Introduction
Herd immunity is a scientific phenomenon that occurs when a large portion of a certain population becomes immune to a disease through vaccination or previous infections (by building antibodies), reducing the likelihood of the disease spreading. This protects individuals who are not immune, such as those who cannot be vaccinated (e.g., due to medical reasons like allergies or compromised immune systems). When enough people become immune, the disease has fewer opportunities to spread, which can ultimately lead to its control or complete eradication, saving a population and specifically its vulnerable members from illness.
Vaccines play a critical role in establishing herd immunity. By immunizing a significant percentage of the population, vaccines reduce the overall spread of disease, protecting vulnerable groups such as children or elders, and eventually controlling outbreaks. The level of vaccination coverage needed to achieve herd immunity varies depending on the disease and its overall transmission rate.
A History of Herd Immunity
- Chicken Pox
According to Penn Medicine, Chicken pox is a viral infection that causes itchy blisters and rashes, as well as other viral symptoms. It is spread through airborne droplets in coughs or sneezes, as well as touching a contaminated surface. Chickenpox is much less severe in childhood than in adulthood, and contracting the virus just once guarantees immunity for life (by building antibodies).
Hence, some turned to “pox parties” before the introduction of the varicella chickenpox vaccine in 1995. These social gatherings would include parents deliberately exposing their children to other children with chickenpox. Their goal was to “get it over with” so that the children would develop immunity and there was less risk of dying from chickenpox in adulthood. This type of exposure to illness promoted increasing the number of immune individuals in a community, reducing the likelihood of future outbreaks, and protecting people within the population who had never contracted this illness.
- Measles
According to the World Health Organization, measles is a highly contagious and deadly disease. Often, it causes rashes, high fevers, coughs, and runny noses and spreads whenever someone coughs, sneezes, or even breathes. Measles primarily affects young children under the age of five and has been recognized since the 9th century. In the 10th century, a Persian physician named Muhammad ibn Zakariya al-Razi provided the first accurate description of the disease, differentiating it from smallpox, according to Patrick Berche, a celebrated French physician and PhD. Measles throughout history would continue to be studied, and eventually, the development of a vaccine came in 1963 by John Enders. Once the vaccine was widely distributed, fewer and fewer people contracted the illness, ultimately leading to herd immunity. In fact, health officials claim that herd immunity is 94%, or 94 out of 100 people need to be immune to stop the spread of measles. Moreover, herd immunity is easily maintained because it is a virus that remains relatively stable, which means there are generally no new strains of the virus. Nowadays, measles is such a rare illness to contract as most people have immunity or are vaccinated which helps to effectively eradicate the once fatal disease.
- Polio
Polio is another key example of vaccination causing herd immunity. Polio is a viral disease that invades the nervous system and causes paralysis. The virus is transmitted through contact with contaminated droplets. The late 19th and early 20th centuries saw frequent epidemics, as polio became the most feared disease in the world, with one outbreak killing over 3,000 people. The Global Polio Eradication Initiative was established by the World Health Assembly in 1988 with the hopes of mass immunization to polio through vaccination. The hope of the initiative was that if immunity could reach a certain level, called the “herd immunity threshold,” then the infection rate of polio should decrease dramatically, almost to zero. The goal was to eradicate the disease in 12 years, and by the year 2000, 99% of the incidence of polio had declined globally. By providing vaccinations to large portions of the population, the GPEI created herd immunity and effectively saved millions of lives.
Is Only Herd Immunity Enough?
Throughout history, herd immunity has led to entire communities being shielded from devastating illnesses, saving millions of people including vulnerable populations. But, during the COVID-19 pandemic, this idea sparked debate among scientists. They believed there were more effective ways to eradicate the disease. At the height of the pandemic, healthcare experts in Sweden advocated against herd immunity as the virus was rapidly mutating, and vaccines were not widely available. They also asserted that this method, involving allowing the disease to develop and spread in the hope that eventually the population will become immune, would overwhelm healthcare systems, prolonging the public health crisis. When compared to previous instances where herd immunity was used (such as smallpox or measles), COVID-19 was unique. This is because variants, such as Omicron or Delta, were proliferating at extreme rates, bypassing herd immunity. Hence, even those that had developed antibodies and become immune to one strain of this illness, could become reinfected, undermining the goal of herd immunity. Another argument claims that allowing this illness to pass naturally could exacerbate previously existing inequalities. Antibody tests done throughout communities in New York City showed higher rates of infection in low-income, Latino neighborhoods.
In conclusion, the discourse surrounding herd immunity during COVID-19 led to important discussions about the ethical implications of herd immunity. While herd immunity has been used many times in the past to successfully eliminate outbreaks, the unique characteristic of COVID-19 led many experts to reject the methods of herd immunity. They argue that vaccines remain the more efficacious solution to control the spread of COVID-19
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