Herd Immunity is a form of immunity
that occurs when a significant portion of a population is vaccinated and in
turn provides a measure of protection for the individuals who have not
developed immunity. When this critical percentage of the population is already
protected through vaccination against a virus or bacteria, it makes it
difficult for a disease to spread because there are few vulnerable individuals
left to infect.
The term herd immunity was first
coined in 1923, recognized as a naturally occurring phenomenon in the 1930s
when it was observed that after a significant percentage of children had become
immune to measles, the number of new infections temporarily decreased,
including among vulnerable children. Mass vaccination in order to
actuate herd immunity has since become common and proved successful in
preventing the spread of many contagious diseases. During the smallpox
eradication campaign in the 1960s and 1970s, the practice of ring
vaccination, of which herd immunity is integral to, began as a way to
immunize every person in a "ring" around an infected individual to
prevent outbreaks from spreading.
This is highly effective in
stopping the spread of a disease in a community. It is particularly crucial for
protecting people who cannot be vaccinated. These include infants who are too
young to be vaccinated, immunocompromised people, and those whose medical
condition doesn’t allow them to receive vaccination (such as cancer patients).
However the percentage of a
population which must be immunised in order to achieve herd immunity against a
specific disease varies for each disease. Once a certain threshold has been
reached, herd immunity gradually starts eliminating a disease from a population.
This elimination, when achieved worldwide, results in the permanent reduction
in the number of infections to zero, called eradication. Till date, two
diseases have been eradicated using vaccination and herd immunity: smallpox
and rinderpest.
However, when immunisation rates
decline, it becomes difficult to retain herd immunity, leading to an increase
in the number of new cases.
Actually, for b.pertussis and measles this picture is wrong, because either immunized by vaccines or not immunized by the vaccines can spread the diseses. But the biggest risk is, when immunized are not aware that they are infected/are source of infection, as they are not signalizing it by the disease symptoms.. So it creates something like false impression that vaccinated people are the break of spreading. And this is not true, that those not vaccinated don't have immunity. Actually if they were sick, their immunity is stronger than those vaccinated. Even if not having the disease - there are people who are immune just because their body is strong. So - false assumptions makes false understanding of topic and provides false conclusions.
ReplyDeleteAnd herd immunity .. is about real immunity that can be related to vaccination, but is not the only source of immunity and shouldn't be treated in this way.