Herd immunity and Corona virus,हर्ड इम्यूनिटी क्या है,कोरोना और हर्ड इम्यूनिटी

Herd immunity and Corona virus,हर्ड इम्यूनिटी क्या है,कोरोना और हर्ड इम्यूनिटी

Herd immunity is known by many names like herd effect,community immunity,population immunity, social immunity.

Now a days corona pandemic has been a constant matter of concern among researchers and common men.

Some days before some researcher told that herd immunity can protect from corona infection and let the people get infected with corona infection.Isolation and lockdown is barrier in spreading the infection and this will not let the herd immunity to develop.

According to some worker if 60 percent population become infected with corona virus rest 40 percent will become immune by herd immunity it self,but it's a double edges sword as if the infection is spread to 60 percent population then all the medical facility will become short and there will be severe shortage of ICU beds and ventilators and it will cause huge mortality also as there is no specific treatment or vaccine for corona virus at present.

So let's discuss the herd immunity here.

          Herd immunity and Corona virus

Herd immunity term was used first time in 1923.It was first recognised for measle in 1930 when number of new patient decreased in non immune but susceptible children after massive vaccination.

This is the method by which many disease have been eradicated in past like smallpox in 1977.
This kind of immunity works for infectious diseases only it means which is transmited from one person to another. It works for contagious disease only not for all kind of infection.

                    हिंदी में जानकारी के लिए वीडियो देखें

HOW HERD IMMUNITY DEVELOP

Herd immunity is of two type innate and acquired herd immunity.
Innate herd immunity develop as result of natural selection while acquired herd immunity develop when a large proportion of a population become immune to some particular infection by active vaccination or by infection then non immune person also become protected from that particular infection.This can be developed by active immunization or passive immunization

It works by breaking the chain of infection .

Herd immunity is specially helpful for those who can not become immune by them selve like immunosuppressive or immunodeficient individual.

High level of immunity in one age group can protect other age groups also by creating a barrier for transmission of infection,like pertussis vaccination in adult protect the very young infants from the same.

Similarly vaccination with PCV and rota virus vaccine decrease the infection in older age group who generaly don't get vaccinated for these.

But this kind of protection is not seen in influenza vaccine due to waning of immune system with age.

Harm of herd immunity

Here immunity induce evolution in viral genome and produce Noval strain of viruses.due to antigenic drift.It means when a sufficient mutation accumulate in viral genome it change the virus surface antigen. 

similarly when many strain of any virus are there in circulation then they may cause recombination of seprate viral genome and produce a noval strain which is not recognised by memory T cell it is called antigenic shift.

At this stage herd immunity fail in protection and there comes the need of universal vaccine which can protect all kind of serotype of particular virus.

Limitations of herd immunity

When free riders(those who are not vaccinated but protacted only by herd immunity only) increase then outbreak may occur for that infectious diseases.

 BASIC REPRODUCTION NUMBER(R°)

Basic reproduction number is  is expected number of new case directly generated by single case in a susceptible population.

This is not a constant value for any pathogen as it is affected by many factors

Like environment factor like wether and season. Agent factors like duration of infectivity, infectiousness of the organism and host factors like age groups, morbidity etc.

If the R° is more then one then infection will start spreading in a population.if R° is less then one there is very less chance of population spread.R predict the probability of major outbreak.If R is less then one P=0,and if R is more then 1 , then P is more then 0

Here are some  basic reproduction number of disease
SARS       2-5
COMMON COLD       2-3
COVID-19        1.4-3.9
INFLUENZA 1918 STRAIN     1.4-2.8
MERS      0.3 -0.8

HERD IMMUNITY THRESHOLD

This is the value of immune population needed to stop further infection in a given population.and it depends on the basic reproduction number.

If basic reproduction rate is high then HIT will also be high.it is calculated in complex equation in epidemiology.

For example if basic reproduction rate for any disease is 2 then HIT will be 50%

And if basic reproduction rate is 10 then HIT will be 90%.