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Covid-19 and herd immunity: Everything you need to know

According to Dr Rajeev Boudhankar, internal medicine (MD) and CEO-Bhatia Hospital, “in India, given the present status of the pace of vaccination and availability of vaccines, it is still a long way to develop herd immunity”

Even as India’s effective reproduction number (R) for Covid, an indicator of how fast the viral infection is spreading, has hit a record low of 0.78 according to reports, many experts say that India may be far from achieving herd immunity or indirect protection or population immunity against the disease — a situation when most of the population is immune to the virus. To understand more, we reached out to health experts.

Here is what they had to say:

How is herd immunity achieved?

The term herd immunity refers to community, population, or mass-level immunity against a particular infectious disease. Herd immunity with safe and effective vaccines makes diseases rarer and saves lives.

We can get herd immunity in two ways. One is naturally, when everyone tends to develop antibodies against the disease. That is when most of the population gets infected or sick by the virus and thus acquires natural immunity by producing antibodies against that pathogen. Another way is through mass vaccination of people which provides artificial immunity, explained Dr HK Mahajan, anaesthesiologist, Indian Spinal Injuries Centre, Vasant Kunj.

“There are T memory cells in our bodies that can recognise the virus and protect against that by producing antibodies in future. The vaccine produces artificial immunity so that when an infection occurs, our body can recognise the virus and start producing antibodies. In case of coronavirus, however, many mutations and new variants are happening frequently and causing agonising health problems and complications,” he said.

Herd immunity is usually achieved for viruses that do not mutate and are stable. “Since we do not have deep insights into the Covid-19 virus right now we can only hope that there will be herd immunity built into the system when around 50-60 per cent of people are infected and recovered,” said Dr Shuchin Bajaj, founder and director, Ujala Cygnus Group of Hospitals.

Stating that in Delhi, 24 per cent of people infected and recovered have developed immunity and antibodies, Dr Bajaj mentioned that it is being hoped that in “another one or two months”, herd immunity may develop. “But if the antibodies disappear or the virus mutates, then this herd immunity will not be there any longer. This myth that herd immunity will always be present may not work here, as we see it in cases of influenza virus to which people fall prey every year and catch a common cold, because the virus mutates very quickly and presents as a new version every time,” he said.

However, research is still ongoing into how strong that protection is and how long natural immunity lasts. World Health Organization (WHO) states on its website that it is also looking into whether the strength and length of immune response depend on the type of infection a person has: without symptoms (‘asymptomatic’), mild or severe. Even people without symptoms seem to develop an immune response.

WHO supports herd immunity through vaccination, not by allowing disease to spread through any segment of the population, as this would result in “unnecessary cases and deaths”.

According to Dr Nanditha C N Gowda, consultant- General Medicine, Apollo TeleHealth, “Vaccinated people are protected from getting the disease in question and passing on the pathogen, breaking any chains of transmission”. “The SARS-CoV-2 virus is a highly transmissible virus. If you allow this to happen naturally, it will take a long time, of course, but more importantly, it’s going to do a lot of collateral damage. This is an important area of research and will likely vary according to the community, the vaccine, the populations prioritised for vaccination, and other factors,” noted Dr Gowda.

According to Dr Mahajan, in our country at least “80 per cent of the population needs to be vaccinated in order to achieve herd immunity”. “We have to observe which vaccines remain more effective — for example, Pfizer or Moderna vaccines in the US are said to be 90 to 95 per cent effective. In India, we are getting Covishield, Covaxin, and Sputnik which are said to be effective on mutants and variants. But with the new Delta plus variant and an anticipated third wave in future we need to find out ways and means to achieve herd immunity by focusing on mass vaccination,” he said.

As per Dr Rajeev Boudhankar, internal medicine (MD) and CEO-Bhatia Hospital, “in India, given the present status of the pace of vaccination and availability of vaccines, it is still a long way to develop herd immunity”.

What are the parameters?

We have to achieve immunity through vaccination, stated Dr Mahajan. “As we all are foreseeing that the third wave will be dangerous for children, we need to protect the parents also. The Uttar Pradesh Government, for example, is focusing on vaccinating parents so that children may get protection. This means that we have to develop herd immunity indirectly too for the health of our children and elderly. This battle can be won by public sensitisation and community vaccination only,” he said.

With just about four per cent of the population vaccinated, it is expected that the “third wave is no more a guesswork but a definite event expected”, said Dr Boudhankar. “Moreover, the vaccination program has still not reached our rural population on a large scale, where 70 per cent of our people live. This makes the situation grimmer not only for the development of herd immunity but also for the third wave,” he added.

Until herd immunity is achieved, what can help?

Till that time, we need to observe Covid-appropriate behaviour. Use of face masks, social distancing, and hand hygiene is of utmost importance. “And then on the side, be able to detect rapidly those who are infected in the community, making sure that enough testing is available so that you’re able to detect and diagnose people, be able to isolate them, then test their contacts and quarantine them. These are the measures that have been shown to be successful. Only through vaccination, healthcare availability and strict regulations, we will be able to achieve the required goal,” said Dr Gowda.


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