Author: Anshuman Rawat

You probably heard the term ‘herd immunity’ (also called community immunity and herd or group protection) in relation to the coronavirus disease outbreak when some governments, including that of UK Prime Minister Boris Johnson, (are said to have) considered allowing herd immunity to develop on its own, without a vaccine, by letting the virus spread through their populations.

The argument was that though it might lead to a trail of deaths, the coronavirus would have left millions of recovered people with antibodies to fight it.

The chief science adviser to the UK government, Sir Patrick Vallance, said the country needed to “build up some kind of herd immunity — by having potentially 60% of the population (40 million people) contract COVID-19, as one of the “key things we need to do” — so more people are immune to this disease and we reduce the transmission”.

Later, however, Matt Hancock, the UK Secretary of State for Health, clarified that “creating so-called ‘herd immunity’ in the UK against coronavirus is not part of the Government’s plan for tackling the killer illness”.

Herd immunity happens when so many people in a community become immune to an infectious disease that it stops the disease from spreading.

The underlying scientific/medical argument is that

…individuals could gain immunity to the new coronavirus if they develop antibodies; that can happen through vaccination, or after they get infected and recover…

So, if enough people become immune, that can confer “herd immunity” to an entire population.

This protects even people who aren’t immune because so many others are immune that they prevent the virus from spreading within a community. Herd immunity would effectively end the coronavirus pandemic. Something like this:

It might not naturally occur to us that those who are infected with germs (e.g., viruses, bacteria) do not have the ability to infect infinite numbers of people. Individuals can remain contagious only for a limited time — before their own immune system clears the germ and they become non-contagious.

Equally, different germs require different doses of pathogen* to be transmitted in order to successfully infect another individual, and those that require higher doses may also require more prolonged contact to transmit infection.

[* A pathogen, broadly speaking, is anything that can produce disease. It can also be referred to as an infectious agent, or simply a germ.]

There has been past evidence for the emergence of herd immunity in other recent outbreaks.

In 2015, Zika virus, a mosquito-borne illness caused an epidemic panic. Two years later, in 2017, there was no longer nearly so much to worry about. A Brazilian study found by checking blood samples that 63% of the population in the northeastern beach city of Salvador had already had exposure to Zika; the researchers speculated that herd immunity had broken that outbreak.

In a radically different environ, Norway is said to have successfully developed at least partial herd immunity to the H1N1 virus (swine flu) through vaccinations and natural immunity. Similarly, in Norway, influenza was projected to cause fewer deaths in 2010 and 2011 because more of the population was immune to it.

But the thing about such data is that there is not just as much of it as one might want to decisively conclude in one direction or the other.

For a population to achieve herd immunity, a certain proportion has to be immune. That proportion depends on how infectious a virus is, a measure called R0 (pronounce ‘r-naught’) — the average number of people that a victim passes the virus on to.

The more contagious it is, or the higher the ‘Ro’ is, the more people need to be immune for the infection rate to start falling.

For some diseases, herd immunity can go into effect with as little as 40 per cent of the people in a population becoming immune to the disease, such as through vaccination. But generally, a much higher percentage of a population must be immune to the disease to stop its spread.

For example, it has been found that 19 out of every 20 people must have the measles vaccination for herd immunity to go into effect and stop the disease. This means that if a child gets measles, everyone else in the population around them will most likely have been vaccinated, already have formed antibodies, and be immune to the disease to prevent it from spreading further. If that is not the case, and if there are more unvaccinated people around the child with measles, the disease could spread more easily because there is no herd immunity.

And therein lies the problem with the option.

There is no vaccine currently available for COVID-19. We never know when it might arrive. So, the only hope currently is to develop herd immunity via contracting the Coronavirus.

Supporters of the method argue that about 493,000 people have recovered from the coronavirus already, and it’s likely they are now resistant.

The counter is: What is the degree of immunity?

The world has no idea how long the affected (and recovered) will stay immune. (With some coronaviruses, as well as with ordinary flu, the immunity lasts less than a year.) Also, even if they stay immune for long (like, until the vaccine arrives), the world has no idea how long it would take to reach herd immunity.

It is also unclear how much protection antibodies confer on people who have recovered from COVID-19.

Some early research suggests that not all recovered patients develop coronavirus-neutralizing antibodies to the same degree. According to a report (that has not yet been peer-reviewed) from Chinese scientists, about 10 of 175 participants studied did not develop neutralizing proteins. This suggests they could have a higher risk of reinfection! 

That report too does not give enough knowledge. Nothing so far has.

So, perhaps (since we are not medical researchers or doctors), herd immunity isn’t the answer to stopping the spread of COVID-19.

Once a vaccine is developed for this virus, establishing herd immunity could be one way in the future to help protect people in the community who are vulnerable or have low-functioning immune systems.