Robust Evidence Says That Covid-19 Is A Seasonal Infection: Study

Is there a relationship between COVID-19 and weather, is a question that has had continuous discussions and varied conclusions. But, recently, a study by the Barcelona Institute for Global Health (ISGlobal) has provided robust evidence that COVID-19 is a seasonal infection. Let us know more about it.

A new study led by the Barcelona Institute for Global Health (ISGlobal), an institution supported by “la Caixa” Foundation, provides robust evidence that COVID-19 is a seasonal infection linked to low temperatures and humidity, much like seasonal influenza. The results, published in Nature Computational Science, also support the considerable contribution of airborne SARS-CoV-2 transmission and the need to shift to measures that promote “air hygiene”.

A key question regarding SARS-CoV-2 is whether it is behaving, or will behave, as a seasonal virus like influenza, or whether it will be equally transmitted during any time of the year. A first theoretical modelling study suggested that climate was not a driver in COVID-19 transmission, given the high number of susceptible individuals with no immunity to the virus.

“The question of whether COVID-19 is a genuine seasonal disease becomes increasingly central, with implications for determining effective intervention measures,” explains Xavier Rodó, director of the Climate and Health programme at ISGlobal and coordinator of the study. To answer this question, Rodó and his team first analysed the association of temperature and humidity in the initial phase of SARS-CoV-2 spread in 162 countries across five continents, before changes in human behaviour and public health policies were put into place.

The team then analysed how this association between climate and disease evolved over time, and whether it was consistent at different geographical scales. For this, they used a statistical method that was specifically developed to identify similar patterns of variation (i.e. a pattern-recognition tool) at different windows of time.

The first epidemic waves waned as temperature and humidity rose, and the second wave rose as temperatures and humidity fell. However, this pattern was broken during the summertime on all continents. “This could be explained by several factors, including mass gatherings of young people, tourism, and air conditioning, among others,” explains Alejandro Fontal, a researcher at ISGlobal and first author of the study.

Finally, using an epidemiological model, the research team showed that incorporating temperature into the transmission rate works better for predicting the rise and fall of the different waves, particularly the first and third ones in Europe. “Altogether, our findings support the view of COVID-19 as a true seasonal low-temperature infection, similar to influenza and to the more benign circulating coronaviruses,” says Rodó.

This seasonality could contribute importantly to the transmission of SARS-CoV-2, since low humidity conditions have been shown to reduce the size of aerosols, and thereby increase airborne transmission of seasonal viruses such as influenza.