Hyderabad: Among the many strategies to combat the highly contagious novel strain of coronavirus (SARS-CoV2), the concept of ‘herd immunity’ has come up frequently in the last few months. It suggests that a majority in the population can contract the virus or allow the virus to run its course and then wait for the infected to develop antibodies before becoming immune to the ailment.
So far, the herd immunity concept has worked in eradicating diseases like polio, measles, rubella and smallpox. Well-developed vaccines and their administration to a percentage of the general population, including children, have been successful in developing herd immunity among the community to such traditional diseases.
In theory, herd immunity may sound quite appealing, but as the United Kingdom recently found out, such initiatives come with challenges and risks. The country initially decided to work towards ‘herd immunity’ thinking that if most of its population gains immunity by getting infected, then the transmission of the ailment could be checked. However, the unstoppable nature of SARS-CoV2 and immense pressure on healthcare systems forced the UK
government to take a ‘U’ turn and adopt social distancing strategy to combat the coronavirus.
Even in India, the herd immunity theory is advocated through its national immunisation programmes by administering vaccines for polio, measles, mumps and rubella. The idea is that if most of the population i.e. children are vaccinated, then a small percentage of the remaining can go unvaccinated because there will be no transmission of the disease.
Will herd immunity work for SARS-CoV2?
Top experts, including noted epidemiologist and Professor, Head, Life Course Epidemiology, Public Health Foundation of India (PHFI), Bengaluru, Dr Giridhara R Babu and Bhopal-based public health specialist and bio-ethics expert Dr Anant Bhan point out that there are many challenges the country has to face if it takes the herd immunity route.
The first challenge is the absence of an efficient vaccine for SARS-CoV2, which is at least 12 months to 18 months away. The second is the difficulties that India, with limited healthcare infrastructure, including critical care and manpower, will face if a sizeable population is allowed to get infected with the coronavirus.
Currently, there is also no clear picture of how long the immunity among recovered Covid-19 patients will last? Will the immunity last for six months, one year or two years? What happens if recovered persons lose immunity within a year? Will they have to be re-infected again?
In the absence of concrete answers to such challenges, senior health specialists pointed out that the lockdown and subsequent measures being adopted to test and isolate the positive cases were the best options available for a country like India.
‘A risky affair’
There are several challenges that governments and public health professionals need to address while pursuing herd immunity to combat outbreaks like Covid-19.
The first route to develop herd immunity is through vaccines. However, until an effective vaccine is available, we can’t even think about the concept.
At this moment, such a vaccine, in the best case scenario, is at least 12 to 18 months away. A lot will also depend on which country manufactures the vaccine and who gets access to it first. In case an ideal vaccine is available, then by immunising a percentage of the population, you reduce the chances of transmission. However, information on what percentage of the population must be immunised for coronavirus is not yet known.
The second option of herd immunity is to allow the virus to infect a sizeable population in a community in the hope that they develop immunity. Such a concept was adopted in the UK while handling the coronavirus outbreak. We should accept the fact that by adopting this approach, a sizeable number of vulnerable populations in the community like people with co-morbidities and the elderly will fall sick, resulting in fatalities. When you allow the virus to take its course, then governments must have adequate infrastructure and medical facilities to take care of such a vulnerable population. So both the routes of achieving herd immunity are challenging and governments must be careful about them.
— Dr Anant Bhan, Public health specialist and bio-ethics expert
‘Robust health infra prerequisite’
If countries adopt the strategy to allow pathogens like virus to run their course for developing herd immunity in a population, then they must also have in place appropriate healthcare systems that can respond to the infected persons. You should have enough number of doctors, ventilators and healthcare workers out there to meet the surge in cases. So, what will you do when you don’t have such kind of infrastructure to back you up? That’s the reason why many countries like India have adopted the strategy of lockdown. Some countries like Singapore initially applied the containment but later changed the course of their response by embracing the concept of lockdowns.
It is very difficult to accept a model where we want many people in a community to get infected with a virus. Based on the present-day epidemiology of Covid-19 across the world, nearly 15 per cent of the positive cases need hospitalisation while anywhere between 3 per cent and 5 per cent require intensive care like ventilator support. Can India with a population of 1.3 billion provide such kind of healthcare support to so many people who need critical care? Is that even possible to do so?
— Dr Giridhara R Babu (epidemiologist and Professor, Head, Life Course Epidemiology, Public Health Foundation of India, Bengaluru)
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