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FRONTIERS • PUBLIC HEALTH
Herd Immunity: The Foolproof Solution to COVID-19 Writer: Ricky Illindala • Editor: Akshay Govindan
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t has been nearly eight months of social distancing and mask-wearing since the coronavirus first started spreading rapidly in the US. Initially, many states predicted that a four to six week mandatory quarantine would halt the spread of the virus and allow us to return to normalcy. However, that was far from reality. Initial forecasts predicted that we would get over the pandemic during the summer, but now those forecasts have changed. The supposed “end” to the coronavirus pandemic has been delayed, and delayed, until the one question on almost everyone’s mind is: “When will this all end?” One potential ending is when the population becomes herd immune to the coronavirus. Herd immunity is a state in which a population becomes immune to a disease, where the risk of the disease continuing to spread is eliminated or greatly reduced due to enough, but not necessarily all, people in a population gaining immunity [4]. The percentage of immune people in the population required for herd immunity is known as the herd immunity threshold [10]. Not every person in a population is necessarily immune, but enough people are immune that they serve as a barrier to disease spread, which greatly lowers the rate of infection. Generally, there are two primary pathways to gaining herd immunity: vaccination or mass
As a result, vaccines protect both the person who is vaccinated as well as anyone else they might contact.
infection. Vaccines are drugs that are administered as a pre-emptive defense against a pathogen. As more people in a population are vaccinated against a disease, they can no longer contract the infection nor spread it to someone else. As a result, vaccines protect both the person who is vaccinated as well as anyone else they might contact. This makes vaccines very effective in achieving herd immunity in a population [6]. However, vaccines are a recent discovery in the scope of human history. Prior to the discovery of vaccines, herd immunity was achieved through more natural means: mass infection. This process is exactly as it sounds: as a disease spreads throughout a population, individuals will develop a resistance to the disease and be immune after the disease has run its course. However, the caveat is that this pathway could cause widespread illness in the population and potentially death [1]. For this reason, finding a vaccine to rapidly immunize a population is of the utmost priority when confronted with novel diseases. A key historic example of the importance of vaccination in achieving herd immunity was the spread of polio during the first half of the 20th century. The polio virus initially emerged through sudden simultaneous outbreaks in Europe and the United States during the late 1800s. Epidemics repeated year after year, with cases rapidly rising to nearly 25 cases per 100,000 people from 1945 to 1954 [9]. Even though mass infections keep occurring, these epidemics affect smaller numbers of people, preventing the population from developing widespread
immunity. This resulted in an inability to build up herd immunity, allowing polio to reappear and spread illness and death through the affected populations, year after year. The course of the polio virus did not drastically change until the appearance of the inactivated polio vaccine in 1955 and oral polio vaccine in 1961. The number of annual paralytic cases were greater than 10,000 in the years prior to 1955, but the introduction of both vaccines dropped the annual number of cases to less than 100
For this reason, finding a vaccine to rapidly immunize a population is of the utmost priority when confronted with novel diseases.
by 1964 [9]. This highlights another significant danger with mass infection: it is not a foolproof method of obtaining herd immunity. Unfortunately, we haven’t been able to produce a vaccine yet to rapidly curb the COVID-19 pandemic. However, we have been seeing mass infection occurring throughout the US. Hypothetically, if mass infection continued to occur without a vaccine in the near future, could we still reach herd immunity? The answer is unclear. Given that we have no vaccine in this scenario, the only way for people to gain immunity is by contracting the coronavirus and surviving until their body develops immunity against it. To determine the
