COVID-19 is seasonal and is best transmitted with low temperature and humidity

COVID-19 is a seasonal disease and its transmission is associated with low temperatures and humidity, as occurs with the flu and other colds caused by coronavirus, according to a study by the Barcelona Institute for Global Health (ISGlobal).

The study, published in the journal “Nature Computational Science”, Also highlights the“considerable“Contribution of aerosol transmission and the need to adopt measures that promote the”air hygiene”.

Scientists initially ruled out that SARS-CoV-2 behaved like a seasonal virus similar to the flu virus because it appeared to be transmitted with the same intensity throughout the year.

A first study with theoretical models suggested that climate was not an important factor, given the large number of susceptible people without prior immunity against the virus.

However, some observations suggested that the initial spread of the virus in China occurred at latitude between 30 and 50 degrees north, with low humidity levels and cold temperatures of between 5 and 11 degrees centigrade.

“The question of whether COVID-19 is a truly seasonal disease becomes increasingly important to implement effective interventions”, Said the director of the ISGlobal Climate and Health program and coordinator of the study, Xavier Rodó.

He recalled that ISGlobal developed “one of the only two predictive computational models that have been applied in many countries, with very positive results in most of them”.

Researchers at ISGlobal, a center promoted by the La Caixa Foundation, have analyzed the association of temperature and humidity in the initial phase of the spread of the virus in 162 countries, have established a correlation with the transmission rate of SARS-CoV-2 and have found that higher transmission rates are associated with lower temperatures and lower humidity.

They have also analyzed the evolution of this association between climate and disease over time, and whether it was consistent at different geographical scales using a statistical method specifically designed to identify similar patterns of variation, that is, a pattern recognition tool in different windows of time.

These data, with consistent patterns during the first, second and third waves of the pandemic and referring to countries and regions highly affected by the virus, such as Lombardy (Italy), Thuringia (Germany), Catalonia (Spain), and even at the level of cities, like Barcelona.

Thus, they have verified that the first pandemic waves diminished with increasing temperature and humidity, and that the second wave increased with decreasing temperature and humidity. However, this pattern was broken during the summer on all continents.

“This could be due to several factors, including massive concentrations of young people, tourism and air conditioning, among others.”, Justified ISGlobal researcher Alejandro Fontal.

When they studied the correlations with the climate in the countries of the southern hemisphere, where the virus arrived later, they observed the same pattern of behavior.

The effects of climate were most evident at temperatures between 12 ° and 18 ° Celsius and humidity levels between 4 and 12 g / m3, although the researchers have warned that these are indicative ranges, due to the limited time of records.

Finally, using an epidemiological model, the study shows that incorporating temperature into the transmission rate works better to predict the rise and fall of different waves, particularly the first and third in Europe.

“Our combined results support the idea that COVID-19 is a truly seasonal infection, similar to the flu and the other common cold coronaviruses.”, Concluded Rodó.

This seasonality, according to the researchers, could contribute to the transmission of SARS-CoV-2, since low humidity conditions reduce the size of aerosols and therefore increase the airborne transmission of seasonal viruses such as influenza.

“This association justifies the need to sanitize the air through better ventilation of the interior spaces, since the aerosols can remain suspended for longer.”, According to Rodó, who underlined the need to include meteorological parameters in the planning and evaluation of control measures.