Will Spring Slow The Spread of COVID-19?

One of the most well-known aspects of influenza, more commonly known as the ‘flu,’ is that it occurs in yearly, seasonal outbreaks, with infections increasing as much as ten times from their summer minimums during the dark days of winter. This is also true with the common cold, which is not a specific virus like the influenza virus but is an umbrella term for a mild upper-respiratory infection caused by over 200 virus types. The fact that these viruses favor winter has been attributed to people spending more time indoors and thus facilitating person-to-person transmission of the virus, and the colder, drier weather may also be a more favorable environment for the viruses themselves. The cold/dry weather and reduced UV radiation allows viruses to survive longer on exposed surfaces, and these same cold and dry conditions dehydrate mucous membranes and make them more susceptible to infection. Finally, kids are in school during the winter months, and if there’s anybody who knows how to spread germs around, it’s those little rascals!

Coronaviruses are relatively common and are responsible for approximately 15% of all cases of the cold. But the novel coronavirus that has resulted in thousands of deaths, hundreds of millions quarantined, and a record selloff in global equities has proven to be a particularly virulent strain. This novel coronavirus, known officially as “Coronavirus disease 2019” (COVID-2019), has approximately a 1-2% mortality rate, approximately 5 times less than the 2003 SARS outbreak in China, another coronavirus, but 10-20 times higher than the mortality rate for the seasonal flu.

In response to the high mortality rate, fast spread, and lack of any vaccine against COVID-2019, the WHO designated the novel coronavirus outbreak as a global pandemic last Wednesday 3/11. Countries all across the world have taken extreme measures to contain the virus, and while new cases have dropped precipitously locations like China and South Korea and life is beginning to return to normal, cases are still increasing exponentially in many European countries, and I fear the US is on the brink of a major surge in cases. If you are looking for the most accurate and up-to-date information regarding the coronavirus, the World Health Organization’s daily “Situation Reports” are a fantastic resource.

When reading about the coronavirus, I stumbled across a Forbes article written by Dr. Marshall Shephard, a well-known atmospheric sciences professor at the University of Georgia. The article, titled “Will Spring Temperatures Stop Coronavirus?”, came to an admittedly unsatisfactory conclusion; that we simply don’t know at this time. Marshall cited the CDC’s COVID-2019 FAQ page in making his assertion, as the CDC states that it is “It is not yet known whether weather and temperature impact the spread of COVID-19.”

To be clear, I’m taking the CDC’s position here. This is a novel virus with unique characteristics, and it is impossible to know if warmer weather would ameliorate its spread at this time. However, I thought it would still be worthwhile to study the seasonality of some past pandemics and how they differ from the ebb and flow of the endemic viruses that traverse the hemispheres through the seasons, and if we could at least draw some conclusions about their spread rate relative to the seasons. As an obligatory disclaimer, I do not have any background in epidemiology, and these are just my musings on my personal blog. You should use official sources like the World Health Organization or Center for Disease Control to get the most accurate and up-to-date information.

The Greatest Pandemic In Modern History – The Spanish Flu of 1918

The bubonic plague, or “Black Death,” that ravaged Europe during the mid 14th century was the most devastating pandemic in recorded history, wiping out approximately 1/3rd of the entire continent’s population. But the bubonic plague was caused by a bacteria – yersinia pestis – in infected fleas living aboard rats, not a virus. With incomparably better sanitation than the 14th century, the plague is now extraordinarily rare in the developed world, with the US averaging less than 10 cases a year over the past decade. Moreover, many cases that do occur can quickly be treated with strong antibiotics, though they must be administered extremely rapidly after symptoms arise. Unfortunately, several thousand cases still occur in the developing world each year, but it is still a far rarer disease than some other bacterial diseases, such as cholera or tuberculosis.

The greatest viral pandemic in modern history was the Spanish Flu of 1918. According to the CDC, approximately 1/3 of the world’s 1.8-1.9 billion people contacted the virus, and at least 50 million people died from it. To be sure, the Spanish Flu was an extraordinarily virulent and contagious version of the influenza virus, but the pandemic was substantially amplified by World War I, as the combination of close quarters, unsanitary conditions, and mobile troops spreading the virus worldwide created a perfect storm for a global pandemic to ensue.

There were three “waves” of the Spanish Flu – the initial outbreak in spring/summer 1918, the second, deadliest outbreak during autumn 1918, and a third outbreak in winter/spring 1919 that was somewhere between the first and second outbreaks in severity. We do not have sufficient data to definitively trace the origins of the Spanish Flu, but there are three proposed centers where the flu may have arisen – France and/or China in late 1917, and Fort Riley, Kansas in March 1918. Below is a timeline I created highlighting some notable events in the pandemic.

