Very sure. The fatality rate is negligible and the boost is significant. See https://www.cnn.com/2010/HEALTH/12/06/daycare.kids/index.html https://www.cnn.com

Very sure. The fatality rate is negligible and the boost is significant. See https://www.cnn.com/2010/HEALTH/12/06/daycare.kids/index.html https://www.cnn.com/2010/HEALTH/12/06/daycare.kids/index.htm... for a random news article reporting on a similar result only with kids getting sick in daycare. Being exposed to diseases early builds immunity later.