Herd immunity and the harm principle: Too narrow or too broad

In this commentary, I will contend that one of Pierik and Verweij's central arguments for vaccine mandates faces significant obstacles because of their attempt to apply Mill's harm principle. More specifically, they argue that vaccine refusal is harmful because of its relationship to the collective good of herd immunity. I suggest that Pierik and Verweij oscillate between two interpretations of the harm principle: a narrow interpretation and a broad one. The narrow interpretation, however, does not justify mandates because it is implausible that one individual's act of vaccine refusal makes a meaningful difference to whether herd immunity is achieved. The broad interpretation avoids this problem, but it risks abandoning the authors' aspiration to advance a distinctively liberal argument. I conclude that those who wish to defend vaccine mandates by appealing to their role in achieving or maintaining herd immunity face a choice: they need to either (i) find argumentative resources within the liberal tradition that are more promising than the harm principle or (ii) develop defenses that are not liberal but indicate why this does not constitute a problem.