(A disclaimer: this post will be more speculative than my usual posts, however I intend to back up my speculation with data where available.)
After months of outbreaks, COVID-19 cases are now declining in most U.S. states. This is great news in the short-term, but many of us are wondering whether and how soon COVID-19 outbreaks will return.
There are a lot of good reasons to suspect that COVID-19 may return this winter. First, while flu and other respiratory viruses circulate all year, they tend to peak in the winter. In fact, a study published on July 1, 2020 in the Journal of Infectious Diseases found that routine (non-COVID) human coronaviruses peaked very predictably between December and April over 8 years of monitoring.
Second, the H1N1 influenza pandemic had an initial peak in April and May 2009, followed by a second larger peak in October through December that year. While the COVID-19 pandemic is caused by a different virus and has many different characteristics from the H1N1 pandemic, the similar seasonal patterns of routine human coronavirus and seasonal influenza suggest that COVID-19 might return on a similar time frame to H1N1’s second peak.
Third, many Southern Hemisphere countries had initially-low rates of COVID-19 earlier this year (in their summer) but subsequently peaked in July and August (their winter), consistent with a pattern of winter outbreaks.
Finally, a study published in Transboundary and Emerging Diseases in May 2020 and a follow-up published by the same authors in August 2020 found that every 1% decrease in relative humidity is associated with a 6-8% increase in cases of COVID-19. Continuing the parallel with influenza, previous studies have found that influenza viruses spread through simulated coughs were less infectious in environments with higher humidity and that seasonal changes in humidity in the United States predict changes in influenza spread.
In conclusion, I think it is very likely that COVID-19 will return in the United States, possibly as soon as this October. I would very much like to be wrong in this matter. However, in my opinion the best thing that we can do is to prepare for this possibility.
None of us know if or when we will be in a car accident, and we hope we never will be, but we buckle our seat belts and our children’s seat belts in case of an accident. In the same way, it’s critical that we continue to wear face masks, social distance, wash hands regularly and teach our children to do the same, even if there isn’t much COVID-19 activity in our local areas. There’s good reason to suspect COVID-19 will return this fall and/or winter, so stay vigilant. Scientists around the world are working hard to develop and test potential COVID-19 vaccines and better treatments, but until those are available, we need to continue to do our part.
One last thought: I’m cautiously optimistic that if we continue following the basic simple steps to prevent COVID-19, then the next wave may not be as severe as the first wave. We’re more familiar with the symptoms of COVID-19, early warning signs of an outbreak, the steps that help to control it, and public health departments are doing extensive contact tracing initiatives that they didn’t have the resources to do earlier this year. If we remain vigilant and maintain our public health systems, then we ought to be able to detect the beginnings of the next COVID-19 outbreak earlier than we did last spring, and respond more quickly to control it. But if we become complacent and try to return to “normal” too soon, then we could have very large outbreaks, as we did this summer when several states reopened before they were ready.
Stay safe, stay healthy, and stay vigilant,
š· Dr. B