Everything from seasonal temperatures differences to changes in human behavior can impact the way a virus spreads, so what does that mean for the future of Covid-19?
Well according to one recent publication, Covid-19 could become a seasonal virus like the flu.
The report, published in Frontiers in Public Health, examined previous endemic respiratory viruses like the flu and other coronaviruses to try and see what might happen with Covid-19.
But it’s not as simple as it might sound.
There are at least four pre-existing coronaviruses that are seasonal, but it’s still unclear why some are seasonal and others aren’t.
“Not all viruses show higher peaks of infection in the winter: it depends on their route of transmission. For respiratory viruses, which do peak in winter, an important factor is the ability of the actual virus to resist environmental stresses. These include heat, humidity and UV light,” explained Mike Skinner, a virologist based at Imperial College London, in an interview with BBC Science Focus Magazine.
Additionally, human behavior often plays a large role in why a virus might peak in winter months.
“In winter we tend to be much more closely crowded together, and we create higher relative humidities in our homes and work places because we remain inside and turn up the heating,” added Skinner.
So to determine if a virus is more influenced by social behaviour or temperature can be difficult. In the case of Covid-19 both could be equally impactful.
But in the most recent study, the researchers looked at the how previous endemic respiratory viruses have evolved and hypothesize that Covid-19 will likely become seasonal in countries that experience winter.
“Even though tropical regions are suffering from a high Covid-19 pandemic burden, virus transmission has been more aggressive in the temperate regions where winter is prevailing. This indicates that cold and dry conditions might promote SARS-CoV-2 infections,” the researchers explained in their paper.
“Based on our previous knowledge about the seasonality of respiratory viruses and the recent studies about stability and transmission of SARS-CoV-2, we speculate that the virus might mimic the other respiratory viruses and wane during summer due to warmer and more humid weather.”
But early research has shown that temperature has very little to do with how the coronavirus spreads.
One study looked at Covid-19 cases in 144 separate places (various provinces, states and countries) during March when the pandemic was quickly spreading around the globe.
The researchers collected data about temperatures, humidity and latitude, as well as public health measures introduced to control the virus, between March 7 to 13. Then they waited for two-week so that new infections could develop, and be diagnosed and reported – at the growing case count for the period of March 21 to 27 and the results showed the virus didn’t depend on temperature but rather the public health measures that were implemented like social distancing and school closures.
Although, the results could be due to the fact that most people don’t have immunity to it.
And lack of immunity means that Covid-19’s transmission rate (R0) is way higher than other seasonal viruses, so the researchers argue that Covid-19 won’t become a seasonal virus until herd immunity is reached.
“Covid-19 is here to stay and it will continue to cause outbreaks year-round until herd immunity is achieved,” said study author Hassan Zaraket, of the American University of Beirut in Lebanon, in the release.
“But, once herd immunity is attained through natural infections and vaccinations, the R0 should drop substantially, making the virus more susceptible to seasonal factors.”
Even still, many experts point out that Covid-19 hasn’t acted like any of the other coronaviruses so it’s impossible to say whether it will behave like them. And despite the growing body of scientific research, we still don’t know a lot about the virus and immunity.
And while many are holding out hope for a vaccine there’s still a lot of questions about how long it will provide protection. Additionally, with the recent news that a coronavirus vaccine won’t be available to everyone until 2024, herd immunity seems like a pipe dream.
“This remains a novel virus and despite the fast-growing body of science about it, there are still things that are unknown. Whether our predictions hold true or not remains to be seen in the future. But we think it’s highly likely, given what we know so far, Covid-19 will eventually become seasonal, like other coronaviruses,” Zaraket said in the study release.
But the real question is will that “eventually” ever become a reality?