Monty Python and the quest for herd immunity

Jun 16, 2020

Like the Holy Grail, ‘herd immunity’ often seems to involve miraculous powers, and its advocacy to contain the Covid-19 pandemic has far more to do with faith than evidence.

King Arthur and the Knights of the Round Table has been a boys’ own story enjoyed for generations.  The knights created an oasis of chivalry, bravery and service in Camelot, and were united in their quest for the Holy Grail.  The grail, sometimes said to be the cup Christ drank from at the last supper, has miraculous powers, including for example bestowing eternal youth on its holder.  More recently Monty Python transformed this book of derring-do into a riotous comedy.

Herd immunity refers to a situation where the proportion of immune individuals in a population is sufficiently high to produce a decline in the incidence of infection.  Individuals have become immune either through vaccination or through the presence of antibodies from past exposure to the virus.  Once a certain proportion of the population has become immune this indirectly helps those who might still be susceptible because there is a reduced risk of contact.

Herd immunity is a grand phrase, sometimes justified by the results such as the elimination of that centuries-old scourge of humankind smallpox.  A more prosaic phrase such as reduced risk is usually more appropriate.  For example in contagious diseases such as measles and whooping cough, mass vaccination has radically reduced the number of cases, but not yet been sufficient to eliminate them.

Historically, herd immunity was important in contacts between European colonists and indigenous populations, who were suddenly exposed to diseases with which they had had no previous contact, and the spread of disease was often more deadly than the force of arms.

All major modern cases of herd immunity are due to extensive vaccination programs.  The proportion of immune individuals needed to produce a large fall in the incidence of the disease varies, according to some it has to be over 90 per cent immune to keep measles at bay, but for others, it may be lower at 60 or 70 per cent.

The amazing thing in the current pandemic is that some people are advocating herd immunity in the absence of a vaccine.  Former NSW Liberal Minister Pru Goward was quite explicit: she thought that Australia could not remain in hibernation for months on end, and ‘accepting as we now do that a vaccine might never be possible’ wants instead of staged herd immunity.

Some version of vaccine-free herd immunity – despite later official denials – seems to have played a role in the British Government’s thinking at a crucial time, delaying their eventual lockdown response.  A recent documentary quotes Italy’s Health Minister saying that Boris Johnson told Italy’s prime minister the UK had been aiming for coronavirus herd immunity.  Sir Patrick Vallance, the chief scientific adviser to the UK government, said publicly on March 13 that he believed the UK would be able to achieve herd immunity.  Later in the month, the British Government took much more drastic steps, but too late to put the pandemic back in its box.

Sweden also pursued a strategy of what it hoped would be a managed spread.  However, by May 20, it had had 3743 deaths from the coronavirus and a much higher fatality rate than its Nordic neighbours.  In Sweden 371 people per million had died, far higher than Denmark’s 95, Finland’s 54 and Norway’s 43.  The progress this heavy toll made toward herd immunity was slight – by the end of April just seven per cent of Stockholm’s population had Covid-19 antibodies, a far lower figure than officials had anticipated, and there are now some statements of official remorse.

The Economists who say Ni – Always look on the bright side of death

Elsewhere advocates of herd immunity do not seem to have shaped actual policies, but they have often been strong voices from the sidelines, especially those bemoaning the economic damage wrought by lockdown responses.

Prominent academic economist Gigi Foster is one such: ‘Has anyone thought about how would you get a measure of the traded lives when we lock an economy down?  What are we sacrificing in terms of lives?  If you do that kind of calculus you realise very quickly that even with a very, very extreme epidemic in Australia, we are still potentially better off not having an economic lockdown in the first place because of the incredible effects that you see not just in a short-run way but in many years to come.’

She seems to be saying that a lockdown would never be justified, that it always would produce more suffering than an extreme epidemic.  At the least, this is an article of faith rather than a judgement relying on any evidence.

