Researchers from the University of Illinois stated in their study that coronavirus pandemic may be seasonal.
The study, published in Evolutionary Bioinformatics, Illinois, showed Covid-19 cases and mortality rates, among other epidemiological metrics, are significantly correlated with temperature and latitude across 221 countries.
“One conclusion is that the disease may be seasonal, like the flu. This is very relevant to what we should expect from now on after the vaccine controls these first waves of Covid-19,” says Gustavo Caetano-Anollés, affiliate of the Carl R Woese Institute for Genomic Biology at Illinois, and senior author on the paper.
For the study, the researchers downloaded relevant epidemiological data from 221 countries, along with their latitude, longitude, and average temperature. They pulled the data from April 15, 2020, because the seasonal temperature variation is at its maximum across the globe during that time.
That date also coincided with a time during the early pandemic when Covid-19 infections were peaking everywhere.
The research team then used statistical methods to test if epidemiological variables were correlated with temperature, latitude, and longitude. The expectation was that warmer countries closer to the equator would be the least affected by the disease.
“Indeed, our worldwide epidemiological analysis showed a statistically significant correlation between temperature and incidence, mortality, recovery cases, and active cases. The same tendency was found with latitude, but not with longitude, as we expected,” Caetano-Anollés said.
While temperature and latitude were unmistakably correlated with Covid-19 cases, the researchers also pointed out climate is only one factor driving seasonal Covid-19 incidence worldwide.
They accounted for other factors by standardizing raw epidemiological data into disease rates per capita. They also assigned each country a risk index reflecting public health preparedness and incidence of co-morbidities in the population.
The idea was that if the disease was surging in countries with inadequate resources or higher-than-average rates of diabetes, obesity, or old age, the risk index would appear more important in the analysis than temperature. However, that was not the case. The index did not correlate with the disease metrics at all.
“Our results suggest the virus is changing at its own pace, and mutations are affected by factors other than temperature or latitude. We don’t know exactly what those factors are, but we can now say seasonal effects are independent of the genetic makeup of the virus,” Caetano-Anollés says.
The researchers also noted that the body’s own immune system could be partially responsible for the pattern of seasonality. They believe that it is too soon to say how seasonality and our immune systems interact in the case of Covid-19.