Second wave of COVID-19 pandemic was driven by the weather

Many people blame the second wave of the coronavirus pandemic on a lack of safety precautions and social distancing measures, but a new study suggests that a second outbreak of COVID-19 was inevitable due to the weather. 

Experts at the American Institute of Physics report that specific weather parameters – including temperature, relative humidity, and wind speed – can be used to predict the second wave of a pandemic.

In a previous study, the AIP team set out to understand how various components of the climate influence the spread of the coronavirus. 

The researchers analyzed the effects of temperature, humidity, and wind speed on the aerosol droplet cloud and virus viability. They found that evaporation is a critical factor in virus transmission.

“We found high temperature and low relative humidity lead to high evaporation rates of saliva-contaminated droplets, thus significantly reducing the virus viability,” said study co-author Talib Dbouk.

The experts determined that the concentration of the aerosol droplet cloud, as well as the distance it travels, can persist at high temperatures when the relative humidity is high. The study also revealed that wind speed plays a role in the spread of viruses.

The results of the study predicted a second wave of the pandemic in the fall and winter seasons, when low temperatures and high wind speeds would increase airborne virus survival and transmission.

In the current study, Dbouk and co-author Dimitris Drikakis emphasize that climate effects must be accounted for in models that are used to predict the behavior of an epidemic. 

Current epidemiological models typically rely on only two basic parameters, transmission rate and recovery rate. While these two rates are often assumed to be constants, the researchers say this is not the case. They have developed a new weather-dependent variable called the Airborne Infection Rate index.

When the experts applied the AIR index to models of Paris, New York City, and Rio de Janeiro, the timing of the second outbreak in each city was accurately predicted. 

Furthermore, the data showed that the virus behaved very differently in Rio de Janeiro compared to Paris and New York, which can be explained by seasonal variations in the northern and southern hemispheres.

The study authors stress the importance of accounting for these seasonal variables when designing safety measures.

“We propose that epidemiological models must incorporate climate effects through the AIR index,” said Drikakis. “National lockdowns or large-scale lockdowns should not be based on short-term prediction models that exclude the effects of weather seasonality.”

“In pandemics, where massive and effective vaccination is not available, the government planning should be longer-term by considering weather effects and design the public health and safety guidelines accordingly,” said Dbouk. “This could help avoid reactive responses in terms of strict lockdowns that adversely affect all aspects of life and the global economy.”

Drikakis and Dbouk expect another improvement in infection numbers as temperatures rise and humidity falls. Regardless, they note that masks should still be worn and social distancing guidelines should continue to be followed. 

The study is published in the journal Physics of Fluids.

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By Chrissy Sexton, Earth.com Staff Writer