Herd immunity- How feasible?

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Topic: General Studies 2,3:

• Issues relating to development and management of Social Sector/Services relating to Health

In News: WHO has strongly refuted the idea of herd immunity to fight covid-19 saying that it has never been used as a strategy to respond to an outbreak in the history of public health, let alone a pandemic. Tedros Adhanom Ghebreyesus, Director-General of WHO has termed herd immunity as scientifically and ethically problematic.

What is Herd Immunity?

• Herd immunity is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune.
• Initially, herd immunity, an important tool in epidemic control, was proposed as a means to overcome the pandemic. 
• Only a certain proportion of the population needs to be infected in order to stop large outbreaks, either through naturally-acquired disease, or through vaccination. 
• Since a vaccine is not available for COVID-19 yet, some people advocated that the infection be allowed to spread in the community until herd immunity is achieved.

Why is this being stoutly opposed?

• The SARS-CoV-2 virus is easily transmissible and would require around 60-70% of the population to be infected to acquire herd immunity.
• If we allow this to happen naturally, it will take a long time, of course, but more importantly, it is going to do a lot of collateral damage
• So, even if 1 % of people who get infected are ultimately going to die, then this can add up to a huge number of people, if we look at the global population
• Herd immunity is not a strategy or a solution by some but is considered as surrender to a preventable virus

How and when will herd immunity be achieved in this pandemic?

• Herd immunity is achieved when one infected person in a population generates less than one secondary case on an average 
• This corresponds to the effective reproduction number R (that is, the average number of persons infected by a case) dropping below 1 in the absence of interventions
• With flu pandemics, herd immunity is usually attained after two to three epidemic waves, each interrupted by the typical seasonality of influenza virus, and more rarely, by interventions
• Currently, there is insufficient confirmed information on re-infection to determine how that will influence the pandemic’s course.

What does the sero-prevalence study in India say?

• A measure of the infection levels in the population is provided through the sero-surveys conducted by the Indian Council of Medical Research (ICMR). 
• The second study was done between August 17 and September 22, 2020, and found the prevalence at 15.6% of the population in urban slums and at 8.2% in non-slum areas. The hotspots were not included this time.
• In Delhi, the second round estimated a sero-prevalence of 29.1%. The study revealed that for every reported COVID-19 case, there were 26-32 infections, down from 81-130 infections per reported case in May

However, it doesn’t always guarantee protection against any disease-

• It was mistakenly assumed that as this disease spreads across the world, only the severe cases become apparent while most people would indeed be infected as reflected in sero epidemiology results. Greater proportion of people getting infected would mean that the pandemic will be over soon and people can go back to normal business. 
• But the preliminary results from in sero epidemiology studies are showing the opposite. The proportion of people with significant clinical illnesses is a higher proportion of all those who have been infected. This is because the number of people infected in the total population is probably much lower than we expected as per World Health Organisation. 
• Other challenges like some people do not seem to develop a humoral immune response, relationship between antibody response and clinical improvement is still not clear, mild infections can resolve even before detectable antibodies are produced, how long neutralising antibodies against the virus would last is currently not known.

What is “Focussed Protection”?

• Based on the concept of herd immunity
• The most compassionate approach that balances the risks and benefits of reaching herd immunity, is to allow those who are at minimal risk of death to live their lives normally to build up immunity to the virus through natural infection, while better protecting those who are at highest risk.
• World Health Organisation said herd immunity was “scientifically and ethically problematic”. It said countries must continue to do what they have been doing to deal with the pandemic, only more effectively. 

Conclusion

In the absence of a vaccine or drug, and without a clear understanding of the disease pathology, seeking to achieve herd immunity through infection is a dangerous strategy. Allow the disease to spread too quickly, it overwhelms the health system and causes many people to die “unnecessarily”; do it too slowly, and it takes that much longer for life to come back to “normal”. Therefore, for almost all countries, at this juncture, it is a cruel choice between saving lives and saving livelihoods.

Note: The prominent novel coronavirus subtype found in India: A2a strain of SARS-CoV-2

MUST READ: Vaccine Nationalism

Connecting the Dots:

1. What is herd immunity? How does it get developed? How does it provide protection from viral infections? Illustrate.
2. Herd Immunity is scientifically and ethically problematic. Why?
3. Essay: Herd Masking and Herd Immunity