Authors
Benny PV, Editor, IMA Kerala Medical Journal
Abstract
Introduction: Herd immunity is a crucial epidemic theory concept, signifying population-level protection against pathogen transmission when enough individuals are immune. For COVID-19, achieving herd immunity, via natural infection or vaccination, is considered the ultimate path to control its public health threat.
Key Concepts: The effectiveness of herd immunity hinges on the immune population percentage and the reproduction numbers (R0/Rt). R0 > 1 implies increasing transmission; R0 < 1, decline. The critical immunity level (Pcrit) needed to stop spread is Pcrit = 1 - (1/Rt). With an estimated Covid-19 R0 of 2-3, around 70% population immunity is generally required. The text also notes potential partial immunity from prior seasonal coronavirus infections. Strategies and Challenges: Achieving herd immunity solely through natural infection risks high mortality. Vaccination is the preferred method, extending indirect protection. The article compares mitigation (slowing transmission, allowing herd immunity but risking early high mortality) and suppression strategies (reversing spread, but risking future outbreaks if immunity isn’t achieved, ideally by vaccination).
Conclusion: The choice of strategy involves balancing immediate health burdens, mortality, and long-term protection. An effective vaccine is pivotal for safe herd immunity development within a suppression framework.