The graph below shows the mortality rate (deaths per thousand per week) of New York, London, Paris, and Berlin during 1918 and 1919. Notice how fast the cases rose in October – this illustrates the exponential growth of pandemics when relatively few precautionary measures are taken. Cases fell dramatically in November due to the virus killing off its hosts in October and mutating to a less severe form in order to survive.

As you can see, the Spanish Flu did not follow the typical “seasonal flu” profile; the second, deadliest wave began in August, peaked in late October/early November, and was over by December. As mentioned earlier, it is true that influenza viruses last a much shorter time on warm, humid surfaces and are easily killed by UV radiation, and that the behavioral shifts in winter (such as spending more time indoors) are more efficient at spreading contagious diseases. However, the Spanish Flu was far more contagious than the seasonal flu since most people had little-to-no-immunity to the virus and was able to easily overcome these seasonal barriers.

The 1918 Spanish Flu was so virulent that young, healthy adults could die less than 12 hours after showing their first symptoms. Most viruses of this virulence do not grow into a pandemic, as they kill their hosts before their hosts can spread the virus to others. The Spanish Flu thrived in large part because it was sustained in the trenches; the trenches were a perfect environment for the virus to spread among pre-existing soldiers, and new, uninfected soldiers were constantly being deployed to replace those that had died, either from battle or from the virus. Soldiers then interacted with the local population, spreading the virus and allowing it to subsequently ravage other communities.

The 2009 Swine Flu

With the exception of AIDS, which has been a pandemic since 1981 – the last pandemic was the Swine Flu in 2009. The Swine Flu had the same influenza subtype – H1N1 – as the Spanish Flu, and it infected between 700 – 1400 million people worldwide. However, with ‘only’ 150,000 – 575,000 fatalities, the Swine Flu had a fatality rate of <0.1%, indicating that the Swine Flu was less virulent than the Spanish Flu and showing how far modern medicine has come in treating flu pandemics.

Like the Spanish Flu, the Swine Flu first arose in the spring, and then a second, stronger wave arrived in the autumn, with cases peaking in mid-October.

Recent Coronavirus epidemics: SARS and MERS

COVID-19 is the first coronavirus pandemic, but many of us remember two other coronavirus epidemics – SARS from November 2002 to June 2003, and MERS in 2012 and 2015. SARS has been completely contained, while MERS continues to circulate at low levels. Because SARS lasted only one season, we can’t really infer any seasonality from it, and MERS does not have a predictable seasonal pattern.

When we take a holistic look at 20th/21st century influenza/coronavirus pandemics/epidemics, we do not find a clear, seasonal factor like we do with endemic influenza and the common cold. I can only infer that this is because these influenza/coronavirus strains are ‘novel’ viruses with which there is little or no pre-existing immunity, and they can be easily spread throughout the population regardless of the season. To reiterate the CDC: we do not know enough about COVID-19 yet to know if it has a seasonal cycle. But if past upper-respiratory (namely, influenza and coronavirus) pandemics are any clue, seasonality might not play that big of a factor.

One thing is for sure: how countries are responding to the virus has a much, much greater impact on its spread than the season. Just compare the graphs of confirmed cases in China vs the U.S. After initial exponential growth, the Chinese government issued draconian but highly successful lockdowns on major cities and got testing kits to millions of people, and the virus is now effectively contained with now only dozens of new cases per day. But even with months of lead time, the US was woefully unprepared, and cases continue to grow at an exponential rate. Australia is also currently seeing an exponential increase in cases, despite the fact that it is late summer there.

This virus has exposed how healthcare is not a service, or even a right; it is a national security issue that holds the fabric of our economy and society together. The US may have been able to sidestep a severe recession if we had the resources to provide free, public COVID-19 tests to all citizens, as South Korea has done. Unfortunately, we were not prepared, and we now must practice isolation and social distancing instead, which is far more damaging to our economy and society. The S&P 500 saw its 2nd-largest percentage decline in history on Monday in response to the Fed announcing on Sunday that it would take extraordinary measures to stimulate the economy, and I worry about many local businesses going bankrupt due to the prolonged loss of business.

And finally, part of me worries that even when the greatest danger from the coronavirus has passed, our experiment with social distancing and self-isolation will make us irrationally risk-averse. This is personal for me, as I have epilepsy and risk calculation is a part of my everyday routine.  People need a quantitative framework to assess risk, and I just hope that our experience with avoiding infection at all costs (and for good reason) won’t scare us from taking chances in the future.

I’ll mainly be at home for the foreseeable future, so I’ll be frequently posting on my blog! Much material will of course be weather-related but I may also have more coronavirus musings, seeing as it is the story of our time.

Thanks for reading and stay safe!
Charlie