While many parts of the world appear to be near the peak of their current Covid-19 outbreaks, health officials in the US are warning that a second wave could strike in winter – and it holds the potential to be even more devastating than the first.  

Robert Redfield, the director of the US Centers for Disease Control and Prevention (CDC), told the Washington Post that the US could face a second wave of Covid-19 later in the year that will be even more catastrophic than the current wave because it will clash with the start of the seasonal flu season.

“There’s a possibility that the assault of the virus on our nation next winter will actually be even more difficult than the one we just went through,” Redfield said in an interview with the Post on Tuesday. “And when I’ve said this to others, they kind of put their head back, they don’t understand what I mean.”

“We’re going to have the flu epidemic and the coronavirus epidemic at the same time,” he said.

Each year, typically in the fall and winter, the annual influenza season puts a mammoth strain on healthcare systems. The 2018-2019 influenza season in the US saw around 490,600 hospitalizations and 34,200 deaths from the flu. As we’ve seen recently with the ongoing Covid-19 outbreak, this too puts a huge strain on hospital beds, medical equipment, and healthcare professionals, even in the best-prepared parts of the world.

Fortunately, the worst of the influenza season was over by the time the wave of Covid-19 infections took hold in most parts of the world. If this wasn’t the case, however, it could have spelled serious trouble. Redfield notes that if the Covid-19 pandemic peaked during the winter months at the same time as the flu season, “it could have been really, really, really, really difficult in terms of health capacity.”

While there’s no telling how severe the next burst of infections could be, nor when it might peak, scientists have been worrying about the idea of a “second wave” for some time. 

“The most plausible scenario to me is for the COVID-19 pandemic to wane in the late spring (in the Northern Hemisphere), and come back as a second wave in the winter, which I expect could be even worse than what we’re facing now," Francois Balloux, a professor of Computational Systems Biology and Director of UCL Genetics Institute at University College London, commented in March 2020. “Something similar happened in 1918/1919."

Indeed, the 1918 Spanish flu pandemic is a powerful reminder to be aware of the second wave. In total, the influenza outbreak is thought to have killed over 50 million people, with some estimates going as high as 100 million. The first wave resembled a fairly typical flu epidemic. However, once the second wave came towards the end of the summer, the fatality rate skyrocketed.

Comparisons of Covid-19 with other disease outbreaks should be treated with caution, but it would also be foolish to ignore warnings from history.