Would 2009 H1N1 (Swine Flu) ring the alarm bell?

by AllAmericanBreakfast4 min read7th Apr 202013 comments

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CoronavirusWorld Modeling
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Introduction

In order to assist in anticipating and responding to the next pandemic, I created an "alarm bell" questionnaire to suggest whether or not one should behave as if the world is about to experience a stock market-crashing pandemic.

To evaluate whether it is correctly calibrated, my intention is to investigate whether the "alarm bell" would have rung during historical pandemics, and whether the stock market would have crashed before it rang, after it rang, or not at all. I have performed the first test, based on the 2009 H1N1/swine flu pandemic. The stock market did not crash, and in my analysis the alarm bell did not ring - but see the comments for caveats.

This is because 2009 H1N1 was much less deadly than COVID-19, and it also did not shut down the world economy. The "alarm bell" rings if 13 of the 16 below criteria are operative, but only 11 of the 16 criteria were ever met.

This is one point of evidence in favor of this alarm bell being correctly calibrated. I would also like to investigate this question for Ebola, MERS, SARS, HIV/AIDS, the 1968 Hong Kong flu, and (as far as it's relevant) the 1918 Spanish flu.

Stock Market Trends in 2009

The stock market was at a low point in 2009 around March 6th, but had begun a strong upward trend that would last the rest of the year by mid-March, when the first cases of swine flu were confirmed in Mexico. Although the New York Times reported stock market tremors related to swine flu on April 27th, 2009, looking at the data for the whole year, the daily fluctuations for the year look pretty much like a random walk (April 27th highlighted in red):

Factor 1: Transmissibility

  • Does the disease appear to spread from human to human?

Yes, as with all H1N1 flu.

  • Does the disease spread via indirect contact (coughing, sneezing)?

Yes, as with all H1N1 flu.

  • Is there any evidence that the disease is transmissible before or just after the start of symptoms?

Yes. According to a fact sheet released by the state of New Hampshire, "People with H1N1 flu virus infection should be considered potentially contagious one day before the onset of symptoms and as long as they are symptomatic, and possibly up to 7 days following the onset of illness."

  • Do any academic papers, especially in the Lancet or the New England Journal of Medicine, suggest the possibility of "risk of much wider spread," "exponential growth," or use similar phrases? Try searching "[DISEASE NAME] exponential growth" on Google Scholar.

A paper published on the 14th of May 2009 estimated that the "reproduction ratio was less than 2.2 – 3.1 in Mexico." For comparison, R0 for COVID-19 is estimated at 1.5-3.5. I count this as yes as of on or before the 14th of May 2009.

Factor 2: Harm

  • Is there evidence that the disease has a 3% or higher case-fatality rate among those 60 (or even younger), or 1%+ case-fatality among those 50 (or younger)?

This is one of the trickiest ones, because in early days when case rates are not known accurately, it's hard to predict. It's important to distinguish between confirmed case fatality rate and overall case fatality rate, and global vs. age-related CFR.

One recent scholarly global CFR estimate for COVID-19 is 0.51%. An estimate from the 7th of February put it at 0.18%-2.8%. So I will consider adding a global, non-age-based CFR threshold to the criteria.

This project is also not about estimating the true value of CFR; it's about normalizing a heuristic for deciding when to behave as if a new illness could be as serious as COVID-19.

So we have to ask what our threshold for evidence is. I can think of two possibilities.

  • Allow for extremely rough amateur division to meet this criterion. For example, in this April 27th 2009 New York Times piece, they wrote "Mexican health authorities have confirmed 149 deaths from that flu and are investigating the illnesses of 1,600 people." A reader who ignored the subsequent paragraph stating "... doctors have little information yet on the mortality rate, as there is no reliable data on the total number of people infected" might have divided 149 by 1600 to obtain a "case-fatality" rate of 9%, a wild overestimate of the true figure.
  • Alternatively, we could require a scholarly or government/major NGO case-fatality rate estimate. This scholarly editorial from September 2009 gave an Australian government estimate of 0.14% case-fatality. A November 2009 estimate was even lower, putting the rate at "0.026% (range 0.011-0.066%)." The earliest CFR I found was from June 19th, 2009, estimating a 0.4% CFR (range 0.3%-1.8%).

Given that it was predictable that there were many more undetected cases that lowered the true CFR, I'm going to disqualify the "rough division" from meeting the criteria and require a scholarly CFR estimates.

That 0.4% June scholarly global CFR estimates for swine flu were within the 0.18%-2.8% range of the Feb. 7th global CFR range for COVID-19. However, that Feb. 7th paper was pretty skeptical of these figures. I'd like to see if there was another COVID-19 estimate prior to Feb. 20th that presented an estimate with more confidence.

I provisionally count this as a no, but may change this later.

  • Can the disease last for two weeks in more serious cases?

From an NCBI paper: "The acute symptoms of uncomplicated infections persist for three to seven days, and the disease is mostly self-limited in healthy individuals, but malaise and cough can persist for up to 2 weeks in some patients. Patients with more severe disease may require hospitalization, and this may increase the time of infection to around 9 to 10 days." I count this as a "no," because it is only malaise and cough that persisted for 2 weeks, not the need for hospitalization.

  • Do around 5% of patients seem to require hospitalization?

By CDC data, upper bound of US hospitalizations divided by number of cases is less than 1% of cases requiring hospitalization. I count this as a "no."

  • Are there no vaccines and no treatments that have been proven effective?

Because flu was already known to be Tamiflu-resistant in 2008, by early January 2009 the CDC was already recommending Relenza (zanamivir) and other alternate treatments for H1N1. I count this as a "no."

Factor 3 - spread

  • Is the world death toll over 2,000?

The WHO's 61st pandemic update put the world death toll at "at least 2185" on the 23rd of August 2009.

  • Has the disease been detected in at least 10 industrialized countries collectively containing a total of at least 1 billion people, found in people with no clear link to the original source?

The first cases of what would later be confirmed as swine flu were diagnosed in Mexico in early March when 60% of the small town of La Gloria, in Veracruz, was sickened. It was confirmed in its 10th country, the Netherlands, in April 2009. It wasn't confirmed in a set of countries totaling a world population of at least 1 billion people until it was found in China on May 1st, 2009.

  • Is the disease present in major cities with strong international travel links?

The first community outbreaks in the US were confirmed on April 25th, 2009.

  • Has the disease spread in advance of a lockdown, or escaped it?

News of Mexico shutting down parts of its economy were reported in Reuters on April 29th, 2009. I'll count this as "lockdown."

Factor 4: Institutional response

  • Has a city-wide lockdown been attempted in a city of a population of at least 10 million, or have travel restrictions to or from major economies been implemented?

I don't find reports of major city lockdowns. The most significant travel restriction I can find was of Mexican travel to Japan. I personally don’t count 2009 Mexico as a “major economy” but that is a controversial and not pre-declared analysis decision. For future analyses I’ll use the 2009 Mexican fraction of world GDP as my cutoff for “not a major economy.” The WHO was recommending against travel restrictions early on. I count this as a no.

  • Has the WHO or a similar organization declared an "emergency of international concern" or "global emergency," or issued an even more severe warning?

The WHO declared swine flu a "public health emergency of international concern" on April 25th, 2009.

  • Have there been several front-page news stories about the disease?

There were multiple stories on page A1 in the New York Times by the last few days of April. There may have been earlier front-page swine flu news, but I'm not sure based on what's coming up on their digital search.

  • Are there reports or warnings of shortages of medical supplies from the most-affected regions?

Yes, there were mask shortages.

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