Herd Immunity vs Eradication Vs Containment Vs Suppression

I have previously posted how every version strategy for dealing with Covid-19 can be considered a form containment strategy. The only variation between strategies is the boundaries of containment. The following rules apply for all strategies:

  • too many cases: increase restrictions
  • few enough cases: reduce distancing restrictions

What changes with strategy is what is considered ‘too many cases’ and ‘few enough cases’.

This page explores the goals of setting levels of containment boundaries higher or lower, and how the four main strategies identified in the title work- or potentially could fail to work.

End Games: The goal of a Strategy.

The goal of any strategy has to be that of managing the virus outbreak, either indefinitely, or until there is an end to the outbreak. There are only two fundamental ways an outbreak ends. Either the outbreak ends because because the virus has been eradicated, or the virus stops spreading because ‘herd immunity’ has achieved, with sufficient people immune to block continued spread of the virus. Why it does not require everyone to become immune is discussed in the curve: basics of a pandemic. There are two ways this ‘herd immunity’ can be achieved, either through people becoming immune following having been infected and then recovered, or through being vaccinated.

Thus the end games are:

  1. Herd Immunity, with people becoming immune by either:
    1. being infected and recovering from infection with immunity
    2. being vaccinated with an effective vaccine
  2. Eradication of the virus

These topics were previously discussed in ‘Endgames‘.

Herd Immunity Strategy.

A ‘herd immunity’ strategy is targeting ‘herd immunity’, by allowing sufficient people to be infected Herd Immunity: Vaccination vs Cases.

The principle is that people who have been infected are then immune. So the more people who have been infected, the more are immune. The more immune people, then the lower the spread rate of infection. This is the principle of ‘herd immunity’. To be effective as a strategy, a significant percentage of the population must be infected.

Implementing a ‘Herd Immunity Strategy’ means allowing infections to take place at the highest rate possible while still ensuring:

  • cases at any one time are low enough that the medical system never becomes overwhelmed and as a result dysfunctional
  • protect the most vulnerable to reduce mortality rates
    • try to bias infections towards those least likely suffer a severe infection

An example would be to set a target maximum case level as using 50% of available hospital capacity prior to the outbreaks, as this leaves a safe ‘buffer’ to cope with unexpected fluctuations in case numbers. The same example could set a target minimum case level at half of the maximum case level. Another approach is to expand hospital capacity to cater with an even higher number of cases.

The goal of this ‘herd immunity’ strategy is enable the progressive removal social distancing measures and restrictions, in response to the rising percentage of the population who become immune following having already been infected, until all restrictions are can be lifted as sufficient people have been infected to achieve herd immunity.

The problem is that the infections required for herd immunity for Covid-19 would result in such damaging health outcomes that it may not even be feasible.

Elimination/Eradication Strategy.

A clear alternative to a herd immunity strategy is an eradication strategy, also called an elimination strategy. Given that people becoming infected leads to serious negative health outcomes, and even deaths, why not try and eliminate infections?

The ‘Eradication Strategy’ focuses on eliminating/eradicating community transmission of the virus.

The principles of an eradication strategy are:

  • continue social distancing/restrictions until there is confidence case numbers will reach a sufficiently low level to use track and trace to eliminate any further cases
  • keep borders closed or well quarantined to prevent introduction of cases from outside.

Compared with ‘herd immunity’, there is less loss of life and far lower medical costs. Perhaps more importantly, some countries have this strategy actually working (e.g. Taiwan, New Zealand).

Elimination/Eradication allows very close to the same removal of all restrictions of living with the virus the ‘herd immunity’ would provide. The two limitations are the need for strictly quarantined borders, and effective testing and vigilance for any new virus cases.

Critics say that there is never true ‘elimination’ if people can travel still travel to the country at all, and it is true that such arrivals continue to require strict and vigilant quarantine.

Containment/Suppression Strategy

The common endgame goals and logic.

