[Use of the monkey pox virus for evaluating the intensity of the immunity against smallpox in experiments on M. rhesus]

Monkeypox virus causing in M, rhesus upon aerogenic infection a disease similar to human varioloid was used to evaluate the intensity of immunity against smallpox in immunized M. rhesus monkeys. Postvaccination immunity was solid in all the animals vaccinated intradermally or orally. In 2 out of 14 monkeys immunized orally, however, the immunity was partially overcome. Neutralizing antibody titers in these two monkeys were 1:5 and 1:25, respectively. This agreed with the observations made in Pakistan indicating the possibility that some humans having serum neutralizing antibody titers up to 1:32 could contract smallpox and develop the disease.