Is herd immunity the answer for all our problems?
#17 - Herd immunity can be achieved only through vaccination
Our strategy for District Magistrates in India: COVID-19 is a war only Districts can fight.
Herd immunity is not a prevention policy to stop a pandemic! When most people in a population are immune to a disease, the population is said to have herd immunity.
In the figure below — we see that when most people are susceptible, a few infected people can spread the disease (top panel). On the other extreme (bottom panel), when most people are immune, even the susceptible individuals are protected from infections.
Why does it work?
Because every individual interacts with only a few other individuals. It is highly unlikely that a susceptible person will come in contact with an infected individual.
Rinderpest and Smallpox are two diseases that have been eradicated by building herd immunity. Efforts are on to eradicate polio and measles in the same way.
Herd immunity for these diseases was developed through mass vaccination campaigns.
Covid-19 vaccine will take at least 12-18 months to develop! The only option is early detection and prevention.
COVID-19 and Herd immunity
In the early days of the pandemic, the United Kingdom had resorted to a strategy of building herd immunity through infections, instead of lock downs and social distancing. It involved infecting young people (who have a lower mortality rate from the virus) to build herd immunity and protect the rest of the population.
This strategy was immediately and widely condemned by scientists. Some have suggested that this can be used in India!
Why will herd immunity through infections not work?
The fraction of people that need to be infected to be ‘herd immune‘ is unclear as it depends on the reproductive number of the virus, whose estimates are very uncertain. Current estimates say that 65-85 % of the population will have to be immune. [Article]
If 65%-85% of India’s population is infected, with a death rate of 3.4 % we are looking at 30 - 39 million deaths in India.
The long term effects of the virus on the body are not entirely known yet, there are preliminary reports of neurologic issues and lung damage. In the face of such a massive risk, it is foolish to pursue herd immunity through an infection strategy.
It is unknown if the immunity developed from infection is sustained in the body. It is possible that infected and recovered individuals may become susceptible again.
It is extremely hard to develop a foolproof strategy where only young individuals will get infected while sheltering the elderly.
Bottom Line : The best strategy forward is to maintain social distancing and lock downs until a vaccine is developed.
Herd immunity through mass infections is an irresponsible strategy involving a colossal risk of millions of deaths!
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