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What is Herd Immunity? Why is it Important? And Is it a Strategic Option in India’s Fight Against Coronavirus?

Aug 14, 2020 7:06 PM 4 min read

Heard of Herd Immunity? Sorry.

It’s been over seven months now that the first case of the deadly virus was reported in China’s Hubei district in Wuhan. Lockdowns have been imposed, lifted and re-imposed across the globe. But with the number of cases registering a new high every other day, the end is nowhere in sight. 

What’s the cure? Up to date, no specific antiviral drug or treatment has been testified or globally recognized as being effective in treating COVID-19 patients.

Prevention is better than cure: While the development of a potential vaccine has gathered pace, with Russia announcing that it has approved a vaccine and others like the US striking a $1.525bn deal with Moderna, a US-based biotech company, for securing the supply of 100 million doses of the novel coronavirus vaccine that the company is developing, scepticism around rushed trials persist.

Amidst all these deliberations of a potential strategy to combat the coronavirus, there has risen the discussion around “herd immunity”. 



What is Herd Immunity? Why is it Important? How Does it Work?

Herd immunity or community immunity is a stage of an epidemic when a virus ceases to spread easily because enough people are immune to it. 

This can happen in two ways:

  1. A large chunk of the population contracts the disease, and over time, builds up an immune response to it (natural immunity)
  2. Rampant vaccination to achieve immunity


When Does a Community Attain Herd Immunity? 

This depends on the reproduction number, or R0, pronounced “R-naught,”. The R0 essentially represents the average number of people that an individual with a given virus is likely to infect. The higher the R0, the more people need to be resistant to reach herd immunity.

But it is a deceptively complex number to arrive at and constantly changes, given that it is determined by researchers using a number of different and fluid sociological, economic and environmental factors. And as a result, it is often written as a range, rather than a single number.  

As per researchers, this number for the coronavirus is often touted as between 2 and 3, meaning each infected person has spread the virus to an average of 2 to 3 people. This implies  that 50%-67% of the population would need to be resistant before herd immunity kicks in and the infection rates start to go down.

Moreover, “when a large percentage of the population acquires an infection, depending upon the nature of the pathogen it may or may not develop immunity. The immunity may be permanent or temporary,” said  public health expert Imrana Qadeer in an interview with HuffPost India. 


What is Herd Immunity? Why is it Important? And Is it a Strategic Option in India’s Fight Against Coronavirus?


For instance, data from Spain - a country that has reported community transmission - shows that only an estimated 5% have developed antibodies in response to the virus. 

Food for Thought?: According to a study published in the Journal of the Royal Society of Medicine, Sweden’s strategy of letting the infection spread in a controlled manner in order to achieve herd immunity has failed. Unlike most other countries, Sweden did not impose a strict lockdown, and relied on its citizens’ individual responsibility to curtail the spread of the virus. The health authorities earlier predicted that 40% of Stockholm’s population would have had the disease and acquired antibodies by May 2020. However, results from a recent sero surveillance study showed that only 15% of the country’s population has developed antibodies. Moreover, compared to other European nations, Sweden has higher infection numbers, hospitalisations and death rates.

In addition to this, as per a study conducted by the Chongqing Medical University, China, people who had recovered from the COVID-19 disease showcased a sharp decline of up to 90% in the antibodies within the time frame of 2-3 months.


Herd Immunity in India

A serological survey conducted in Delhi between June 27th and July 10th found the presence of coronavirus-specific antibodies in about 23% of the samples tested. The results of that survey are being interpreted to suggest that Delhi could be approaching herd immunity.  

Meanwhile, a survey undertaken in Mumbai - with special focus on the slum areas - estimated that 57% population in three wards have developed antibodies against the novel coronavirus disease.



But Does the Presence of Antibodies Ensure Immunity?

The mere presence of antibodies does not mean that the person is protected against the disease. What is important is the amount of antibodies present, and whether these also include “neutralising antibodies” - the ones that actually fight the disease. 

FYI: Serological surveys are only designed to test the presence of antibodies. Neither do they assess the quantity of antibodies nor detect the presence of neutralising antibodies.

It is also important to note here that herd immunity might have been observed in smaller pockets of the country, particularly in the hotspot zones with high population density, but a countrywide herd immunity still remains too long a shot.


Is Herd Immunity a Strategic Option in India’s Fight Against Coronavirus?

“In a country with the size of the population like India, herd immunity cannot be a strategic choice or option. It can only be an outcome, and that too at a very high cost as it means lakhs of people will have to be infected, get hospitalised and many will die in the process,”  said Rajesh Bhushan, Officer on Special Duty in the Ministry of Health, at a press briefing last month. He added that herd immunity can only be achieved through immunisation in India but that is in the future.

Considering all their caveats, the wiser, more practical and more feasible course of action would be to continue practising social distancing, sanitation, hygiene and other preventive measures until a vaccine is officially announced and is within reach. 


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