This reliance on dogma rather than evidence often characterizes the contributions of economists.  For example, the Wall St Journal’s Holman W Jenkins asserted ‘Sweden’s neighbours are not avoiding the same deaths with their stronger mandates, they are delaying them, to the detriment of other values.’  He did not feel compelled to offer any evidence, and so far nothing to justify this certainty has been forthcoming.

These economists stress the costs of a lockdown, but often proceed as if the economy would otherwise still hum along, with good investment opportunities in funeral parlours.  In contrast, a group of over 100 Australian economists wrote an open letter decrying the morally objectionable indifference to the loss of life, but also making the key argument ‘We cannot have a functioning economy unless we first comprehensively address the public health crisis.’

‘What has the government ever done for us?’

Australia has so far had great success in containing the pandemic, with a total of 102 deaths and a fatality rate of four per million population.  If Australia’s fatality rate had been the same as Britain’s, for example, there would have been over 13,000 deaths by now.

Perversely Australia’s very success has made it possible for a small cabal of critics to argue that the measures were unnecessary, a little like saying that since we have safely landed it shows we never needed a parachute.  For example ‘Tony Abbott’s former economist’, Andrew Stone, said the shutdown was wrong as the threat posed by the coronavirus was not as large as first feared.

The Australian’s economics editor Adam Creighton has been a faithful conduit for such views.  He described the letter from the economists cited above as bizarre, and said there was no evidence government measures had worked.  Instead, he posits that Australia’s relative success may be due to ‘Australia’s weather, relative population density or island geography.’

Creighton also quotes Nobel Prize-winning biologist Michael Levitt, who said the response was ‘massively’ damaging the economy and decried the ‘panic’ stemming from ‘incorrect numbers’.  He said the damage from the lockdowns ‘will exceed any saving of lives by a huge factor’.  Professor Levitt said ‘herd immunity’ was the right policy and Britain ‘was on exactly the right track before they were fed wrong numbers’

Again the most notable feature of this biologist’s socio-economic assertions is the lack of any supporting evidence.

Merlin Finds the Magic Trade-Off

For the last few months, two different disasters have dominated the news.  The first is about the spread of the pandemic; the second about the collapsing economy.

All policies involve trade-offs, but the difficulties in the current situation are acute, with very high stakes – deaths and recession – and two very different goals seemingly competing to be the priority.  Perhaps most importantly, the decision-making is occurring amid great uncertainty, without clear knowledge of what policy-makers can control and what they can’t, where the risk of unintended consequences is particularly high.

From almost the beginning of the pandemic, people have been looking forward to it being over.  Scott Morrison fantasised that the economy would then ‘snap back’.

Australia currently has very low rates of domestic transmission of the virus, and properly, attention has turned to when and how to re-open social and economic life.  But that does not mean the pandemic is finished.

Indeed globally there are still over 100,000 new cases every day, so at the very least international movements will not be snapping back.  Within Australia, there are likely to be clusters of outbreaks, so that disruptions at local levels will keep on happening.  The months ahead, balancing competing priorities, are likely to be messy.

It will be a future with tracking, testing, quarantine and social distance, but it will be aimed at containing the virus, not allowing it to spread in search of some holy grail of herd immunity.

What would herd immunity without a vaccine involve?  Let’s assume sixty per cent of the population having the anti-bodies will be sufficient, and let’s assume the fatality rate for those affected will be 0.5%.  Then herd immunity in a population the size of the US would require around 200 million people to be infected, which would mean around one million deaths.  In Australia 15 million would need to be infected, leading to about 75,000 deaths.

It must be remembered that we have known of this virus for less than half a year, and there is still so much unknown.  These assumptions may be too optimistic.  The proportion needing to have the antibodies may be considerably higher.  The fatality rate is the best guess at the moment.  We do not know how long immunity will last or short of fatalities whether there will be other lasting effects on those contracting the virus.

But we know enough to know that the prospect of herd immunity without mass vaccination is a cruel hoax, one which should have no part in any debate grounded in evidence rather than dogma.

It is a dead parrot.

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