Herd immunity, vaccination and moral obligation

Area of Science:

• Public Health
• Epidemiology
• Bioethics

Background:

• Herd immunity is frequently cited to justify mandatory vaccination policies.
• The concept of herd immunity is ambiguous and has multiple interpretations.
• Different interpretations of herd immunity influence ethical considerations and policy decisions.

Purpose of the Study:

• To analyze the multiple referents of 'herd immunity'.
• To examine how different interpretations of herd immunity affect ethical obligations for vaccination.
• To evaluate the justification for coercive vaccine policies based on the concept of herd immunity.

Main Methods:

• Conceptual analysis of the term 'herd immunity'.
• Examination of epidemiological outcomes (elimination vs. endemic equilibrium).
• Ethical evaluation of vaccination obligations and coercion.

Main Results:

• 'Herd immunity' can refer to the threshold for epidemic decline, population immunity percentage, or indirect benefits.
• The validity of herd immunity arguments varies by pathogen, with optimal conditions not applying to all diseases.
• For pathogens with waning immunity or antigenic variation (e.g., SARS-CoV-2), mass vaccination may only delay infections, weakening the obligation for individual contribution and justifying coercion less.

Conclusions:

• The ethical justification for coercive vaccination policies is contingent on the specific interpretation of 'herd immunity' and pathogen characteristics.
• Ambiguity in the term 'herd immunity' complicates its application in public health ethics.
• Coercive vaccine policies are less justifiable for pathogens where herd immunity thresholds are not readily achievable or where reinfection is common.