August 12, 2024
As we’ve now watched the COVID-19 vaccine become widely available and are (hopefully!) working our way toward the end of the pandemic, there is another concept that has also become fresh on everyone’s mind: herd immunity. Read on for more information on what herd immunity is and whether it plays a role in ending the COVID-19 pandemic.
What Exactly is Herd Immunity?
Herd immunity occurs when a large majority of the population becomes immune to a disease.1 Think of it this way: if 90 percent of those in a community are immune, that leaves only 10 percent who are eligible to contract and spread a particular virus. Once this occurs, a virus would have an increasingly difficult time spreading, causing infection rates to start to decline and the population at large becomes protected (even those who are not immune or cannot get vaccinated).
How is Herd Immunity Achieved?
Two ways, really: either organically through natural infection or through the development of a vaccine.2
Once your body has been exposed to a virus, antibodies are created to ward off the infection. After you recover from being ill, the antibodies are retained and protect you against getting sick again.
Relying solely on recovery from natural infection to achieve herd immunity from COVID-19 presents significant challenges, though. Currently there is a debate on how long natural antibodies last against reinfection. Furthermore, the sheer number of people that would need to be exposed to the virus could create significant problems for the health system.
Vaccines, on the other hand, result in immunity from a virus without contracting the virus itself and over the years have been successful in controlling diseases like smallpox and polio, among others. Some vaccines will also require additional doses (“booster shots”) to maintain an individual’s immunity over time.
“When considering major diseases that have affected the population to the magnitude that COVID-19 has, achieving herd immunity is really only possible through the use of a vaccine,” said Dr. Nancie Fitch, Area Medical Director, MedExpress.
When Can We Expect to Achieve Herd Immunity From COVID-19?
In short, it’s complicated.
While experts are hopeful that we will reach herd immunity eventually, we still have work to do. Plus, the novelty of the COVID-19 virus hasn’t made it easy for researchers to fully understand what they are dealing with yet. It is unclear what percentage of the population will need to be immune to achieve herd immunity or how long that will take. Most agree that we will need to reach the 75-80 percent mark of the eligible population, but because the threshold is impacted by how contagious a given virus is, a level as high as 90 percent3 may be necessary.
Such was the case with measles, a highly infectious disease that took a 95 percent vaccination rate to reach herd immunity.4 The measles vaccine has been remarkably effective since it was introduced, though, enabling the United States to maintain its measles elimination status for nearly 20 years.5 By following the Centers for Disease Control and Prevention’s (CDC) routine immunization schedule, long term herd immunity has been maintained.
We can be cautiously optimistic regarding herd immunity, but in the meantime, we should focus on vaccinating as many people as possible, say epidemiologists at Stanford Medicine.6 Because regardless of what the magic number threshold for herd immunity is, higher levels of immunizations will continue to bring the highest and quickest benefits.
This content was medically reviewed by a MedExpress physician.
Originally published August 2021. Updated August 2024.
References:
1 Mayo Clinic. Herd Immunity and COVID-19 (Coronavirus): What You Need to Know. Last updated June 9, 2021. Accessed July 8, 2021.
2 WebMD. What is Herd Immunity? Last updated December 13, 2020. Accessed July 8, 2021.
3 Johns Hopkins Bloomberg School of Public Health. What is Herd Immunity and How Can We Achieve It With COVID-19? Last updated April 6, 2021. Accessed July 9, 2021.
4 World Health Organization. Coronavirus Disease (COVID-19): Herd Immunity, Lockdowns and COVID-19. Last updated December 31, 2020. Accessed July 13, 2021.
5 Centers for Disease Control and Prevention. History of Measles. Last updated May 9, 2024. Accessed August 12, 2024.
6 Stanford Medicine. With Herd Immunity Elusive, Vaccination Best Defense Against COVID-19, Stanford Epidemiologist Says. Last updated May 27, 2021. Accessed July 9, 2021.