Herd immunity
Dr. Ajay Jain
Jun 4, 2020
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Role of Herd immunity in control of COVID-19
What is Herd immunity?
Before we start first you should know “what is herd immunity”. Herd immunity is an epidemiological concept that describes the place where a population is sufficient immune to a disease that the infection will not spread within that group, either through vaccine or natural immunity after getting infected with disease.
For example mumps is an infectious disease. It’s very uncomfortable and sometime cause life-long complications. It is also vaccine preventable, with high effective vaccine that has made this disease very rare at present. Mumps has basic reproductive rate of 10-12, which mean in a population where all are not immune to this disease and if one person get infected by mumps then he will spread disease on to 10-12 other people. This mean that without vaccination roughly 90 to 95 percent people will get this disease but there is still 5-10 percent people will not get sick because once everyone else is immune there is no one to catch the disease from.
In the other hand we can increase that number by vaccination, because vaccination make people to immune to infection and also stops infected people passing the disease to other people. If we get enough people to immune then we can stop the spreading of disease.
Herd immunity is disease specific and also influenced by the ease with which the disease spread through person to person. The specifics about coronavirus and herd immunity still not clear. It will take a long time to achieve worldwide herd immunity. It may take less time in some places but it will take time.
So there are two ways to achieve Herd immunity. First one is either a large population gets infected with disease or a protective vaccine for develop immunity for that disease. And based on early estimate of the coronavirus infection we will likely need at least 70% of the population to be immune to have herd immunity.
Herd immunity regarding coronavirus is”NOT a Good Idea”:
So achieve herd immunity regarding coronavirus in present time is getting infected with disease and then get immunity but if we do not follow physical distancing and other protections, the virus can infect many people within few months. This would be overwhelmed our hospitals and lead to high death rates.
Some other disease like chickenpox before the varicella vaccine was developed; some people exposed themselves intentionally to get infection and then immunity for this disease. But SARS-nCoV-2 is very different because it has much higher risk of severe illness and even death.
The death rate of corona virus is still unknown but according to current data it is 10 times higher than normal flu. Although it’s higher still in weaken immune people like elderly and people with already have major diseases like hypertension, COPD, asthma, Diabetes which makes immune system weaker. But it is best to avoid overwhelming our hospitals and doctors.
Other viruses like flu is changing over time, so antibodies from a previous flu infection provide protection for a limited time like a month or a year. If SARS-CoV-2 that causes COVID-19 is like other flu viruses then we can expect that people will get immunity for a limited time period like a month to year but maybe not for entire life.
In the best way, we maintain current levels of infection or even reduce these levels until a vaccine available. This will good effort on the entire population with continued physical distancing for a period of time like a year or longer before a highly effective vaccine developed, tested and mass produced.
The other way of getting herd immunity with get infection with disease is not a good idea right now regarding coronavirus like those we have seen in place like New York City. The physical distancing may vary over time and will not always need to be strict as our current situation but unless we want millions of people get infected with coronavirus, life is not going to completely normal again until a vaccine can be developed and widely distributed. So before the vaccine, practicing herd immunity is not safe for population.
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