Seasonal behaviour of SARS-CoV-2 found to be latitude-dependent, genetically encoded

New Delhi: Two new studies from the University of Illinois (U of I), US, have added to growing evidence supporting seasonal behaviour of the SARS-CoV-2 virus.

The first study, published in the journal Evolutionary Bioinformatics, found correlations between two years of pandemic data of COVID cases and deaths and average annual temperature and latitude across 171 countries.

"We found correlations were significant and maintained as the pandemic progressed, regardless of vaccines or the appearance of new viral variants. Results provide strong evidence that the virus is seasonal," said study author Gustavo Caetano-Anolles, professor in the Department of Crop Sciences, U of I.

"Remarkably, the seasonal effects we uncovered were not obscured by the wide range of elimination and mitigation policies applied throughout the world," said Caetano-Anolles.

Caetano-Anolles and colleagues also found the correlations between COVID-19 metrics such as new cases and deaths and total cases and deaths and temperature and latitude to strengthen during cooler months and at higher latitudes.

"We found that countries with colder average temperatures were generally correlated with higher incidence and mortality rates across the pandemic.

"This pattern suggests that future seasonal changes could lead to more predictable trends in COVID-19 cases and deaths," said co-author Nicolas Hernandez, an undergraduate researcher studying in the Department of Animal Sciences, U of I.

The researchers also evaluated relationships between Covid and environmental health, including indicators of global change, using Yale's Environmental Performance Index (EPI) and the State of Global Air report, which included scores relating to climate change, pollution emissions, household air pollution, and similar metrics for more than 150 countries globally.

Analysing patterns for March 2021, they found total COVID-19 cases and deaths to be correlated with countries' overall proactiveness towards reducing pollutant emissions, such as carbon dioxide, sulphur dioxide, and nitrogen oxides.

Higher particulate matter levels and household use of solid fuels too were found to be strongly correlated with COVID-19 cases and deaths.

In the second study, published in the journal F1000Research, Caetano-Anolles analysed sequences of more than 12 million SARS-CoV-2 genomes between the start of the pandemic and late July 2022 along with doctoral student Tre Tomaszewski in the School of Information Sciences, U of I.

They tracked the virus's genomic progression across climate zones and found a marked difference in the uptake of certain groups of presumably advantageous mutations across regions.

For example, several haplotypes - which are gene variations inherited together - were not as prominent in the tropics as they were in the northern temperate zone, especially early in the pandemic, suggesting seasonal behaviour of SARS-CoV-2 to be genetically encoded.

"Consequently, seasonal effects could be potentially manipulated through vaccine design," said Tomaszewski.