The fourth sero survey conducted across India found that on an average 67.6% of the population has been infected. Also, over 25% of people have been vaccinated with one dose. It is Erroneous to conclude we have attained herd immunity,’ says Dr. Srinath Reddy
What is herd immunity?
When most of a population is immune to an infectious disease, this provides indirect protection—or population immunity (also called herd immunity or herd protection)—to those who are not immune to the disease.
For example, if 80% of a population is immune to a virus, four out of every five people who encounter someone with the disease won’t get sick (and won’t spread the disease any further). In this way, the spread of infectious diseases is kept under control.
Depending how contagious an infection is, usually 50% to 90% of a population needs immunity before infection rates start to decline. But this percentage isn’t a “magic threshold” that we need to cross—especially for a novel virus. Both viral evolution and changes in how people interact with each other can bring this number up or down.
Below any “herd immunity threshold,” immunity in the population (for example, from vaccination) can still have a positive effect. And above the threshold, infections can still occur. The higher the level of immunity, the larger the benefit. This is why it is important to get as many people as possible vaccinated.
- Herd immunity happens when so many people in a community become immune to an infectious disease that it stops the disease from spreading.
This can happen in two ways:
Many people contract the disease and in time build up an immune response to it (natural immunity). Many people are vaccinated against the disease to achieve immunity.
When a large percentage of the population becomes immune to a disease, the spread of that disease slows down or stops.Many viral and bacterial infections spread from person to person. This chain is broken when most people don’t get or transmit the infection.
This helps protect people who aren’t vaccinated or who have low functioning immune systems and may develop an infection more easily.