(Daily News Scan - DNS English) HERD Immunity : A Ray of Hope
In the previous week the UK government’s chief scientific adviser Sir Patrick Vallance communicated about a strategy that would permit the novel corona virus to infect 60% of the country’s population so that a degree of “herd immunity” could be achieved.
In this DNS we will understand what is the herd immunity? And also some other information associated with it.
What is Herd Immunity?
Herd Immunity basically refers to preventing an infectious disease from spreading by immunising a certain percentage of the population. This concept is commonly used in cases of vaccination.
The idea behind this concept of herd immunity is that, if a certain percentage of the population is immune, members of that group can no longer infect another person. This breaks the chain of infection through the community (“herd”), and prevents it from reaching those who are the most vulnerable.
This scientific principle behind this concept is that the presence of a large number of immune persons in the community, will interrupt the transmission, providing indirect protection to those who are not immune. The epidemiologists use a measure called the ‘basic reproductive number’ (R0). This will estimate the extent of spread and immunity. It will indicate how many persons can be infected when exposed to a single case; an R0 of more than 1 indicates one person can spread the infection to multiple persons.
Some of the scientific evidences reveal that a person with measles can infect around 12-18 persons; and a person with influenza can infect around 1.2-4.5 persons, depending on the season. On the basis of the available evidence from China, and according to various experts, R0 of, COVID-19 ranges between 2 and 3.
There are three ways through which an infection can spread in a community.
- The first - looks at a community that is not immunised. When two infectious cases, both with an R0 value of 1, are introduced, there is a possibility of the entire community being infected, with a few exceptions.
- The second - there may be some persons who have been immunised; and only these immunised persons will not be infected when at least two infectious cases are introduced in the community.
- The third - there may be some persons who have been immunised; only these immunised persons will not be infected when at least two infectious cases are introduced in the community.
There are multiple factors on which we can decide that a community has achieved herd immunity. It depends on concepts like how effective the vaccine for a given disease is, how long-lasting immunity is from both vaccination and infection, and which population’s form critical links in transmission of the disease.
Mathematically it is defined by, on the basis of a number called “herd immunity threshold”, which is the number of immune individuals above which a disease may no longer circulate. The higher the R0, the higher the percentage of the population that has to be immunised to achieve herd immunity.
To allow a large part of the community to get infected by this COVID-19, is very risky. This kind of strategy is dangerous and associates many unknown facts. There is still not many information and known facts available about the behaviour of the pathogen. It can take months to build group immunity against COVID-19. The basic need is to protect people who are at greater risk; especially the people above the age group of 55 and those with cardiovascular disease and hypertension, are the most vulnerable. There is still not any surety about the COVID-19, we don’t know whether one can become immune to the virus. Nor is it clear whether a person who develops immunity will remain permanently immune.
