Herd immunity will not work

Bearing in mind the “herd immunity threshold” and factoring in the quantum of contagiousness of a disease

Shariq Jamal Khan May 20, 2020
A Reuters file image.

Covid-19 is still in our midst. We are not even sure what it is doing to our people. We possess scant information regarding the pathogenic trajectory it will follow in the future. Worryingly, we are also unsure of its collective prognosis. A self-created myth that things are re-entering the realm of normality is making us naïvely fearless, impetuous and complacent. Many Pakistanis believe they are immune to the disease and cite a host of ridiculous reasons for that. Myriad ethno-pharmacological concoctions of herbal remedies, home-made “curative” hodge-podges and incantations are being confidently proffered as the treatment for Covid-19. Herd immunity is another “cure” that is being bandied about gleefully. Many bright and educated people are also presenting it as a viable option to curb the virus’ spread. This is mere hogwash.

What is herd immunity? When a sufficiently high percentage of people in a population become immune to an infectious disease, that immunity can create a natural protection shielding those not immune to the ailment. The percentage of people that need immunity to break the natural transmission chain of an infectious disease is called the “herd immunity threshold”. According to experts at the Johns Hopkins Bloomberg Public School of Health, if 80% population is immune to a virus, four out of five who interact with an infectee will not be affected. The net result is that the infection would not spread further.

Bearing in mind the “herd immunity threshold” and factoring in the quantum of contagiousness of a disease, usually 70-90% of a population must become immune before herd immunity could work. Three points need to be underscored here.

Firstly, it must be unequivocally asserted that herd immunity will not work in case of Covid-19 in Pakistan as it is epidemiologically untenable and scientifically unattainable. The arithmetic involved distressingly reflects that. Data from studies has demonstrated that Covid-19 tends to infect a relatively small number of people in a population, which means that a low proportion of people have antibodies in their systems. Consequently, the much-heralded herd immunity cannot be achieved. It would be a diabolical mistake to bank on herd immunity to stop Covid-19 from spreading in Pakistan. Though, by no means accurate, as per early estimates of the infectiousness of Covid-19, about 70% of the population must be immune to produce herd immunity. This means that 148 million Pakistanis must first become immune to achieve herd immunity. This could be an unmitigated disaster.

Secondly, herd immunity is usually created artificially with the help of focused vaccination drives. Based on cautious calculations, a portion of the population is immunised in order to reach the herd immunity threshold. Once done, herd immunity is created which can then protect the vulnerable population. Vaccination works when substances called antigens are plucked from the pathogen in question and introduced into the body to elicit an immune response. Vaccines exploit the natural activity of the immune system by strengthening it to combat the new invading antigens by producing antibodies or immunoglobulins. If an attempt is made to produce herd immunity without a vaccine, children, pregnant women, older persons and people with compromised immune systems will be infected. This will also leave our health system in tatters.

Thirdly, viruses can mutate over time, thereby rendering the antibodies from an earlier infection redundant. WHO has stated that it appears that immunity from Covid-19 could only last for a year. In that case, herd immunity will also become redundant.

It would, therefore, be prudent to wait for a vaccine to be developed; till then follow the prescribed set of rules and SOPs to prevent Covid-19 from spreading.

Published in The Express Tribune, May 20th, 2020.

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