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Pandemic Feedback

Dynamic living processes get into feedback loops. The most common is a negative feedback loop, whereby processes self-regulate; when something happens then something else happens, in response, to offset the initial event. If it gets cold, we put on another layer of clothing. If a consumer good becomes scarce, its price will go up, and we buy less of it. As 'loops', these are incremental 'trial and error' processes. We may still need to adjust our clothing further. And the price of something falls in stages, following a consumer feedback response as noted.

Sometimes however we get into destabilising 'positive feedback loops'; these may involve 'arms races', 'races to the bottom', or 'tipping points'. We understand that economic 'negative externalities' generate adverse environmental consequences which may in turn lead to unsustainable economic behaviours arising from desperation; anthropomorphic climate change may be reaching an irreversible tipping point.

The Great Depression was 'great' because policy responses – for a number of years – became a part of the problem rather than part of the solution; most particularly, retrenchment of government spending and financial supports. Eventually new insights brought about new responses, and the global Depression stabilised to some extent. While negative (stabilising) feedback eventually prevailed, that was not soon enough to prevent World War Two (WW2); and indeed WW2 may itself be classed as feedback.

Covid19 Immunity Feedbacks

We know that evolution involves 'arms races' between species and their predators. While the main relation between species and their resident microbes is one of equilibrium – negative feedback – novel microbes can become dangerous micropredators. Indeed viruses, as we mostly understand them, are viral micropredators. Coronaviruses are micropredators (aka 'pathogens'). People (as a host species) may be infected by coronaviruses new to humans, and then find ways to fight them off. The viruses – which, by their nature, can evolve rapidly – fight back, and people in turn fight back (for example with vaccines). We know that these particular arms races generally do not go on forever, because we coexist with a number of community coronaviruses for which we have an 'endemic' equilibrium relationship; viruses which were new, once.

For people – and other species subject to viral predation – there are three endgames. First is a return to normality achieved through a long-term elimination of the virus. (We can say that the 2003 coronavirus SARS-COV1 has been eliminated, though not eradicated. If it returns, it will be, in effect, a new virus; that's because it was eliminated quickly; and because it has been eliminated for a long time, at least by the standards that apply to coronaviruses.) Second, and most extreme, is the elimination of a host species; the virus may itself avoid co-elimination by switching to one or more other host species.

Third is the development of an equilibrium between host and virus; the virus ceases to be novel, and the host species gains 'herd immunity' to that virus. There is a problem though, for host species, because immunity tends to wane; for different types of pathogen the rate of deimmunisation varies. Coronaviruses, as a class, would appear to be one microbe type for which deimmunisation is relatively rapid. (For a number of microbes associated with severe disease immunity is not only acquired, it may also be inherited. The means through which inherited immunity takes place is little known, but almost certainly through non-predatory microbes within the microbiome. The most important historical example is the very uneven 'Columbian exchange' through which Native Americans suffered a mass die-off from diseases from which Europeans, Asians and Africans had attained inherited immunity.)

Biohistory can be understood as an arms race that takes the form of a sequence of individual 'games' (where our struggle with Covid19 is such a game). For species such as humans to survive (or at least to survive in sophisticated urban civilisations), this is an arms race into perpetuity. As new micropredators evolve, humans need to acquire – in historical time – more immunity to more pathogen species. By and large, humanity has done this in the past without massive public health interventions; although there is a long and honourable history of intervention to diseases, with the development of vaccinations – starting with cowpox to beat smallpox – playing a particularly important role. (The word 'vaccine' derives from a Latin word 'vacca' for 'cow'; vache in French.)

So that's the background. Vaccines as a public health response may lead to elimination or to equilibrium. Some vaccines require boosters – reimmunisations to maintain an uneasy equilibrium – the most familiar of these being the relatively recent influenza vaccine, for which vulnerable people need annual revaccinations.

The question posed here, however, is whether – and under what circumstances – public health policy responses may lead to adverse positive feedback, such as a 'race to the bottom'. (We have noted that vaccines contribute to the antiviral arms race, which, while a necessary and beneficial form of positive feedback in large domesticated populations, requires micropredators to themselves become fitter in an evolutionary sense. We may also note that our use of antibiotics has been central to an antibacterial arms race; a race that may be reaching its tipping point.)

