As the novel coronavirus began spreading around the world this year, one common refrain from skeptics of the emergency measures being put in place to stop the outbreak was that it was just like the flu -- dangerous to sensitive groups but routine and not something to get into lockdown over.
We now know that assessment is wrong. At its lowest estimated fatality rate based on current data, Covid-19, the disease caused by the coronavirus, is thought to kill some 1-2% of known patients, compared to around 0.1% for winter influenza. The coronavirus also appears to be about as infectious as the flu, and potentially more so, especially as there are no specific treatment, cure or seasonal vaccine.
There is one area in which experts hope the virus will still behave like influenza, however, by tapering off in spring.
"This is a respiratory virus and they always give us trouble during cold weather, for obvious reasons," Nelson Michael, a leading US military medical researcher, said of the novel coronavirus last week. "We're all inside, the windows are closed, etcetera, so we typically call that the influenza or the flu season."
Influenza thrives in cold and dry conditions, which is why winter is flu season for much of the northern hemisphere. Behavioral differences in winter can also have an effect. Michael predicted the coronavirus may behave like the flu and give us "less trouble as the weather warms up," but, he cautioned, it could come back when the weather gets cold again.
The hope is that, along with radical action by governments and the public to decrease the number of new cases, reduced spread during warmer weather would give health systems space to cope with the initial influx of coronavirus patients, and buy time for a potential vaccine to be developed.
"This is why it's really important to understand that a lot of what we're doing now is getting ourselves ready for what we're calling the second wave of this," Michael warned.
But what if the virus does not behave like influenza? Could we be dealing with infection rates that remain high throughout the year? More than 100 cases have been confirmed in Singapore, where it's hot and muggy pretty much year round. Australia, Brazil and Argentina, all currently in the middle of summer, have also reported dozens of cases.
Unknown unknowns
There is evidence to suggest the coronavirus does particularly well in certain climates.
Some of the worst hit areas around the world -- from Wuhan, where the virus was first detected, to Iran, Italy and South Korea -- are on more or less the same latitude, with similar temperatures and relative humidity. Researchers at the University of Maryland (UM) have even used this data to attempt to map out other parts of the world that could be at risk of imminent outbreaks.
Though the research remains preliminary, data from the UM study suggests that certain climatic conditions, while not determining whether the virus can survive, may help accelerate its spread.
"In addition to having similar average temperature, humidity, and latitude profiles, (locations along latitude 30-50°N) also exhibit a commonality in that the timing of the outbreak coincides with a nadir in the yearly temperature cycle, and thus with relatively stable temperatures over a more than a one month period of time," the authors wrote.
Brittany Kmush, a public health expert at New York's Syracuse University, who was not involved in the UM study, said that "influenza and other coronaviruses that infect humans tend to follow a seasonality, with cases peaking in the winter months in the northern hemisphere. However, we don't know if this virus will follow a similar seasonality pattern."
David Cennimo, who studies infectious diseases at Rutgers New Jersey Medical School, said that many experts "hope -- and I think the correct word is hope -- that the summer will push down the case numbers," though he added that "the data from tropical countries may rain on this hope somewhat."
However, both Cennimo and Kmush cautioned against drawing too many conclusions from the geographical data, pointing to the many unknowns that remain about the virus itself and its spread in recent months.
"The question is, are (tropical cases) travel associated, connected to a known case, or cases of unknown origin," Kmush said. "If there is seasonality, we would expect connected cases and cases of unknown origin to decrease as the temperature becomes warmer. I think it is really too soon to tell if we are going to see a seasonal pattern with Covid-19 or not."
Debra Chew, an assistant professor of medicine at Rutgers, agreed that the lack of understanding of the virus and how it behaves makes predicting anything like seasonality largely impossible at this point.
"The dynamics for control of the epidemic may rely on factors that influence transmission of the virus such as infectiousness and spread or the virus by persons having mild or no symptoms, or by behaviors to reduce the spread of the virus," she said. "We are not dealing with a virus like influenza that behaves predictably every year."
Seasonal scare?
Even as cases of the coronavirus have spiked alarmingly in many countries this week, there has also been a glimmer of good news. Outbreaks in both China and South Korea, previously two of the worst hit countries, appear to be stabilizing, with fewer new cases week on week. That is thanks to prolonged intervention by health authorities, including a combination of lockdowns, travel restrictions and encouraging people to work from home and exercise social distancing, as well as helping to educate the public on the need for strict sanitization protocols.
It remains to be seen though, as areas that were at the forefront of the outbreak begin relaxing restrictions, whether cases will climb again, or if the virus is truly under control. As other parts of the world only just ramp up actions to deal with it, many hope they will get a boost from warming weather. However, even if they do, this may not mean the virus is done with us.
"There really still is so much unknown about this virus," Kmush said. "If case numbers decrease over the summer, it is a good idea to prepare for a resurgence during the colder months."
