Written by Jacqueline Slobin, University of Virginia & Spencer Lee, New York University
- Herd immunity occurs when a large percentage of a population is immune to a disease, making its spread within that population highly unlikely.
- We need at least 75% of the United States population to be immune to COVID-19 in order to achieve herd immunity and return to normalcy.
- So far, only 5.3 million Americans have received the Covid-19 vaccine. We will need at least 242.2 million more people to get vaccinated in the coming months for the pandemic to end.
What does herd immunity mean?
The World Health Organization defines herd immunity, also known as population immunity, as the indirect protection from an infectious disease that occurs when a population is immune to the disease itself through vaccination or from past infection.
In other words, herd immunity is the immunity conferred on members of a population when the majority of the population has been vaccinated or already has some immunity because they have been previously infected with the disease.
When herd immunity is achieved, disease transmission slows or stops completely because members of the population are unable to infect each other.
Herd immunity against COVID-19 should be achieved by protecting people through widespread vaccination efforts, NOT exposing them to the pathogen that causes the disease.
In the United States, two vaccines have received FDA-approval: Pfizer and Moderna. Herd immunity will depend on the number of people able and willing to receive these vaccinations.
Source: Oxford Vaccine Group
Why can’t we just wait until we are all naturally infected with Covid-19?
With some, less severe diseases, such as the chicken pox, some people might have exposed themselves intentionally as a way of achieving immunity prior to vaccine development.
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However, COVID-19 carries a high risk of severe disease and death. As compared to the chicken pox or even the flu, an individual is much more likely to experience severe symptoms — both long and short-term — and even death when becoming infected with the coronavirus. Therefore, the benefits of exposing yourself do not outweigh these risks.
Moreover, achieving herd immunity through natural infection would lead to the death of millions of people, overwhelm hospital systems, and leave many people with long term chronic illnesses.
How many people need to be vaccinated in order to reach herd immunity?
The actual number of people that need to develop immunity in order for the herd immunity threshold to be achieved varies among diseases and depends largely on how infectious the disease itself is.
For COVID-19, epidemiologists originally estimated that 60 to 70 percent of the population would need to be vaccinated; however, in a December 16th interview with CNBC Dr. Anthony S. Fauci cited “75 to 80-plus percent.”
With the United States population consisting of approximately 330 million individuals, this would mean that at least 247.5 million people would need to receive both doses of the Pfizer or Moderna vaccines for herd immunity to be actualized.
When can we expect to achieve herd immunity?
To contextualize a timeline of when the United States might expect to achieve herd immunity and thereby return to some normalcy, it might be wise to understand the herd immunity timeline for other diseases.
For instance, during the 2009 H1N1 Pandemic, it took approximately 5 to 6 months for widespread vaccine administration to occur within the United States, according to the Centers For Disease Control. 10 months later in August 2010, the WHO declared the H1N1 pandemic over as herd immunity had been achieved. If all goes accordingly, we can therefore expect to achieve herd immunity from late summer to end of 2021.
However, as of January 6, only 5.3 million Americans had received the COVID-19 vaccine. Unless more efforts are made to increase dissemination, achieving herd immunity will likely take longer than expected.
How close are we to achieving herd immunity?
At minimum, the United States will need to vaccinate 247.5 million Americans to achieve the lower bounds of herd immunity.
Only 5.3 million Americans have been vaccinated thus far, so based on vaccinations alone, we are only 2.2% of the way to achieving herd immunity. Herein, the need for widespread vaccinations is evident.
Receiving the COVID-19 vaccination is a choice, but the willingness of more Americans to do so will only help us end this pandemic sooner. If you are hesitant about receiving the vaccine, read our article about COVID-19 vaccine myths debunked.