The race that I am particularly concerned about is that between immunisation and deimmunisation. Immunisation takes place both naturally – the traditional way – and artificially (through vaccinations). The availability of vaccination technology does not mean that natural immunisation becomes unimportant. (It would appear that high levels of immunity to Covid19 at present in the European Union is due to a mix of both natural and artificial immunisation.)

To assess the likely outcome of this race, in relation to the present pandemic, we need much better knowledge of both natural immunisation (including co-immunisation) and deimmunisation. While these processes may be unaddressed (as 'unknown unknowns') by public health policymakers, the mere fact that I (and others before me) are raising these issues graduates them to 'known unknowns'. Any question that is posed, but unanswered, is a known unknown. (Further, 'knowns' are provisional truths – undisproven; that's the inherent nature of scientific knowledge.)

The potential for adverse positive feedback loops arising from Public Health Policy measures.

Public health measures, introduced in 2020 on an unprecedented global scale, unleashed many known and unknown unknowns. These measures included 'stay-at-home' lockdowns, widespread temporary business closures, and a decimation of international travel.

The unknowns which I am concerned about here relate to deimmunisation with respect to Covid19 in particular, and towards respiratory viruses in general. (In an earlier article, the dangers of Delta versus the dangers of reduced community immunity, I developed the concept of CRVI – community respiratory viral immunity – as a general measure of communities' immunity towards respiratory viruses. The concept is one of 'co-immunity', whereby immunity to one virus may confer some immunity to others. Cities like London and New York, to survive and prosper, require the highest levels of CRVI. In the biohistory arms race, CRVI must keep increasing if civilisations are to survive.)

We can consider the issue by thinking about 'rings' of immunity. The inner ring represents immunity to a specific pathogen, in our case SARS-COV2 including its evolved variants such as 'Gamma', which devastated South America, and 'Delta', which is devastating Tahiti among other places. Immunity at this 'inner ring' level is boosted by infection and/or vaccination. The former (infection) is more costly to affected individuals than the latter (vaccination) because it is much more likely to lead to serious illness or death. The extent of immunity arising from either process – infection or vaccination – is known to depend on the attributes of immunised individuals (especially age and comorbidity). The key unknown is the extent that immunity to SARS-COV2 diminishes through time.

The next ring of immunity relates to the class of viruses known as 'coronaviruses'. The question here – the known unknown – is the extent to which a general level of exposure to endemic coronaviruses (ie viruses other than SARS-COV2) may confer a degree of immunity to any coronavirus. And the corollary of that question is the extent that reduced exposure to endemic coronaviruses leads to reduced immunity to the Covid19 virus SARS-COV2. The implications of this question are profound: exposure to other circulating coronaviruses could confer a small or medium-size degree of protection against Covid19. And a loss of such exposure could reduce immunity towards both Covid19 and these other 'common cold' coronaviruses; that is, those coronaviruses which we have hitherto taken for granted could become more dangerous. On the bright side, vaccination against Covid19 may well provide a degree of protection against coronaviruses other than SARS-COV2.

Thinking about public health policy in this regard, we need to divide our lived time in a pandemic into emergency periods (when a novel virus is in active circulation), and into non-emergency periods (when the virus of concern is temporarily 'eliminated', or when all eligible people have had the opportunity to be vaccinated). In the emergency periods, policies need to break the chains of infection; eg through lockdowns, distancing, and protective clothing including facemasks. In the non-emergency periods, the policy emphasis needs to be on restoring any immunity that has been lost during the emergency phases; ie people would need to be encouraged to behave in diametrically opposite ways, compared to during the emergencies.

The third ring of immunity relates to other classes of infectious respiratory viruses; for example, influenzas and rhinoviruses. The same question arises here. Could there be a degree of cross-immunity between one class of respiratory virus and another? We do not know; it's another known unknown. And if there is such co-immunity, then, once again, emergency measures (other than vaccination) would be contributing to loss of immunity to the coronavirus of concern, and also to the whole class of coronaviruses. So, ideally, emergency measures should be confined to emergency periods, such as the present Auckland emergency.

