What is Herd Immunity?


What is it?

–Herd or Community Immunity is when a sufficient proportion of a population has become immune to an infectious disease agent such that person-to-person spread is unlikely or unsustainable.

How is Community Immunity achieved?

–Recovery from illness

•Low risk agent - “Chicken Pox parties”

•Hazardous if high-risk infection

–Vaccination programs

•Live attenuated, inactivated or fractionated virus or bacteria that generates an active immune response

–Duration of protection (years) may vary – series or booster

–Passive immunity

•Temporary protection (months) through antibody administration

–Maternal to fetal circulation

–Gamma Globulin for Hepatitis A, Rabies Immune Globulin administration


–Vaccine effectiveness

•Mumps outbreak onboard USS Fort McHenry 2019

–Vaccine refusal

•Highly contagious agent - higher community immune threshold

–Temporal degradation

•Immune titer – blood draw for lab testing

•Booster administration

•Recruit populations, college students

–Agent evolution/modulation

•Seasonal Influenza

–Agent Na├»ve population

•Impact of smallpox on Native American populations


CAPT William C. Brunner
Medical Corps, U.S. Navy
Force Surgeon
Marine Forces Reserve
Marine Forces North