Field Trials of Methisazone as a Prophylactic Agent Against Smallpox1

Heiner, G. G. (Institute of International Medicine, Univ. of Maryland School of Medicine, Baltimore, Md. 21201), N. Fatima, P. K. Russell, A. T. Haase, N. Ahmad, N. Mohammed, D. B. Thomas, T. M. Mack, M. M. Khan, G. L. Knatterud, R. L. Anthony and F. R. McCrumb, Jr. Field trials of methisazone as a prophylactic agent against smallpox. Amer J Epidem 94: 435–449, 1971.—Three field trials of methisazone as a prophylactic agent against smallpox were carried out in West Pakistan between 1964 and 1970. Subjects were household and compound contacts of smallpox cases, assigned to drug or placebo groups by previously randomized schedules. Overall attack rates were 2.7% (7 of 262 contacts) and 5.0% (13 of 260 contacts), respectively, in the drug and placebo groups, a difference that was not statistically significant. Previously vaccinated contacts showed low and almost identical secondary attack rates of 1.2% (3/244) and 1.3% (3/238) in the drug and placebo groups. Unvaccinated contacts had attack rates of 22.2% (4/18) in the methisazone group and 45.5% 10/22) in the placebo group, suggesting a possible protective effect of the drug. On the other hand, no differences in mortality or morbidity were noted between cases in treated and untreated groups. Comparison of paired sera of 13 contacts in the drug group and 12 in the placebo group provided no evidence of a suppressive effect of methisazone on the immunologic response to vaccination. Results of previous studies of methisazone have been compared.