Herd immunity is also known as community immunity or herd or group protection against some communicable infections. Some experts have suggested that this might be a good way to prevent the spread of coronavirus or COVID-19. Herd immunity is a condition acquired when most of a population becomes immune to an infectious disease, thus preventing the spread of the disease. Depending on how contagious the disease is, about 70% to 90% of a population needs immunity to attain herd immunity.

This can be achieved in two ways:

Vaccination of many people for the disease to achieve immunity

Many people contract the disease and after a period of time build an immune response to it. This is known as natural immunity.

Has herd immunity worked for other diseases in the past?

Our previous experience has shown that herd immunity was possible against diseases like mumps, measles, and polio due to the vaccination of most of the population. In the past, there has been an outbreak of diseases that are vaccine-preventable due to low herd immunity in communities that have a low rate of vaccine coverage.

For diseases without a vaccine, even if many adults have developed immunity due to prior infection, the disease can still affect those with a weak immune system or children who are vulnerable. Other viral infections such as the flu, mutate frequently, so antibodies from a prior infection provide immunity only for a short period of time, usually lasting one season.

How does herd immunity work?

When most of a population becomes immune to a disease, the spread of that disease is prevented or slowed down. This occurs because the chain of transmission from one person to the next is broken when most people are immune. This protects the vulnerable population or those who are not vaccinated which includes children, babies, elderly, and those with a weakened immune system.

Herd immunity works for some diseases. Few countries have achieved partial herd immunity for diseases such as the swine flu caused by the H1N1 virus by vaccinations and natural immunity. Herd immunity can help to reduce the spread of diseases or pandemics within a region or country. However, it does not guarantee protection for every individual even though it can help reduce the number of people getting affected.

Herd immunity does not work for every disease. For example, diseases like tetanus that do not spread from one person to another can only be prevented in an individual by vaccination.

Herd immunity is not a good option for healthy people when compared to vaccination. You can help build immunity to certain diseases in a community by getting timely vaccinations.

Natural immunity

Natural immunity is attained by contracting the disease in question. Acquiring an infection triggers your immune system and leads to the production of antibodies that target the specific pathogen (the causative germ). If you contract the disease again, the antibodies that dealt with the pathogen attack it before it can multiply within your body. For example, if you have had chickenpox in your lifetime, you are unlikely to get it again even if you come in contact with an infected person.

Natural immunity does not work as well as vaccinations because of multiple reasons:

Contracting the disease can manifest in a life-threatening way depending upon their immune status

Most people in a population would have to contract the disease at least once for herd immunity.

You may not be aware of your immune status.

COVID-19 and herd immunity

Currently, the only ways to prevent the spread of COVID-19 caused by SARS-CoV-2 are by social distancing and frequent hand washing. Herd immunity may not be successful in preventing the spread of the new coronavirus. This is due to several reasons:

There is no vaccine for COVID-19 yet. Vaccinations are the safest way to acquire herd immunity.

Successful antiviral specific for COVID-19 are still under research.

Scientists and researchers are uncertain if you can contract SARS-CoV-2 and develop COVID-19 more than once even though we developed antibodies

People who are infected with SARS-CoV-2 can develop life-threatening symptoms which can even lead to death. This is still higher among the vulnerable members of the society such as the elderly, or those with underlying comorbid health conditions. Otherwise healthy and younger people may also become very ill on exposure to the virus.

If too many people test COVID-19 positive simultaneously, healthcare systems and hospitals may be overburdened and cannot handle the high number of cases. This can cause serious collateral damage on the existing health care system.

Doctors are still trying to understand why some people develop severe complications while others don’t.

What should we expect in the months ahead?

Herd immunity is not the answer to preventing the spread of COVID-19.

Scientists are working on a vaccine for SARS-CoV-2. With a successful vaccine, we may be able to achieve herd immunity in the future. This would work only when the majority of the world is vaccinated. Almost all children, healthy adults, and teens would have to be vaccinated to prevent herd immunity for people who cannot be vaccinated or are too ill to be naturally immune.

If you are vaccinated and you build immunity against SARS-CoV-2 and are unlikely to contract or transmit the infection.

Establishing herd immunity during this pandemic is only possible with the help of an effective vaccine unless we are willing for the majority of our population to get infected.

Once the vaccine is developed, we can hope to protect the weaker and vulnerable members of society. Physical distancing measures need to continue to be in place until a vaccine is available. Life is not likely to return to normal until a successful vaccine is developed and widely distributed.