The city Health Department is investigating an outbreak of chickenpox that has infected infants and young children in the Orthodox Jewish community of Williamsburg, Brooklyn.

“There have been 75 reports of persons with varicella [chicken pox] who became ill during or after March 2016. The median age of patients is 3 years (range 0 to 10 years),” health officials said a Monday alert to medical providers.

Of those who had chickenpox, 72 percent were not vaccinated and 14 percent had not yet received the full recommended number of doses of vaccine.

Chickenpox is an infectious disease that causes a mild fever and rash of itchy lesions or blisters.