Evidence and Epicurves

Donald Henderson was an American Epidemiologist who led the World Health Organisation campaign that eradicated Smallpox.  This was a highly infectious disease with airborne transmission (meaning fine particles that remain suspended in the air for significant periods of time after they’ve been coughed out) as well as other transmission routes.  A comprehensive overview of the clinical presentation of Smallpox is available at Medscape, here.

According to Wikipedia, when the Smallpox eradication campaign began in 1966 it caused more than 10 million cases and 2 million deaths every year.  Within ten years the disease had been eradicated worldwide, in large part thanks to a targeted and coordinated vaccination campaign (including post-exposure vaccination).  An Analysis of the United States and United Kingdom Smallpox Epidemics (1901-1905) – The Special Relationship That Tested Public Health Strategies for Disease Control published in January 2020 is an excellent historical account of the way Smallpox spread between Boston USA and Liverpool England in the era of trans-Atlantic steamship travel. It discusses the public health challenges and principles employed which were used 70 years later by Henderson’s Smallpox Eradication team.  Just as his predecessors in Boston and Liverpool became renowned public health leaders, Henderson’s campaign leadership placed him as one of the world’s most recognised Epidemiologists.  He died in 2016.

In 2006 Henderson co-authored a review titled Disease Mitigation Measures in the Control of Pandemic Influenza for the Center for Biosecurity at the University of Pittsburgh.  The authors describe the epidemiological characteristics of Influenza as having a rapid transmission rate, being infectious without symptoms, and being difficult to distinguish clinically from other respiratory illnesses, all of which can also be said about SARS-CoV-2.

The geographical, seasonal and temporal limitations of previous Influenza pandemics are described.  This includes the 1918 Spanish Flu, when transmission in any community lasted an average of about eight weeks.  This is in keeping with the timeline for Covid-19 when you look at the epidemiological curves for different locations.

The purpose of the Henderson review was to consider whether specific mitigation measures are “epidemiologically sound, logistically feasible and politically viable… and to consider possible secondary social and economic impacts“.  The review expressed a need to consider potentially adverse consequences when mitigation measures are implemented, including social and economic harm and impact on essential service capacity.  They identified that current pandemic plans offered options for mitigation measures but did not provide implementation criteria or operational detail.  These would seem like serious omissions when you look at the haphazard, media- and politically-driven decisions being made in many places today.

The limitations of computer modeling to predict pandemic patterns are discussed in the review.  Models can’t predict human behaviour or the knock-on effects of mitigation strategies, and are therefore recommended as a useful aid in speculating about measures, but should not decide policy.  A computer model created at Imperial College in London, since acknowledged as not meeting current standards of scientific rigour and not peer-reviewed, drove global lockdown policies from March 2020.  The main author of this model is Neil Ferguson, an Epidemiologist whose modeling projections have previously been vast over-estimations, as shown by the Montreal Economic Institute: The Flawed Covid-19 Model That Locked Down Canada.

Computer Modeling Predictions vs Reality

The Henderson review examines specific mitigation strategies in some detail, with reference to the evidence of effectiveness, whether implementation is feasible, and the possible adverse consequences of each.  The measures evaluated include:

  • Vaccination
  • Hospital isolation of the sick
  • Home isolation of the sick
  • Antiviral medications
  • Handwashing and respiratory etiquette
  • Quarantine of possibly infected people
  • Travel restrictions
  • Prohibition of social gatherings
  • School closures
  • Physical distancing
  • Use of masks and personal protective equipment (PPE)

It is worth understanding each of these measures rather than merely listening to and trusting our politicians and the media.  An informed society are less likely to be misled by fear and anxiety.  These two links, both written before the political and media frenzy of 2020, are a good start:

Some Interesting Epicurves

In 2019 face masks were valued at $122 million of the US stock market compared to Q1 of 2020 when they had risen exponentially to $74.9 billion according to this Grand View Research link.  It was at the beginning of Q2, 2020 when mask recommendations suddenly changed from “they may do more harm than good”, to “we recommend their use”.  The science behind how and when masks work has not changed and did not lead this recommendation change, so after decades of working with and teaching about masks, I remain mystified despite searching for sensible explanations.  I don’t want to be anchored to outdated evidence, but robust and convincing new evidence has not been forthcoming.  The timing may be coincidental but I think it’s valid to ask, has poor planning allowed stock market forces to influence public health policy?

France’s Epicurve: Why Masks Now?


Argentina’s Covid-19 – Mitigation Measures Relationship


Epicurve NYS vs Sweden
New York State Compared to Sweden

Sweden’s Covid-19 response is often quoted as an example of how not to implement public health measures.  This has consistently staggered me as their State Epidemiologist Anders Tegnell seems to have been a calm, humble presence who has followed the evidence, been honest about mistakes (namely the time it took them to put proper measures in place to protect aged care facilities) and held firm in the face of global anxiety and disapproval.  He seems to confidently understand the principles of public health and have the courage to implement them despite criticism.  One of the criticisms is that despite not locking down, their economy has still been damaged.  However, that has been a direct result of their trading partners locking down.  One of Sweden’s reasons for not implementing tough lockdowns was the risk of disease re-emergence when lockdowns were eased.  Australia seems to be a case in point?

From Tomer Burg, Meteorology PhD Student and Data Artist, at http://arctic.som.ou.edu/tburg/products/covid19/

Dr David Nabarro, WHO Special Envoy on Covid-19, has this to say about lockdowns:

Locking down your economy is not the way you get ahead of Covid.  It basically stops the virus in its tracks, and it gives you a breathing space.  But the way you get ahead of Covid is by interrupting transmission, busting the clusters and suppressing the outbreaks.  And it’s doable.  It does cause some inconvenience; you do have to isolate people with the disease, you do have to isolate their contacts.  It may mean some local movement restrictions.  But absolutely not locking down a whole economy unless things are really, really bad.  And I’d like everybody to know this.  You can get ahead of this virus without having to do lockdowns.  You can get ahead of this virus and still keep the economy and society going, but there will be some changes necessary, including how we behave and including how our health services work“.

He falls short of mentioning the harm done.  The lockdown catastrophe has swept in rapidly on the world’s most vulnerable, with millions facing famine and devastation.  Nabarro has called for world leaders to collaborate on a coordinated global response.

The 2006 review by Henderson and colleagues ends with these words of wisdom:
An overriding principle.  Experience has shown that communities faced with epidemics or other adverse events respond best and with the least anxiety when the normal social functioning of the community is least disrupted. Strong political and public health leadership to provide reassurance and to ensure that needed medical care services are provided are critical elements. If either is seen to be less than optimal, a manageable epidemic could move toward catastrophe.

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