COVID-19 as a true seasonal low-temperature infection, similar to influenza: study results
By NewsDesk @ bactiman63
A new study conducted by the Barcelona Institute for Global Health (ISGlobal), an institution supported by the “la Caixa” Foundation, provides strong evidence that COVID-19 is a seasonal infection associated with low temperatures and humidity, much like the seasonal flu. The results, published in Computer science of nature, also support the significant contribution of airborne transmission of SARS-CoV-2 and the need to shift to measures that promote “air hygiene”.
A key question regarding SARS-CoV-2 is whether it behaves or will behave like a seasonal virus like the flu, or whether it will also be transmitted at any time of the year. A first theoretical modeling study suggested that climate was not a factor in the transmission of COVID-19, given the high number of susceptible individuals without immunity to the virus. However, some observations suggest that the initial spread of COVID-19 in China occurred at a latitude between 30 and 50.o N, with low humidity and low temperatures (between 5o and 11 o VS).
“The question of whether COVID-19 is a true seasonal disease is becoming increasingly central, with implications for determining effective intervention measures,” explains Xavier Rodó, director of the Climate and Health program at ISGlobal and study coordinator. To answer this question, Rodó and his team first analyzed the association of temperature and humidity in the initial phase of the spread of SARS-CoV-2 in 162 countries on five continents, before the implementation of changes in human behavior and public health policies. The results show a negative relationship between transmission rate (R0) and both temperature and humidity on a global scale: higher transmission rates were associated with lower temperatures and humidity.
The team then analyzed how this association between climate and disease has evolved over time and whether it is consistent across different geographic scales. For this, they used a statistical method that was specifically developed to identify similar variation patterns (i.e. a pattern recognition tool) at different time windows. Again, they found a strong negative association for the short periods of time between disease (number of cases) and climate (temperature and humidity), with consistent patterns during the first, second and third waves of the pandemic at different spatial scales: worldwide, from countries, up to individual regions within heavily affected countries (Lombardy, Thuringia and Catalonia) and even at city level (Barcelona).
The first epidemic waves decreased as temperature and humidity increased, and the second wave increased as temperatures and humidity decreased. However, this model was broken during the summer on all continents. “This could be explained by several factors, including mass gatherings of young people, tourism and air conditioning, among others,” explains Alexandre fontal, researcher at ISGlobal and first author of the study.
When fitting the model to analyze transient correlations at all scales in countries in the southern hemisphere, where the virus arrived later, the same negative correlation was observed. The climatic effects were most evident at temperatures between 12o and 18oC and humidity between 4 and 12 g / m3, although the authors caution that these ranges are still indicative, given the short recordings available.
Finally, using an epidemiological model, the research team showed that incorporating temperature into the transmission rate works best to predict the rise and fall of different waves, especially the first and third in Europe. “Overall, our results support the view of COVID-19 as a true seasonal low-temperature infection, similar to influenza and more benign circulating coronaviruses,” says Rodó.
This seasonality could contribute significantly to the transmission of SARS-CoV-2, as low humidity conditions have been shown to reduce the size of aerosols and thus increase airborne transmission of seasonal viruses such as influenza. “This link justifies a emphasis on “air hygiene” thanks to better interior ventilation because the aerosols are able to persist in suspension for a longer time ”, explains Rodó, and underlines the need to include meteorological parameters in the assessment and planning of control measures.