 in China found a link between disease transmission and daily temperature and relative humidity.

“The outbreaks in China, Europe and North America all occurred in winter, so we want to see whether the relationship between COVID-19 cases and climate will be different in late summer and early autumn in Australia,” said Professor Ward.

“We found that low humidity is the main driving factor in the climate impact, rather than low temperature. This means that when the humidity in the southern hemisphere decreases in winter, the risk of epidemic situation will increase accordingly. However, in the northern hemisphere, there are high risks in areas with low humidity or during periods of humidity decline, even in summer. So, we must be vigilant.”

——Professor Michael Ward, School of Veterinary Medicine, University of Sydney

Why humidity is the main influencing factor

Professor Ward mentioned that humidity has an impact on the spread of viruses in the air. “When the humidity is low, the air is dry, which will make the aerosol particles smaller. When you sneeze or cough, these smaller aerosols with infectious virus will stay in the air for a long time, which will increase the exposure time of other people. On the contrary, when the air is wet, the aerosol will be larger and heavier, and will fall to the ground faster.”

Research method

Professor Ward and his team studied a total of 749 cases in Greater Sydney, New South Wales from February 26 to March 31, matched the patient’s postal code with the local recent weather, and included the rainfall, temperature and humidity from January to March 2020 into the study scope.

The study found that low humidity was negatively correlated with the number of cases. If the relative humidity decreased by 1%, the number of cases increased by 6%. “This means that we need to deal with dry winter more carefully,” said Professor Ward.

Must be continuously detected and tracked

“Although the epidemic situation has improved, we still need to remain vigilant. The public health system needs to pay attention to the potential risks implied by low humidity. Continuous detection and tracking are crucial,” said Professor Ward. “It should be noted that this study only covers the summer cases in Sydney and its surrounding areas, so it is necessary to continue the study in the next few months. For example, in winter, lower temperature may also become one of the influencing factors.”

Preair suggests that in autumn and winter, whether you are indoors or outdoors, you should wear masks scientifically. Under normal wearing conditions, the mask should be replaced every 4 hours or so. If it is wet, it should be replaced immediately. When changing the mask, choose a place with ventilation and no crowd. After changing the mask, carry out hand disinfection. Timely cleaning of hands can remove dirt and bacteria from hands, prevent contact infection and reduce the spread of infectious diseases. Advocate frequent window opening and ventilation, and keep the indoor environment clean and ventilated.