What is herd immunity ?
The concept of herd immunity is typically described in the context of a vaccine. When enough people are vaccinated, a pathogen cannot spread easily through the population. If you are infected with measles but everyone you interact with has been vaccinated, transmission will be stopped in its tracks.
Herd immunity refers to preventing an infectious disease from spreading by immunising a certain percentage of the population. While the concept is most commonly used in the context of vaccination, herd community can also be achieved after enough people have become immune after being infected.
The premise is that if a certain percentage of the population is immune, members of that group can no longer infect another person. This breaks the chain of infection through the community (“herd”), and prevents it from reaching those who are the most vulnerable.
How can herd immunity be achieved?
Herd immunity can be achieved in two ways.
The first way is through mass vaccinations, which for COVID-19, is still under development.
The second way is through the infection which means that a person gets infected and after a while, they develop antibodies to fight the infection and thus become immune to it.
Since currently, the vaccine for COVID-19 is absent; countries around the globe like, the United Kingdom, the Netherlands, Sweden and Holland are experimenting with the second method.
There are a large number of people who are asymptomatic – who show no symptoms at all or have just mild symptoms like mild fever, mild cough. Most of these people will recover from the virus without getting hospitalized. This will contribute to increasing the herd immunity.
Once a lot of people develop the infection, about 80 per cent of them have mild symptoms but they overcome the virus and develop immunity. This happens as Immunoglobulin M (IgM) levels increase in their body initially and then Immunoglobulin E (IgE) levels.
IgM is mainly found in blood and is the first antibody that the body makes when it fights a new infection.
IgE is normally found in small amounts in the blood but the number may be higher when the body overreacts to allergens or is fighting an infection from a parasite. This immunity helps in preventing re-infections and when a large extent of the population develops this immunity then the risk of new infection or cases decrease.
What are the risks involved in building herd immunity through infections?
While it may prove to be effective in the long run, shooting for herd immunity right away would be a dangerous strategy especially because there is no vaccination, according to experts.
This is because a large number of people will become severely ill causing a sudden boom in sick people needing hospital or ICU (Intensive Care Unit) care, ventilators or oxygen support which will overwhelm the healthcare system of the country.
Effectiveness of herd immunity approach for a country will depend on the structure of the population of that country.
In India, the dominating population is of youth. Young people are generally healthier with a stronger immune system than the elderlies. They can fight with the infection and build immunity against it in a much faster way. This is true with any kinds of viral infection.
However, in Europe, much of the population is older because of which these countries there have experienced more severity and more fatality as far as COVID-19 is concerned. Since the immunity is low among most of the population, depending on herd-immunity through infection is not a wise step considering the gravity of the pandemic. Great Britain tried herd-immunity, it failed very badly.
WHO director-general Dr. Tedros Adhanom Ghebreyesus has also emphasized on not easing the lockdown restrictions as only a tiny proportion of the global population, maybe as few as 2 per cent or 3 per cent, appears to have antibodies against coronavirus.
The experts recommend that while the social distancing norms must remain enforced, the health authorities and policymakers should be cautious about herd immunity as there is no shortcut and the country should ideally try to achieve herd immunity through vaccination.
COVID-19 and herd immunity
There are several reasons why herd immunity isn’t the answer to stopping the spread of the new coronavirus:
- There isn’t yet a vaccine for SARS-CoV-2. Vaccinations are the safest way to practice herd immunity in a population.
- The research for antivirals and other medications to treat COVID-19 is ongoing.
- Scientists don’t know if you can contract SARS-CoV-2 and develop COVID-19 more than once.
- People who contract SARS-CoV-2 and develop COVID-19 can experience serious side effects. Severe cases can lead to death.
- Doctors don’t yet know exactly why some people who contract SARS-CoV-2 develop severe COVID-19, while others do not.
- Vulnerable members of society, such as older adults and people with some chronic health conditions, could get very sick if they’re exposed to this virus.
- Otherwise healthy and younger people may become very ill with COVID-19.
- Hospitals and healthcare systems may be overburdened if many people develop COVID-19 at the same time.
Herd immunity for COVID-19 in the future
Scientists are currently working on a vaccine for SARS-CoV-2. If we have a vaccine, we may be able to develop herd immunity against this virus in the future. This would mean getting the SARS-CoV-2 in specific doses and making sure the majority of the world’s population is vaccinated.
Almost all healthy adults, teens, and older children would need to be vaccinated to provide herd immunity for people who can’t get the vaccine or who are too ill to become naturally immune to it.
If you’re vaccinated and build immunity against SARS-CoV-2, you most likely wouldn’t contract the virus or transmit it.
Herd immunity isn’t the answer to stopping the spread of SARS-CoV-2, the new coronavirus that causes COVID-19. Once a vaccine is developed for this virus, establishing herd immunity is one way to help protect people in the community who are vulnerable or have low functioning immune systems.
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