Thursday, May 21, 2020

What is herd immunity and how it works?

According to Merriam Webster, herd immunity is a reduction in the risk of infection with a specific communicable disease (such as measles or influenza) that occurs when a significant proportion of the population has become immune to infection (as because of previous exposure or vaccination) so that susceptible individuals are much less likely to come in contact with infected individuals.

Clearly, the implementation is as follows. If 80% of the population is immune to the virus, four out of five people who meet someone who has infected will not get sick, nor will they spread the disease further. In this way, the spread of infectious diseases can be controlled. Depending on how contagious infection is, usually 70% to 90% of the population needs immunity to achieve herd immunity.

The term herd immunity or also known as herd effect, community immunity, population immunity, or social immunity is now prominent when the global Covid-19 pandemic struck all parts of the world. Various media wrote that herd immunity was used as one of the strategies in tackling the spread of the Coronavirus. Of course, many pros and cons accompany the issue.

Let us learn from the Zika virus case that we cited from the MIT Technology Review page. Zika virus became epidemic in 2014, where the disease was transmitted by mosquitoes which caused birth abnormalities.

Two years later, in 2017, the disease is not a threat to worry about. A study in Brazil found by examining blood samples that 63% of the population in the northeastern seaside city of Salvador had been exposed to Zika, so researchers speculated that herd immunity had overcome the outbreak.

A vaccine is also a factor that creates herd immunity, both when given broadly or when given in a "ring" around new cases of rare viral infections. That is the way diseases such as smallpox were eradicated and how polio is close to being removed from the face of the earth.

But remember, the cases above can be resolved because the vaccine has been found, or at least there is already empirical data about patients who are already immune. In the Covid-19 case, various vaccine efforts are underway, but many predict that the vaccine will not be available for more than a year.

Even then, if vaccine makers can find it, they lose the race by natural means of protecting the first infected herd. That is what happened in 2017 when drugmaker Sanofi quietly left the Zika vaccine development project after running out of funds, or in other words the market no longer needed it.

The problem is, Coronavirus is a new type, so there is no evidence that people who have recovered are immune to it. This is what makes Covid-19 spread and why it can have very severe effects on some people.


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