It was recognized as a naturally occurring phenomenon in the 1930s when it was observed that after a significant number of children had become immune to measles, the number of new infections temporarily decreased, including among susceptible children.
Quedou recoñecido coma un fenómeno de ocorrencia natural na década dos anos 1930 ó observarse que tras que un número significativo de nenos se tornaron inmunes ó sarampelo, o número de novas infeccións diminuíu temporalmente, incluíndo a nenos susceptibles de contaxio.