students were four times as likely

Social networks were apparently a more significant means of transmission than seating arrangements. Students were four times as likely to play with children of the same sex as with those of the opposite sex, and following this pattern, boys were more likely to catch the flu from other boys, and girls from other girls.

and

“Our social networks shape disease spread,” said Simon Cauchemez, the lead author. “And we can quantify the role of social networks.”

(source and the full report is here.