647797 external_news 1622141173 1622141173 Even as health officials continue to try to calculate — and communicate — when herd immunity might happen, they have to contend with both public misunderstanding of the term and scientific disagreement over what it means. Even within public health circles, “some of our colleagues have disagreed with one another” on the definition of herd immunity, says Joshua Weitz, Patton Distinguished Professor and Co-Director of the Interdisciplinary Ph.D. in Quantitative Biosciences at the School of Biological Sciences. Changes in behavior can lead to declines in cases, he says, “that do not imply that the population has reached herd immunity.” Populations develop immunity through a combination of vaccination and natural infections, Weitz says, and the safe and ethical route to reach herd immunity is through vaccinations.

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