The National Network for Immunization Information (NNii) provides up-to-date, science-based information to healthcare professionals, the media, and the public: everyone who needs to know the facts about vaccines and immunization.

Immunization Issues

Community Immunity

Unimmunized persons are protected—indirectly—against some infectious diseases by being surrounded by immunized persons. This is known as community (or “herd”) immunity. Why is community immunity important for public health?


Immunization Science

Impact of Rotavirus Vaccine in Gastroenteritis Hospitalizations

This study describes the reduction in acute gastroenteritis hospitalizations among children after introduction of rotavirus vaccine in the United States.