Herd immunity, vaccination and moral obligation

Abstract

The public health benefits of herd immunity are often used as the justification for coercive vaccine policies. Yet, ‘herd immunity’ as a term has multiple referents, which can result in ambiguity, including regarding its role in ethical arguments. The term ‘herd immunity’ can refer to (1) the herd immunity threshold, at which models predict the decline of an epidemic; (2) the percentage of a population with immunity, whether it exceeds a given threshold or not; and/or (3) the indirect benefit afforded by collective immunity to those who are less immune. Moreover, the accumulation of immune individuals in a population can lead to two different outcomes: elimination (for measles, smallpox, etc) or endemic equilibrium (for COVID-19, influenza, etc). We argue that the strength of a moral obligation for individuals to contribute to herd immunity through vaccination, and by extension the acceptability of coercion, will depend on how ‘herd immunity’ is interpreted as well as facts about a given disease or vaccine. Among other things, not all uses of ‘herd immunity’ are equally valid for all pathogens. The optimal conditions for herd immunity threshold effects, as illustrated by measles, notably do not apply to the many pathogens for which reinfections are ubiquitous (due to waning immunity and/or antigenic variation). For such pathogens, including SARS-CoV-2, mass vaccination can only be expected to delay rather than prevent new infections, in which case the obligation to contribute to herd immunity is much weaker, and coercive policies less justifiable.

Herd immunity to endemic diseases: Historical concepts and implications for public health policy

“…Similarly, young children and healthy young adults are at very low risk of severe COVID‐19. While higher risk groups for vaccine‐preventable diseases should be offered protection from morbidity and mortality via vaccination, this does not necessarily imply the necessity or ethical acceptability of regular booster vaccination of lower risk groups 46,47 . Accepting annual incidence of mild or asymptomatic infection in children and vaccinated adults might in some cases be a lower risk means of maintaining herd immunity than vaccinating children.…”

When Claims of ‘Revisionism’ and ‘Misinformation’ are Themselves Misinformed: Implications for Policy Decision-Making

“…Many ideas for how to protect older people while not mandating lockdowns (of varying severity) have been offered, including by the authors of the GBD (Bhattacharya et al 2020). Finally, "absence of elimination should not be confused with the absence of herd immunity," as it is recognized that "for pathogens [e.g., RSV, influenza, seasonal Coronaviruses, SARS-CoV-2] where immunity from infection or vaccination is relatively ineffective at preventing subsequent (re)infection, accumulation of immune individuals results in the development of an endemic equilibrium… such pathogens continue to circulate, often mutate, and (re)infect members of the population whose immunity wanes over time" (Bullen et al 2023). Indeed, erosion of this endemic equilibrium by immunity debt occurred due to interruption of transmission of endemic infections during the SARS-CoV-2 pandemic (Bullen et al 2023;Cohen et al 2023).…”

“…The phenomenon of original antigenic sin (where the vaccinated cannot mount an adequate immune response to new variants) is another concern, and may account for studies that find negative VE for symptomatic infection over time (Aguilar-Bretones et al 2023;Chemaitelly et al 2023;Altarawneh et al 2022;Lin et al 2023), for the finding in studies of employees at the Cleveland Clinic of an increased risk of COVID-19 associated with an increasing number of previous vaccines received (Shrestha et al 2023a), and of lower risk of COVID-19 in those not being 'up-to-date' on COVID-19 vaccination (i.e., having had at least one dose of a bivalent vaccine) (Shrestha et al 2023b). Overall, non-replicating vaccines for respiratory viruses (such as SARS-CoV-2, without a viremic phase of systemic spread) were known, prior to this pandemic, to be non-sterilizing, to have little effect on transmission, to have waning efficacy over time, and to require RCTs to determine VE for important outcomes (Bullen at al. 2023;Yewdell 2021;Morens et al 2023aMorens et al , 2023b.…”

Effectiveness of A Web-Based Course on Vaccination Competence in Higher Education: The Eduvac Erasmus+ Project

“…Herd immunity is achieved when the majority of individuals are immune to a disease after vaccination. Maintaining herd immunity is vital due to the high contagiousness of many diseases (Bullen et al, 2023). According to a study on COVID-19 vaccination, there is a negative correlation between vaccination hesitancy and individuals without a high school education (Khairat et al, 2022).…”