The fourth ring of immunity relates to all other immunity-suppression factors caused by public health restrictions. These are known to include socio-economic factors such as inequality, food insecurity and malnutrition. They also include mental illnesses, most likely including stress and ephemeral conditions such as teenage ennui. Indeed, loss of personal autonomy resulting from extended and extensive policy restrictions – and subsequent cultural changes in the direction of infantilisation and agoraphobia – almost certainly facilitates mental health decline.

Can the overuse – especially the extended overuse – of public health policy restrictions induce losses of immunity that outstrip the emergency benefits of these restrictions? If so, a pandemic becomes worse, not better, than it otherwise would be; worse in both severity and duration. If so, we get into a negative feedback loop of the 'race to the bottom' variety; a loop that could accelerate if a civilisation 'tipping point' is reached.

Covid19 Economy Feedbacks

We know that inappropriate economic policymaking can create negative feedback loops of the 'race to the bottom' type. Indeed, an understanding of competitive processes – through what economists call 'game theory' – means that some of these races to the bottom are well understood. I have already cited the example of the Great Depression.

My question here addresses the dichotomy of 'the virus versus the economy'. In New Zealand, the explicit policy position is that the best economic response is the most extensive public health response. The contrast is what has been called the 'light' Swedish approach, which is in effect that the maintenance of a strong economy is also the best public health response. Sweden's Anders Tegnell has repeatedly called the Covid19 pandemic a "marathon, not a sprint".

A third possibility is that neither strategy is correct at their extremes, but that there is an optimal middle ground, in which a strong restrictive public health response should prevail under acute emergency conditions, and that an overtly unrestrictive policy should prevail when a society is not in an acute emergency state. This is indeed the policy approach already suggested, above. (The issue of what constitutes economic success cannot be addressed here; I may note however that the prevailing – and I believe incorrect – financial definition of economic success is essentially the same in the echelons of power in both Wellington and Stockholm.)

The issue is critical in Australia in 2021; it is becoming widely accepted in Australia that an emergency, by definition, cannot be not a semi-permanent state of affairs. To build (and to restore) sufficient immunity to a pathogen, or class of pathogens, a society cannot always be in an emergency state.

Economic decline – however defined, though 'impoverishment' comes close to a good definition – can be an important cause of reduced levels of immunity to diseases. Economic failure may contribute significantly to a loss of 'host fitness' towards micropredators. If a sub-optimal public health policy contributes to economic decline – that could be an unnuanced pandemic response that is either too weak (Sweden) or too strong (New Zealand?) – and impoverishment contributes to population deimmunisation, then a somewhat nasty race to the bottom can take place. Not a race between host and virus. The viruses and other pathogens win when this race starts. It's a race between people and people; between untrusting policymakers and an untrusting precariat.

A healthy economy can facilitate public health. It works both ways.


Public health measures, introduced in 2020 on an unprecedented global scale, unleashed many unknown unknowns. Such policy measures, necessarily, have unintended consequences. One such consequence may be a form of acculturation that may be described as a form of agoraphobia.

If, on balance, extended public health policy measures (and subsequent acculturated voluntary measures) aggravate rather than ameliorate a pandemic, an unfortunate positive feedback loop can arise, with potentially dire consequences. It is not acceptable for policy-makers to be wilfully blind to these possibilities. The big unknown is the rate of – and process of – immunisation loss. We know next-to-nothing about co-immunity. And we actually know far less than we should about the importance of, the history of – and possible reactivation of – our familiar 'common cold' viruses; other branches of public health research, most likely, have been more career enhancing.

In New Zealand, while we necessarily lose natural immunity to coronaviruses during the emergency 'elimination phases' of our fight against 'the virus', we can build some general community immunity from non-emergency exposure to other viruses; some partial immunity that can support vaccination-induced immunity. (Some other countries, which have conspicuously failed in their emergency responses, have actually enhanced their immunity levels, through a mix of natural and artificial immunisation.)

Positive feedback can lead to very negative outcomes. We need to be alert to these possibilities. New Zealand authorities should ensure that they do not overcook public health policies through 'an abundance of caution', and do not acculturate the New Zealand population into a fortress mindset. New Zealand is currently besieged by Covid19. Extended sieges do not end well.


Keith Rankin (keith at rankin dot nz), trained as an economic historian, is a retired lecturer in Economics and Statistics. He lives in Auckland, New Zealand.

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