Intuitively getting vaccinated does not just protect you but protects those around you but proving this can be challenging with so many confounding factors.

This week Fred Goldstein and I look at the concept of Herd Immunity and especially at the local level, and in the case of an elegant paper looking at data out of Sweden at the family unit level. The study benefits from the fact that their national health system has data on basically everyone who lives in that country, leading to a cohort of just under 1.8 million people.

The results were convincing. Among families that have two people living together, having one of them be immunized reduced the rate of infection in the other person by 45%. Larger families showed an increased response.

Like all papers, this should be read with a critical eye and we discuss how to approach the data from this study and others and review some of the limitations from the study and what that means for the results.

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