Three different lots of measles vaccines produced with the Biken CAM-70 virus strain were requested from the central cold store of the Public Health Department of the State of S. Paulo, Brazil, and assays on photosensitivity at 2-8° C, and on stability at 28, 36.5 and 45° C were carried out to find out for how long these vaccines would maintain their minimum potency, established as being 3.70 log10 or 5000 TCID50 (50% tissue culture infective dose ) per human dose. The analysis of the adjusted straight regression lines indicated that, with the passage of time, the potency of lyophilized or reconstituted vaccines, as well as of vaccines exposed to or protected from light decreased. Light-exposed vaccines, however, became less potent than vaccines protected from the light. None of the vaccine lots studied, reconstituted and stored at 2-8° C, exhibited homogeneity as to sensitivity to light. When freeze-dried vaccines had their photosensitivity studied at 2-8° C, lots 1 and 2 presented greater thermal degradation when exposed to light than when protected from it. However, in both instances, it was found that potency fell bellow that taken as minimum for the Biken CAM-70 virus strain. At all other temperatures considered, even when protected from light, lots 1 and 2 did not retain the minimum potency. Lot 3 kept the expected stability for 60 days at 2-8° C when protected from light and for 40 days when unprotected, but its thermal degradation at other temperatures was more intense (28° C: 5 days; 36.5° C: 2 days; 45° C: 0.5 day). Taking into account the potency that measles vaccines produced with the Biken CAM-70 virus strain are required to contain in order to induce effective immunity, the three vaccine lots studied were found to possess low thermal stability and to lack homogeneity both in the freeze-dried as well as in the reconstituted form.
Measles vaccine; Evaluation studies; Photosensitivity; Thermal stability
