As part of the clinical validation process of a new working seed of a licensed yellow fever vaccine (new working seed PV26, Stamaril; Pasteur Mérieux Connaught, Lyon, France), the immunogenicity and safety of two batches of this vaccine (PM-YF) were compared with those of another commercially available vaccine (Arilvax; Evans Medical-Wellcome, Liverpool, United Kingdom) in 211 healthy adults. While the geometric mean titer values at days 10–14 and day 28 after vaccination were higher in the PM-YF group, the vaccines provided equivalent seroprotection (titers 1/10) one month after a single vaccine dose (100% PM-YF versus 99% W-YF; P 0.001, by one-sided equivalence test). Both vaccines were safe. There were no serious local or systemic reactions reported, nor any clinically significant hepatic function abnormalities associated with the use of either vaccine. These two 17D yellow fever vaccines from different European vaccine manufacturers were highly immunogenic and safe, and provided equivalent seroprotection.

Yellow fever is a viral tropical disease, occurring endemically, with periodic epidemics, in the Americas and Africa. The yellow fever virus, a member of the Flavivirus family, is mosquito borne, and in humans produces a clinical disease characterized by sudden onset of fever, followed by hepatorenal dysfunction and hemorrhage. Epidemics can be associated with attack rates of 33% and mortality rates of more than 75%. 1, 2 Since 1980, there has been a sudden re-emergence of this disease in Africa and South America, with a total of 18,735 cases and 4,522 deaths reported world-wide between 1987 and 1991. This represents the highest level of yellow fever activity reported to the World Health Organization (WHO) over any five-year period since reporting began in 1948, 3 and emphasizes the continued need for effective control through vaccination and other public health measures. The Advisory Committee on Immunization Practice of the Centers for Disease Control and Prevention (Atlanta, GA) and the WHO now recommend that yellow fever vaccine be administered to all persons 9 months of age if they are living in or travelling to areas of South America and Africa where yellow fever is officially reported. 4, 5 The history of the yellow fever vaccine is extensive; yellow fever was the third human disease (after small pox and rabies) to be controlled by vaccination. A live, attenuated virus (17D), derived from a human isolate (Asibi), and attenuated by serial passage in mouse brain and chick embryo cells6, 7 has been used safely and effectively as a vaccine for more than 50 years. Due to some early problems with this vaccine, such as overattenuation or reversion to virulence, that were related to inconsistent manufacturing processes, 8, 9 in 1945 WHO proposed the use of a seed-lot system in which a primary seed is used to generate secondary seeds that are then used by the different laboratories to produce vaccine batches. 10 Twelve institutes around the world manufacturing yellow fever vaccine from one of three different 17D vaccine strains (17D-204, 17DD, and 17D-204-WHO) are approved by WHO for certification for international travel. 11