083 Thermostabilization of measles vaccines using preservation by vaporization

Abstract

Despite the availability of safe and effective vaccines against the measles virus, an estimated 25–30 million cases of measles infection still occur annually according to the World Health Organization. Furthermore, measles infection remains a leading cause of death among young children worldwide. Currently, all commercial measles vaccines (MV) are live-attenuated strains. Because of their inherent instability at ambient temperatures, they are formulated as a lyophilized powder that requires reconstitution prior to subcutaneous injection. However, the standard lyophilization method used in vaccine production reduces the initial titer of the vaccine virus approximately 10-fold and results in vaccines that experience rapid titer loss (more than 10-fold per month) at 37 °C. Over the last decade, the authors have carried out numerous attempts to formulate a thermostable Edmonston-Zagreb MV using foam drying instead of freeze-drying. We have demonstrated that our Preservation by Vaporization (PBV, US Patent Application No. 20080229609 A1) foam drying technology allows for effective stabilization of MV at 37 °C with titer loss below 0.5 logs after drying. For example, MV produced in chick embryo fibroblasts (supplied by Berna Biotech) was stable for at least 6 months, MV produced in human diploid cells (supplied by the Serum Institute of India (SII)) was stable for at least 2 months, and MV produced in Vero cells at the CDC was stable for at least 1 year. After reviewing our results, we have found that different vaccine production methods can affect the initial yield of MV after PBV drying. For example, after foam drying of MV produced in human diploid cells (supplied by the SII), we lost about one log of titer, whereas we lost less than 0.5 logs of titer after PBV drying of MV produced in chick embryo fibroblasts (supplied by Berna Biotech). Furthermore, we found that MV produced in Vero cells after two passages (yielding a higher virus concentration) had an initial yield titer 0.5 logs higher than similar vaccine produced after a single passage in Vero cells. In previous studies with unpurified viral vaccines, such as BVD and BRSV animal virus vaccines, we observed about a log of titer loss after foam drying; however, with purified human viral vaccines (YF-17D, MVA) we did not observe any significant loss after foam drying (see http://ncnv.org/wp-content/uploads/2012/10/1540-Bronshtein.pdf ). Based on our cumulative experience, we believe that the variability in titer loss of MV after foam drying (initial yield) and subsequent storage at 37 °C may be influenced by the type of cells used for vaccine production, the number of passages used for vaccine production, the extent of vaccine dilution in preservation solution before drying, and the degree of vaccine purification after production (most MV are not purified). One potential explanation for the titer loss we have observed with unpurified MV after drying could be highly reactive molecules remaining in the media after vaccine production. The mechanism of this effect is currently under investigation, although some preliminary data suggest that a high concentration of Ca2+ ion could contribute to this effect. Source of funding: Research is supported by CDC SBIR contract # 200-2012-53276. Conflict of interest: None declared. victorb@uptsd.com