The incidence of variola minor during an outbreak was analyzed by use of mathematical model B proposed by Chelsky and Angulo. Several parameters were estimated. Among these, the propagating rate (ratio of receptor cases to source cases) seems to predict the outbreak decline better than inspection of the incidence curve. The estimated mean generation interval (18.6 days) supports the thesis that variola minor is not transmitted at onset of illness but, on the average, about 4 days later. The ratio of clinical to subclinical infections (about 1 to 1) approximates those ratios found in serological surveys of variola minor and variola major outbreaks.
Present address: Instituto Adolfo Lutz, São Paulo, S.P., Brazil.