An inactivated eastern equine encephalomyelitis vaccine propagated in chick-embryo cell culture. II. Clinical and serologic responses in man.

A formalin-inactivated Eastern equine encephalomyelitis vaccine was prepared from the PE-6 strain virus, propagated in primary chick-embryo cell cultures maintained with Medium 199 containing 0.25% human serum albumin. To effect an increase in antigenic mass per unit volume of fluid harvest, we used the pooled fluids from the first tissue-culture passage as maintenance medium for two additional passages. A formalin concentration of 1:2,000 (0.05%) at 37°C was used for inactivation of the virus suspension. Tests on the "in-process" and final vaccine documented the safety and sterility. Tests of potency on the final lyophilized product in hamsters and guinea pigs yielded EDB0 values of 0.009 ml and 0.012 ml, respectively. Recent assays have revealed no change in potency after storage of the fin?! product for 17 months at -20°C. Currently there is no commercial source of Eastern equine encephalomyelitis (EEE) vaccine approved for use in man. For many years investigators and field workers at risk to infection with EEE virus could obtain only limited quantities of a vaccine prepared from infected whole-chick embryos by the method of Randall et al.' When production and distribution of this vaccine was abruptly halted in 1965-66, the U. S. Army Medical Unit assumed responsibility for production and testing of an EEE vaccine for limited use in man. As part of an over-all program concerned with vaccine research and development, production of the EEE vaccine progressed smoothly and, by necessity, rapidly. This paper, the first of a series, describes the production and testing of the new EEE vaccine. MATERIALS AND METHODS