A massive outbreak of mumps among Orthodox Jews in 2009 was due to the system of learning in yeshivas, according to a report by NPR.
Over 3,5000 people got sick after an 11 year-old boy came home from the UK with the illness in June of 2009, prompting New York authorities to issue an additional shot of the measles-mumps-rubella vaccine to children who were already considered vaccinated.
Officials at the Center for Disease Control (CDC) determined that sitting for hours at a time with a chavruta – learning partner – could bombard the system with more of the illness than for which the vaccines generally provide immunity.