Both ‘containment’ and ‘suppression’ mean ‘keeping cases within boundaries determined as acceptable’. Neither trying to eradicate infections completely, nor allowing sufficient infections as to achieve herd immunity as people become immune following being infected.

Straddling the endgames of herd immunity strategy and eradication strategy, effectively leaves containment (or by another name, suppression) without an ‘endgame’.

The endgame is to assume a vaccine will provide an endgame, thus the strategy requires no endgame of its own.

A vaccine can provide ‘herd immunity’ without requiring the suffering of a ‘herd immunity’ strategy, and since eradication is not required, the goal is for less significant lockdowns than required than with an eradication strategy.

Naming: Containment Or Suppression?

Early in the outbreak, Australia used the term ‘Containment’ to describe a strategy where cases could be kept below an acceptable limit by applying measures until the growth of cases was close enough to 1.0 rising levels of immunity would see growth soon drop below 1.0 and measures could then be relaxed as immunity progressed towards herd immunity levels.

The difference between the usage of the two terms being that ‘containment’ is taken to mean achieving keeping cases below the upper threshold without requiring lockdowns to be successful in reducing case numbers, as per the original ‘flatten the curve’. Most countries being certain case numbers are no longer rising, without having case numbers fall, as impractical and risky.

Tthe point where case number fall. have found that trying to achieve lockdowns that stop growth in case numbers, but It was soon found trusting spread rates to fall without the use of lockdowns was too risky.

Australia, and some other countries, labelled this use of aggressive lockdowns to achieve containment as ‘suppression’, which is to keep the curve flat as described previously by introducing lockdowns when required to prevent case number rising above required limits.

Reality is, what Australia and some other countries now call ‘suppression’, was always the only viable way to achieve containment, and contain cases within practical limits with Covid-19. So Suppression and Containment become the same.

Containment/Suppression Vs Eradication.

Containment differs from eradication in the following ways:

  • some predefined level of community infection is considered ‘acceptable’
  • restrictions/social distancing measure to keep spread at an average of approximately 1.0 must remain in place.

Tolerance for community infections continuing, means social distancing and restrictions can be relaxed without waiting for case numbers to drop as low as with eradication, but the penalty is that not all restrictions can be removed. Ever. While there are community infections, without herd immunity or lockdowns and restriction, case number of Covid-19 grow exponentially. Short of herd immunity (which may be not possible anyway), or eradication, social distancing restrictions will be required to prevent case numbers skyrocketing.

The problems with Containment/Suppression

There are number of common misconceptions or myths which tend to make the containment/suppression strategy less economically efficient than eradication, while at the same time incurring a greater loss of life.

1. Understanding ‘it is not over!’

As discussed in the CNN Myths article, many people perceive that relaxing of restrictions can progress to the same low levels as with eradication, even without eliminating all community spread, and this is simply not possible. If there are cases, without herd immunity, the case numbers will again rise in the absence of sufficient measures.

2. Averted Threat Denial

In a containment phase following a lockdown, the perception often arises that the cases and deaths seen under lockdown was experiencing the full threat faced by an outbreak. “Why bother with lockdowns if we have seen all the threat there is?”

3. Too Much Sickness & Death

The third problem is that over the course of the pandemic, hospitalisations and deaths continue. If a treatment is slow in arriving, the toll on society is far more significant than with eradication.

Conclusion.

The strange thing is, Sweden followed a ‘herd immunity’ strategy because it should be better economically.

Most other countries follow a ‘containment/suppression’ strategy because an elimination strategy is seen as having too high an economic cost.

Taiwan, New Zealand, Iceland, Vietnam (and if data is accurate, China) are some of the rare examples of elimination. These countries (China aside) have had the lowest economic cost, as well as very few deaths.

The policy usually rejected for economic reasons, has the best economic results as well as the least deaths.

One thought on “Herd Immunity vs Eradication Vs Containment Vs Suppression

Add yours

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Blog at WordPress.com.

Up ↑

%d bloggers like this: