infection prevention
By Sue Barnes , RN , CIC , FAPIC
Herd Immunity and COVID-19
When a large percentage of a community is immune to an infectious disease , ongoing transmission of the disease is unlikely . This state is called " herd immunity ," and it can be achieved through vaccination ( vaccine-induced immunity ) and through infection with the disease ( natural immunity ). It is important to note that by reducing viral transmission , herd immunity provides protection to those who cannot be vaccinated , such as newborns and immunocompromised individuals . 1
The number of people required to be immune to achieve herd immunity is based on the contagiousness of the disease . Those infectious diseases that spread easily , such as measles , require a higher number of immune individuals in a community to reach
Experts estimate that in the United States , more than
200 million people ( 70 percent of the population ) would have to recover from COVID-19 and develop effective natural immunity in order to achieve herd immunity , thereby halting the epidemic . 2 herd immunity . COVID-19 is also a very contagious disease . Experts estimate that in the United States , more than 200 million people ( 70 percent of the population ) would have to recover from COVID-19 and develop effective natural immunity in order to achieve herd immunity , thereby halting the epidemic . 2
There are a lot of unknowns with COVID-19 which add complications to the goal of achieving herd immunity . Most importantly , we do not have a vaccine and may not for some time . Additionally , we do not know if immunity is always conferred by COVID-19 infection , nor which people develop natural immunity after infection , and how long immunity might last . Even once a vaccine is developed , there are variables that will impact its effect on the pandemic . These include how effective the vaccine is , how many vaccine doses will be available for distribution , and how
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many people are willing to get vaccinated . This last variable is anticipated to be a significant challenge given the number of people who refuse to receive the annual influenza vaccination . And of course , even with a vaccine , until herd immunity is achieved , cases introduced by those traveling from outside of the U . S . will contribute to the ongoing COVID-19 epidemic here .
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Given the lack of a unified national response to the COVID-19 pandemic in the U . S ., a wide spectrum of approaches can be seen relative to prevention tactics from state to state . This has also resulted in the highest case and death count globally , and dissent among various experts regarding the best method of achieving herd immunity . 4 On the one hand , there is the Great Barrington Declaration . This is a statement written by three public health experts which supports achieving herd immunity by allowing COVID-19 to spread in the young and healthy population where it is less likely to be deadly . The three experts suggest that the current COVID-19 prevention measures are resulting in greater harms than the pandemic , including economic instability ,
lower childhood vaccination rates , fewer health screenings , and deteriorating mental health . 5
This Declaration was denounced by the John Snow Memorandum , which was published in response and signed by 6,900 scientists and health experts . 6 The memorandum recommends that restrictions ( not lockdowns ) should be continued , in addition to social and economic programs and vaccine development . These experts explain that the primary concern with permitting spread of COVID-19 is that it would lead to the death of 1 million to 2 million people , without necessarily speeding up society ’ s return to business as usual . In addition , if so many people become sick with COVID-19 at one time , hospitals would become quickly overwhelmed .
Many medical professionals use the term “ herd protection ” instead of herd immunity , because the phenomenon doesn ’ t actually result in immunity to the virus . Instead it reduces the risk that non-immune people will come into contact with the virus . Applying the concept of herd immunity through community spread of SARS CoV2 , would be based on the unproven assumption that anyone who survives an infection will become immune . From studies of the pandemic to date , it does seem that some kind of immunity seems to follow infection , but it is unclear how long and for which people this occurs . And we don ’ t yet have a definitive method to measure immunity to SARS CoV2 virus . 7
In the absence of a national approach to the pandemic , it may be prudent to look to the clinical professionals for guidance ( John Snow Memorandum ), versus those in public health sector ( the Barrington Declaration ) if the two are not in alignment . Clinical experts not only have training and experience regarding infectious diseases they are also at the front lines , observing first-hand what is happening with the pandemic . As concluded by the John Snow Memorandum , herd immunity for COVID-19 cannot safely be achieved with natural immunity alone but must be supplemented with vaccine induced immunity once an effective vaccine is widely available . In the meantime , local governments will continue to determine what restrictions on business are needed , supplementing social distancing and mask / face coverings , to contain the pandemic .
References :
1 . CDC . https :// www . cdc . gov / vaccines / vac-gen / immunity-types . htm Last accessed November 3 , 2020 .
2 . Mayo . https :// www . mayoclinic . org / diseases-conditions / coronavirus / in-depth / herd-immunity-and-coronavirus / art-20486808 Accessed Nov , 3 , 2020 .
3 . The Lancet . https :// doi . org / 10.1016 / S0140-6736 ( 20 ) 32153-x Accessed Nov . 3 , 2020 .
4 . Altman D . Understanding the US failure on coronavirus . BMJ 2020 ; 370 : m3417 .
DOI : https :// doi . org / 10.1136 / bmj . m3417 ( Published Sept . 14 , 2020 ). 5 . Great Barrington Declaration . https :// gbdeclaration . org / Accessed Nov , 3 , 2020 . 6 . John Snow Memorandum . https :// www . johnsnowmemo . com / Accessed
Nov . 3 , 2020 .
7 . Aschwanden C . The false promise of herd immunity for COVID-19 . Nature online ; Oct . 21 , 2020 . DOI : https :// doi . org / 10.1038 / d41586-020-02948-4 Accessed Nov . 3 , 2020 .