There are three scenarios in which an infection spreads within a community, if the assumption is that only one person would be infected by being exposed to a single case.
Herd immunity: The UK’s Chief Scientific Adviser, in March, indicated towards a strategy to allow the SARS-CoV-2, the coronavirus causing COVID-19, to infect as much as 60% of the population of the country, in order to achieve a certain level of herd immunity, according to a report in IE. However, the government had to retract the statement and look towards the self-isolation of the elderly as the idea was criticised widely, the report added.
Herd immunity: What it means
Herd immunity is a method through which an infectious disease is contained by immunising some portion of the population. While the concept is usually used with regard to vaccinations, if enough people have become immune to the disease after the disease outbreak, that would also lead to herd immunity. The concept behind herd immunity is that it breaks the chain of the disease as people who have become immune to it can no longer be infected by it. This way the disease is unable to spread through the community or the “herd” and hence, the most vulnerable sections of the society could remain safe.
However, according to the IE report, the UK was not going to fight COVID-19 based on this definition of herd immunity. It was instead planning to expose the entire population to the disease and let the majority of them develop immunity to it.
How does herd immunity work?
According to an IE report, there are three scenarios in which an infection spreads within a community, if the assumption is that only one person would be infected by being exposed to a single case.
In the first scenario, if the community is not immunised, and two cases are introduced, there is a possibility that the entire population would contract the disease, with a few exceptions.
In the second scenario, where some people may be immune to the virus, only these immune persons would remain protected from the disease.
In the last scenario where the majority of the population is immune to the infection, the spread of the disease would be limited to the vulnerable groups. In fact, in such cases, even the vulnerable groups would be protected by the immune persons acting as a barrier.
Herd immunity against COVID-19: Why is it questionable?
Allowing a large number of people to be infected with COVID-19 at such a stage is very risky, experts have said, as the strategy would be based on many unknown factors, the IE report stated. One of the reasons for this is that the pathogen is still widely unknown to the researchers and it is also not clear how many people a single case can infect. Moreover, building a herd immunity could take months, and the priority of the countries should be to protect its vulnerable population from the disease immediately.
Moreover, since not much is known about the pathogen, it is not clear whether immunity can be developed to the virus or not. It is also not known if a person can remain permanently infected by the virus.