Chickenpox

Researchers have long noted the seasonality of chickenpox. According to their research, chickenpox cases occur at their lowest rate during September. Numbers of cases increase throughout the autumn, peak in March and April, and then fall sharply once summer begins. This cycle corresponds to the typical school year in the United States. When children go back to school in the fall, they begin to spread the disease; when summer comes and school ends, cases of chickenpox diminish. A typical "mini-epidemic" within a school occurs when one child contracts chickenpox. This child rapidly infects other susceptible children. Soon, all the children who had not had chickenpox contract the disease within two or three cycles of transmission. It is not uncommon for high numbers of children to be infected during one "mini-epidemic;" one school with 69 children reported that the disease struck 67 of these students.