INTERVIEW | Herd immunity is natural journey of any epidemic, says epidemiologist

Emphasising why herd immunity is important, Dr Muliyil says that hiding will always make a person susceptible.

Published: 13th April 2020 04:23 AM 

Dr Jayaprakash Muliyil

By Sumi Sukanya dutta

Express News Service

One of India’s best-known epidemiologist and former principal of Christian Medical College, Vellore, Dr Jayaprakash Muliyil tells Sumi Sukanya Dutta that the country should prepare for a continued battle with Covid-19. Emphasising why herd immunity is important, Dr Muliyil says that hiding will always make a person susceptible and if the elderly are protected and transmission is allowed in the younger population, in a staggered manner, it can work.

We are now into the third week of the nationwide lockdown, how effective has it been in terms of containment of COVID-19 outbreak?

Lockdown serves the purpose of reducing transmission, which might occur at an exponential rate. It is difficult to make people participate in such an exercise because a majority of the Indians won’t even understand what a virus is. In one sense, it has created awareness among the people and I hope the population practices social distancing measures in the weeks to come. Of course, not everybody would have learnt but a good proportion of people now know how to reduce the chance of getting infected and for that alone the lockdown has made a difference. Two main things that have been achieved are—slowing down transmission and creating alertness.

The number of fresh coronavirus cases that we are seeing every day has been considerably high—around 800-900 cases on some days despite the lockdown. Why is that?

I wonder if anyone thought we will get rid of the virus completely through the lockdown. The idea was to slow down transmission and whether it was a success or not subsequent analysis will show. The chances are that there was a small dent in the rate of transmission. Also, it gave us time to prepare ourselves for the grim situation of dealing with a high number of people approaching hospitals. The reality is we should prepare ourselves for a continued battle.

How do you see India’s effort in containing the outbreak? Could we have done anything differently in the beginning — for instance, essentially quarantining all international travellers coming to the country since early March maybe?

This is a new disease and all the information we have accrued is over the last four months but it’s clear that a country like India could not have prevented the virus from establishing the foothold. Now, small countries like New Zealand have managed to contain it and that’s because those societies are much more organised and people follow directions. We, on the other hand, are a huge country with diversity and education and income levels that vary vastly. We could not have stopped travels overnight. We eventually did but infectivity and transmission of the disease is something that made the virus extremely viable. It’s also a helpless situation even for the governments. Let’s not get into blame games. We have to move away from the institutional quarantine of every positive person. Those with mild symptoms can be home quarantined. at home.

You have spoken about natural herd immunity to overcome the epidemic? What does that mean?

Whenever a new virus emerges they have an easy way around because everyone is susceptible and the pathogens travel from person to person at will. You can try and keep yourself protected but for how long?

Somewhere along the line, it will catch you. Viruses—like measles, Influenza, induce an immune response and that can kill the viruses completely, that’s the blessing we have. After someone’s body has killed the virus the body forever remembers that pathogen and you become immune to it for the rest of your life. I believe, SARS CoV 2 behaves like many other viruses and triggers an immunological response in individuals. Those who recover after battling it will become protected from it. After a sizeable proportion of the population becomes immune to a virus that’s called herd immunity and a virus finds it hard to thrive because it’s difficult to find a host that’s vulnerable. In the case of Influenza—the population that required herd immunity to stop the epidemic was 40 per cent. Once we reached 40 per cent in a locality—the epidemic seized. It was like magic. So a locality and then a country has to reach a certain level of herd immunity. For COVID-19, we do not know what that level is but with analyzing the data as it emerges—we will know that. People sometimes say it’s not a good strategy but it’s not a strategy—it’s the natural journey of an epidemic whether you like it or not. The only thing is that during the process many people can die and the elderly above 60 will be the most susceptible. The rate of death among younger people is very low but even if one young person per 1,000 dies due to the disease, the absolute number could be significant because we have a huge population. The infection, therefore, must be slowed down.

Are you saying that the government should allow slow progression of the disease in order to achieve herd immunity?

Remember, if you keep hiding you always remain susceptible. The virus causes just mild symptoms in the young and in people above the age of 60 years, the mortality is high. In India, nearly 12 % of the population is over 55, so a large chunk of the population is not vulnerable in terms of fatality rate. In my view, if the elderly are protected and transmission is allowed in the younger population, in a staggered manner, it can work. For instance, big gatherings should be avoided and social distancing should be maintained. But societies and industries should be allowed to function at a slower rate. Young people who catch the infection will mostly keep recovering. But that doesn’t mean it won’t come back again. It might come back in a year or so but by then, we may have a vaccine to protect all.

You are suggesting protecting the elderly but can that be possible in a country like ours?

At the family level, the elderly can be kept in a room and though WHO suggests a distance of one meter, I will say follow the rule of maintaining at least two meter’s distance. Remember, maintaining a physical distance, for the time being, is important.

There is a chance that they might still get infected but it will reduce the spread. Having said that I do understand that in some areas like urban slums, it will not be easy.