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Is ‘Herd Immunity’ Really an Effective Strategy Against COVID-19?

Herd immunity helps break the cycle of transmission in contagious infections. But will it work against COVID-19?

Updated
Health News
4 min read

Video Editor: Ashutosh Bhardwaj & Varun Sharma

Video Producer: Hera Khan

Countries around the world are designing and implementing strategies to mitigate the spread of the novel coronavirus and to bring down the cases of COVID-19, the disease it causes.

While social distancing, heavy lockdowns and intensive testing are helping some to contain the virus, UK has come into the limelight for reportedly hoping to acquire ‘herd immunity’ as it enters the 'delay’ phase of response against the pandemic.

But what exactly is herd immunity and is it an effective approach in dealing with a pandemic such as this? Let’s break it down one at a time.

Herd Immunity Breaks the ‘Cycle of Transmission’

FIT spoke to Dr Sumit Ray, a critical care specialist in Delhi NCR, who explained, “Once more and more people are exposed to an infection, mostly a viral infection, they either build immunity for it or they succumb to the disease.”

“If a larger number of people build up immunity, the transmission rate goes down and there’s a drop in the level of cases and deaths, bringing down the overall severity of the disease. This breaks the cycle of transmission.”
Dr Sumit Ray

This is because when people build immunity against a virus, they not only are protecting themselves against it, but also are preventing themselves from becoming carriers of the disease and transmit it to someone else.

In a more basic sense, the concept of herd immunity can be understood when we talk of vaccination. Vaccines provide immunity against particular viruses or bacteria by exposing the body to their weakened versions in quantities which don’t make a person sick. By fighting the antigen once, the body is prepared to face it again, and subsequently, builds immunity against it.

In the case of vaccination, it is believed that if the majority of children are vaccinated, even those who haven’t been vaccinated (or can’t be for medical reasons) will get protection against the particular virus.

This is how WebMD explains the phenomenon: When lots of people in an area are vaccinated, fewer people get sick, and fewer germs are around to spread from person to person.

<i>People are shown as circles. Infectious agents (germs) spread between the people in orange, although they do not get severe disease. When the infection reaches people who are highly susceptible (red) they get the disease and can be very sick or die.</i><i>In the lower panel, the people in green have been vaccinated. This now protects those in yellow as well, who had previously got the infection and possibly the disease. Although the figure only shows a few people being vaccinated, in reality many people have to be vaccinated for herd immunity to work.</i>
People are shown as circles. Infectious agents (germs) spread between the people in orange, although they do not get severe disease. When the infection reaches people who are highly susceptible (red) they get the disease and can be very sick or die.In the lower panel, the people in green have been vaccinated. This now protects those in yellow as well, who had previously got the infection and possibly the disease. Although the figure only shows a few people being vaccinated, in reality many people have to be vaccinated for herd immunity to work.
(Photo: University of Oxford)

But for this to work, a very large proportion of the population has to get vaccinated, and the more contagious a disease is, the higher this number needs to be. For instance, a disease like measles would require at least 90-95% of the population to be vaccinated in order to achieve herd immunity.

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Is Herd Immunity an Effective Strategy Against COVID-19?

According to an ITV report, the UK government aims to mitigate the impact of COVID-19 by allowing the virus “to pass through the entire population so that we acquire herd immunity, but at a much-delayed speed so that those who suffer the most acute symptoms are able to receive the medical support they need, and such that the health service is not overwhelmed and crushed by the sheer number of cases it has to treat at any one time”.

Speaking to FIT, Dr Sumit Ray says that hoping to achieve herd immunity in an uncertain scenario such as this, when knowledge is still evolving about the novel coronavirus, its transmission rate, or whether there will be a ‘next season’, seems “drastic”.

“It cannot be an immediate strategy. It takes time, and by the time it actually works (if at all it does), we would have lost many lives.”
Dr Sumit Ray

For a disease like COVID-19, where we do not have a vaccination, the process of acquiring herd immunity would need a considerable number of people to be infected and to recover.

This depends upon the contagiousness of the disease, which for COVID-19, is around 3.28 so far (the number of cases that a single case generates - will probably change with more studies). According to an article published in The Conversation, this would mean that about 70% of the UK population would need to be immune to COVID-19. Considering the current fatality rate of 2.3%, more than a million people would have to die and almost eight million would be severely infected and would need critical care.

While there’s still not much clarity on whether the UK government plans to implement the strategy, even the best-case scenario, where the most vulnerable population is protected, would lead to more than 236,000 deaths.

In fact, Anthony Costello, former World Health Organization director, tweeted that such a strategy could be in conflict with WHO’s policy of containing the virus by tracking and tracing all cases. He expressed doubt over the efficacy of a ‘lasting’ herd immunity and said, “Does coronavirus cause strong herd immunity or is it like flu where new strains emerge each year needing repeat vaccines? We have much to learn about Co-V immune responses.”

“Vaccines are a safer way to develop herd immunity, without the risks associated with the disease itself. Is it ethical to adopt a policy that threatens immediate casualties on the basis of an uncertain future benefit?”
Anthony Costello

The aim, therefore, needs to be to minimise transmission and to bring down the number of infected cases to as low as possible, which is what other countries are trying to do. Social distancing, vigorous testing and contact tracing are of key importance, especially in India, where the country is still in the ‘local transmission’ phase.

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