What the herd!

The criterion of truth is that it works even if nobody is prepared to acknowledge it

Ludwig Von Mises

Photo credit: Mark Chadwick – http://www.markchadwick.co.uk/

The phrase “herd immunity” has acquired such a negative connotation that it has become almost impossible to look at it objectively. Let’s try to get to the very bottom of it and see it from a neutral standpoint.

Is herd immunity a process that can be used as a strategy? No

‘Herd immunity’ is a description of a particular state. It is merely a descriptive concept. You cannot use such a concept as a tool to plan a strategy or to influence the course of nature. It is a state in which the spread of the infection in the community slows down from an epidemic rate to become an endemic disease due to development of infection specific immunity in our body.

The term ‘epidemic’ describes a phenomenon of increasing infection rate in a community. During epidemic of an infection, each infected person spreads the disease to more than 1 person. In such a situation the disease will gradually increase in number with time. Mathematically, if this is plotted against time it will have an exponential curve. However this will not continue forever. It will eventually starts to slow down and then achieve a state of equilibrium. The whole thing is like a chemical reaction between two reactants, the process continues until they reach a state of equilibrium. Knowledge about this reaction can potentially shift the final state of equilibrium in our favor.

What slows down the spread of the infection in a community?

As the pathogens spreads through the community, individuals in the community will either get sick and/or develop immunity to the infection. As the number of people who have developed immunity increases, the pace of spread will start to drop. Eventually this interaction between man and virus comes to a state of equilibrium. In this state infected people on an average infects one or less than one person and such an infection is called an endemic infection. In this situation, the disease is still present in the community in few individuals but it is not spreading at an exponential rate.

This state of equilibrium in which the epidemic disease becomes endemic happens when the herd immunity is achieved. A state in which a majority of the populace have developed immunity against the virus. This is the natural course of events that will happen if we do not have knowledge regarding mechanisms that influences the balance of this equilibrium. In this situation, neither the virus nor the humans are eliminated. However during this interaction, depending on the type of the virus, there is a risk for serious complications among the infected individuals. Some people could also die if this process is allowed to progress in its course.

What are the mechanisms that could change the course of these events and influence the final equilibrium state (herd immunity)?

Antiviral – If there is an antiviral molecule then such a substance would treat the infection and prevent the pathogen from causing complications or death. Even in this situation, the medicine would not affect the rate of spread of the infection or the number of people who is going to be infected during an epidemic spread. It can only help us to treat the infection once it has happened. And also this medicine will not change the time at which the equilibrium point will happen(transition from epidemic to endemic). Thus, if we have the required knowledge to make an effective antiviral when a new virus is spreading through a naive population, then this medicine would have changed the following events in the natural course of things

  1. It will reduce the number of deaths at the end of the epidemic
  2. It will reduce the number of hospitalizations at the end of the epidemic
  3. No significant effect on the time point at which this epidemic will end
  4. No significant effect on the number of people who would have gotten infected by the time the epidemic ends

Vaccine – Vaccination works by injecting a portion of the virus particles inside our body. Such particles don’t cause infection or disease but it will stimulate our immunity similar to a real infection. The body would respond as if there was an infection and mount antibodies against it. If this injection is administered to a population when a new virus enters the community, then this vaccine would have changed the following events in the natural course of things

  1. It will reduce the number of people who would get infected when the epidemic ends. This is because a majority of them will already have antibodies even before the virus could infect them. In this way, vaccination can shift the center point of equilibrium in favor of the humans.
  2. It will affect the time point when an epidemic will end. Vaccination will shorten the duration of the epidemic by making very little people available for the virus to infect.
  3. There will be less deaths and less hospitalizations

With COVID, we do not have any effective antiviral that could kill the pathogen. We do not have any vaccine that could artificially stimulate the antibody or immunity production at this point in time. In short, we do not have any knowledge about mechanisms that strongly influence the natural course of events in favor of humans. If we face this virus with this knowledge base, then the events will unfold as it is. Without having a vaccine we cannot influence the number of individuals who will need to be infected for an epidemic to end.

Then what is the role of social distancing, lock down, case isolation and contact tracing methods?

Pathogens like coronavirus that are shed in human oral or respiratory secretions can spread easily due to community living. If we were to live a solitary life in the forest with only rare contacts with other human beings then such a pathogen will not be able to establish an epidemic in humans. The success of these respiratory viruses is due to our social life. Community with dense population and networks of human interaction will have a high rate of transmission. In such a situation a higher proportion of the community members must carry immunity to break the spread of the virus. When interventions like social distancing, universal masking and respiratory hygiene are implemented, the transmissibility of the pathogen drops. The following changes will happen in the natural course of events

1. It will shift the equilibrium in our favor and reduce the number of people who would get infected when the epidemic ends.

2. It will slow down the rate of infection and could also end the epidemic sooner by reaching a point where an infected individual infects less than one other person due to heightened respiratory hygiene among the community.

3. However these interventions must be followed as long as the pathogen is present in the human population. Once the strategies are relaxed, the equilibrium will shift towards the original point if the reaction were to happen at a ‘natural’ rate.

Each community based on the complexity of their social milieu, should identify respiratory hygiene measures that can be sustainably followed at least until a vaccine becomes available.

There is always something more to do, we are only limited by how much we know. There is always something more to know, we are only limited by how much we can imagine.

With our current knowledge, the only thing we could potentially influence is the rate at which this virus spreads through the population. We don’t have a choice with regards to herd immunity. Herd immunity is the final state of equilibrium in all strategies. Other important intervention that could be practiced, if we all agree upon that herd immunity is the final state, is to prevent vulnerable people from getting infected during the epidemic phase. This can potentially reduce the complication rates, hospitalization and deaths.

If slowing it down is the only option then to what extent should we slow down the rate of spread of this virus?

  1. Depends on the hospital capacity
  2. Depends on how much and how long the society can handle restrictive measures without losing the livelihood and dignity of the populace

Our fight should be proportionate to the knowledge we have about the process. We would incur more losses if we get into a fight without knowing the limitations of our strategies.

6 thoughts on “What the herd!

  1. Good article in simple explanatory terms. Given that herd immunity is not a strategy in itself, it seems it will take few months to achieve this state. Will hope for the best.

    Liked by 1 person

    1. Highly informative article. Language lucid and a layman can understand the medical terms.

      May I add that the social distancing concept, protecting hands, feet, nose mouth( gargling)and face I.e. becoming aware of health and hygiene — was practiced in Asia through courtyards in Indian subcontinent, , Mexico and up till Greece .
      People had to wash feet before entering place of worship in all religions;

      Mother and baby isolated when an infant born fir 10 days; A person lighting pure to departed soul isolated( quarantined) for 10 days and outsiders partaking food in the house of dead after 14 days, sweepers and workers who did scavenging job prevented entry for. Mai. Door of the house, their vessels fir eating food kr beverage either made of clay or leaves- discarded immediately…

      Amazing and scientific truths bankrolled in religious practice by the Rishis of yore!

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  2. Thank you sharing these concepts in simple terms. One take away for me is – to keep the social distancing for much longer than normal population, especially for people with vulnerable pockets at home.

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    1. That is true. Even once the epidemic phase is over we need to learn new tricks to adapt our ways to live with endemic covid infections in the community and host of influenza viruses. We must continue the general respiratory hygienic measures that were learnt during this pandemic. Identify and implement simple practices that we can do forever.

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  3. Density is the key. In forest there is diversity. Homogeneity factors breed problems. In framing as well we have to resort to measure of disease control.

    Like

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