One of the most widely known risks linked to the COVID-19 vaccine is myocarditis, especially in young males — and now a new Stanford study has shed some light on why this rare effect can occur.

Obesity is uncommon among Hadza hunter-gatherers in Tanzania, Tsimane forager-farmers in Bolivia, Tuvan herder-farmers in Siberia, and other people in less-developed nations. But it’s widespread among ...