Recent study has suggested that low humidity increases COVID risk

by Vivien Mah    

Dry leaf to indicate low humidity

As we are currently in the third week of the second wave of the epidemic here in Victoria, we think that it would be a good idea to push more information regarding the disease, and what can be done to combat it. 

In a recent study performed by Professor Michael Ward, an epidemiologist at the University of Sydney showed that dry air could prompt the further spread of the disease. The initial study, which was performed in June, focused on the Greater Sydney area during the early stages of the COVID-19 epidemic, and found that there was an association between lower humidity and increases in community transmission. The second, and more recent study has again noticed a correlation between humidity and SARS-CoV-2 transmission- a very daunting update, to say the least.      

Low humidity and COVID-19

The studies found that for an estimated 1% decrease in relative humidity, there is a potential increase in COVID-19 cases- a 7-8% increase.  low humidity (also defined as “dry air”) 

According to the study, the estimate is roughly a two-fold increase in COVID-19 notifications for a 10% drop in relative humidity. 

“Dry air appears to favour the spread of COVID-19, meaning time and place become important,” Professor Ward said. “Accumulating evidence shows that climate is a factor in COVID-19 spread, raising the prospect of seasonal disease outbreaks.”


Why humidity matters

“When the humidity is lower, the air is drier and it makes the aerosols smaller,” said Professor Ward, mentioning that aerosols are smaller than droplets, in terms of size. “When you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people. When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker.”

“This suggests the need for people to wear a mask, both to prevent infectious aerosols escaping into the air in the case of an infectious individual, and exposure to infectious aerosols in the case of an uninfected individual,” Professor Ward said.


Key findings

  • Additional evidence from the Sydney COVID-19 epidemic has confirmed cases to be associated with humidity
  • Reduced humidity was found in several different regions of Sydney to be consistently linked to increased cases
  • The same link was not found for other weather factors - rainfall, temperature or wind
  • Climatic conditions conducive to the spread of COVID-19 present a challenge to public health.

Further studies on humidity for the remainder of the year are needed to determine how the humidity relationship works and the extent to which it drives COVID-19 case notification rates.


Disclaimer: The information provided in this article is for general reference only. Please seek advice from professionals according to your needs.