Buzz
In 1923, bacteriologists W.W.C. Topley and G.S. Wilson from the University of Manchester first introduced the term herd immunity in their research on how bacterial infections spread through a group of mice, some of which had been vaccinated [PDF]. Although they highlighted the need for further studies, their foundational idea was that a population could potentially gain protection from a disease if enough individuals were immune.
For instance, if a sick individual encounters five people, and four of them are immune to the disease, the infection could only affect the one vulnerable person. The other four would stay healthy, and they wouldn’t pass the disease to anyone else. This helps contain isolated cases and reduces the threat of a highly contagious disease to the larger community.
Almost 100 years after Topley and Wilson’s work, herd immunity has been observed multiple times in practice. As the Association for Professionals in Infection Control and Epidemiology explains, it often happens when the majority of a population is vaccinated against a specific disease. While it’s still possible to contract diseases like chickenpox or measles, the widespread vaccination in the U.S. makes it difficult for individual cases to turn into outbreaks (or pandemics).
Herd immunity can also occur when many individuals have previously contracted a disease and developed antibodies that prevent reinfection. Since there’s no vaccine for COVID-19 yet, some people are hoping that we can achieve herd immunity through this method. However, as Gypsyamber D’Souza and David Dowdy, epidemiology professors at the Johns Hopkins Bloomberg School of Public Health, explain, individuals who’ve recovered from COVID-19 may only have immunity for “months to years.” We don’t have enough data on how reinfection works with this coronavirus, but it is known that reinfection can happen with other coronaviruses. In short, relying on this approach for herd immunity isn’t advisable.
Moreover, experts estimate that at least 70 percent of the population would need to be immune to COVID-19 for herd immunity to be effective. If people were to intentionally become infected to gain immunity, our healthcare system would be overwhelmed with cases, and the death toll would be catastrophic.
In conclusion: The most effective way to overcome COVID-19 is to practice social distancing, wear a mask, and wait for a vaccine to become available.
