Study finds ‘robust’ evidence that COVID-19 is a seasonal infection

COVID-19 can be a seasonal infection linked to low temperatures and humidity, much like seasonal flu, according to “robust” new evidence found by researchers.

The study, recently published in the journal Nature Computational Science, also supports the significant contribution of airborne transmission of SARS-CoV-2 and the need to shift to measures that promote “air hygiene.” A research team led by the Barcelona Institute for Global Health (ISGlobal), Spain, noted that a key question regarding SARS-CoV-2 is whether it behaves or will behave like a seasonal virus like flu, or whether it will also be transmitted at any time of the year.

A first theoretical modeling study suggested that the climate was not a transmission factor for 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 degrees N, with low humidity levels and low temperatures between 5 degrees and 11 degrees Celsius.

“The question of whether COVID-19 is a true seasonal disease is becoming increasingly central, with implications for determining effective intervention measures,” said Xavier Rodo, director of the Climate and Health program at ISGlobal and coordinator of the study.

The researchers 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 changes in human behavior and health policies public are in place.

The results show a negative relationship between transmission rate (R0) and temperature and humidity globally, the researchers said.

Higher transmission rates were associated with lower temperatures and humidity, they said.

The researchers then analyzed how this association between climate and disease evolved over time and whether it was consistent across different geographic scales.

They used a statistical method that was specifically developed to identify similar patterns of variation at different time windows.

The team found a strong negative association for the short time windows between the number of cases and temperature and humidity.

The patterns were consistent during the first, second and third waves of the pandemic at different spatial scales: worldwide, within countries, down to individual regions of the most affected countries and even at the city level.

The first epidemic waves decreased as temperature and humidity increased, and the second wave increased as temperatures and humidity decreased, the researchers said.

However, this pattern was broken over the summer on all continents, they said.

“This could be explained by several factors, including mass gatherings of young people, tourism and air conditioning, among others,” said Alejandro 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.

Climatic effects were most evident at temperatures between 12 degrees and 18 degrees Celsius and humidity levels between 4 and 12 grams per cubic meter (g / m3).

However, the study authors cautioned that these ranges are still indicative, given the short recordings available.

Using an epidemiological model, the researcher 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,” Rodo said.

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 the emphasis on ‘air hygiene’ through improved indoor ventilation, as aerosols are able to persist in suspension for longer,” said Rodo.

The study highlights the need to include meteorological parameters in the assessment and planning of control measures.

(This story was not edited by Devdiscourse staff and is auto-generated from a syndicated feed.)

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