Natural Herd Immunity Vs Herd Immunity Via Vaccine
The year 2020 will perhaps remain the strangest for many decades to come. A new virus jumps from bats to humans and starts spreading in Wuhan. From there it quickly spreads to other parts of the world. Humankind faces a pandemic and a state of emergency is implemented throughout the world.
With the start of the Covid-19 infection, people argued about the importance of herd immunity. Opposers of lockdowns used this idea to strengthen their point. It is true that herd immunity is important to develop because it can protect the population from infection. However, what many people do not understand is that in the case of SARS CoV-2, the burden of developing herd immunity is even heavier than imposing lockdowns.
Our body is designed to take care of itself. Food, reproduction, and defense are its main survival strategies. Our natural defense is maintained by the immune system. The immune system is composed of many components, which include different types of cells. These cells produce chemicals or antibodies and protect our bodies against “invaders”. When a person in a community gets exposed to any virus, the body starts to make antibodies. These antibodies defend the body against the attack that has entered it and they continue to do so in the future in case of another exposure.
Gradually, a whole community can develop immunity against the virus in this way. This is called natural herd immunity. In order to remain protected from the virus, a proportion of the population must be exposed to the virus. This threshold depends on the transmission rate of the virus. If a virus is fast spreading then the threshold will be higher. Measles is a highly contagious infection. More than 94% of a community must be immune to interrupt the spread of the measles virus. While achieving herd immunity we cannot rule out the danger of the disease.
In the case of SARS CoV-2, 60-70 percent of the population should be exposed to the virus in order to acquire herd immunity threshold to stop its spread. Another important factor is the method by which a virus transmits in a population. Some countries may have a greater spread than others, a greater number of immune-compromised people, a younger generation, and different genetic tendencies against the disease.
For Pakistan, achieving the threshold of 70 percent immunity in the population would entail the following. The estimated population of Pakistan is over 212 million in 2021. That makes its 70 percent to be about 148 million. To break the spread of SARS CoV-2 infections, 148 million Pakistanis should be exposed to the virus. But we have not considered asymptomatic infections, those people who do not show signs of infection and remain out of sight yet through them the virus keeps spreading. If we consider them too, our community threshold may increase to 90 percent which is around 191 million. Up till now, Pakistan has more than fifty-three thousand cases, with a 2 percent death rate, and more than forty-eight thousand recovered. This number has put our whole healthcare system under immense pressure. We have seen our healthcare providers dying, lack of infrastructure, unavailability of oxygen, overcrowded emergency wards, and shortage of professionals. Can we tolerate more patients if, out of exposed 148 million people, a few million developed the disease? Even if we have the system to handle this number, can we handle the emotional stress of seeing our beloveds in hospitals, or in graves? So the idea of depending solely on naturally acquired herd immunity fails for SARS CoV-2.
Thankfully, what we could not even dream of until very recently – the development of a vaccine in less than one year – has become possible due to scientists’ tireless work. The scientists are monitoring the situation keenly and efficiently so that time is not wasted on paperwork. This has its downside too; we have to monitor the data from clinical-trial phases for years. But given the gravity of the situation, scientists are collaborating more and more to make up for this shortcoming.
More than 60 million doses of vaccines have already been administered so far, but this is only the start of a very long work. What we know is that we need vaccination quickly to help develop herd immunity. In this way, the susceptible population will be protected. Till we can get a significant portion of our community vaccinated, we need to keep following the SOPs. Therefore, please keep observing a six feet distance from each other, avoid going to crowded places, wash hands, and always keep your face masks on.
Dr. Zareen Fatima has served as Assistant Professor at Department of Biological Sciences, International Islamic University Islamabad. She works on studying how virus evolves during epidemics in a region. In her free time she writes while enjoying a hot cup of tea. You can reach her at [email protected]