Herd immunity is a situation where a majority of the population in an area is immune to a particular virus, bacteria or other pathogen.
It leaves behind a trail of people who develop immunity to that virus. Such people are unlikely to fall ill to the same virus again. When enough number of people in a geographical area have developed such immunity, the virus loses its transmissibility.
This is herd immunity. In this situation those who did not get the disease are supposed to be less vulnerable to that particular virus.
There are arguments Covid-19 will stop being a threat when India or the world reaches that stage of herd immunity.
However, it is not yet certain as to how many people should get infected for a society to develop herd immunity to Covid-19
Immunity is the key. To boost immunity, we take Medicines, Fruits & Vegetables, Vitamins and Minerals which on their own don’t kill viruses. It is our immune system that fires antibodies at the intruding viruses and other pathogens to neutralise them.
Medicines just aid the process of antibody production. Antibodies are shields that we have against a virus. But there is no medicine against coronavirus infection.
Vaccines are similar. They raise a standing army of antibodies in the body for a targeted disease or pathogen. But there is no vaccine against Covid-19 yet.
These two basic deficiencies have bolstered the conversation around herd immunity.
But can herd immunity really protect us against Covid-19?
Is this herd immunity actually achievable?
There is no agreed formula, but generally speaking, if 60 to 90 per cent of the population of a place is immune to a virus, herd immunity is attained. Herd immunity has been achieved for diseases such as polio, measles, mumps, and even chickenpox, but mostly through painstaking immunisation programmes in India and across the world.
The problem with viruses is that most of them mutate fast. This is the reason why a very effective vaccine against common flu — caused by the influenza virus — has not been made.
Current vaccines need to be administered every year or so to give protection against common flu. Large number of people continue to get common flu every year.
There is a second issue with herd immunity that emerges from recent experience in the US and also Europe. In the past few years, the US has seen serious outbreaks of measles.
The US has vaccine coverage for measles at over 90 per cent. Those not in the coverage are largely a result of the anti-vax campaign. The campaigners argue that vaccines are impacting natural immunity of humans. They get support from the champions of herd immunity who say that if herd protection has been achieved everybody does not need to get vaccine administered.
There is another problem with herd immunity: the problem of herd. A person’s herd changes with movement, relocation, migration or even tourist travel. Even a new circle of friends is capable of breaching herd immunity.
There is one more issue with advocating herd immunity for Covid-19. The case fatality rate of Covid-19 is higher than many other infectious diseases, most common of all being the flu. Covid-19 is essentially an oxygen-starving illness.
This is why Covid-19 aggravates most co-morbid conditions. So, while herd immunity may be a reasonable approach for diseases such as the flu or even measles, it can be an extremely risky proposition for Covid-19.
Furthermore, even with about 3 lakh coronavirus cases, the Covid caseload is only a fraction of the over 135 crore population of India.
On a global scale, the 72 lakh coronavirus cases are an equally small percentage of over the 750 crore people of the world to think of any realistic herd immunity as protection unless a super vaccine is developed and administered to enough people.