system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
A 1-year-old immigrant girl has not received any recommended vaccines since birth. She attends daycare and remains healthy despite her daily association with several other children for the past 3 months at a home day-care facility. Which of the following phenomena explains why she has not contracted any vaccine-preventable diseases such as measles, diphtheria, or pertussis?
assistant
Herd immunity