Dear Colleagues,
 
There have been messages referring to the thermostable PPR vaccine developed at ILRI. I thought it may be helpful to describe the approach, some of the principle results and the current status of the vaccine.
 
We embarked on a comparison of methods described in the literature as having been applied to the thermostablization of morbillivirus vaccines. These included the Thermovac method used to thermostablize RP vaccine based on the use of lactalbumin hydrolysate and sucrose stabilizer and a gentle lyophilization cycle that lasted 72 hours and achieved a product with 1% residual moisture (Mariner et al., 1990; Mariner et al., 1991).  In addition, we examined the use of trehalose in place of sucrose and the use of 10% trehalose alone as a stabilizer. The sucrose and trehalose vaccine preparations for these comparisons were lyophilized in the same machine run to control lyophilization as a variable in the research. Further, we produced Xerovac according to the method described by Worrall et al (2000). We compared all preparations in accelerated stability tests at 37C. All batches were prepared using The Nigeria 75/1 strain produced in Vero cells according to OIE
 norms.
 
The Thermovac method yielded vaccines with the highest level of stability. Three separate lots of vaccine maintained the minimum required titer as a 25 dose vial for 103, 148 and 162 days and had half-lives of 25, 50 and 51 days.
 
In addition, the Thermovac PPR vaccine has been evaluated at 45 and 56C. The minimum required titer for a 25-dose presentation was retained at 45C for 33 days and at 56C for 13 days.
 
Comparisons between batches of vaccine stabilized with 5% lactalbumin hydrolysate (LAH) and 10% sucrose (LAH-S) against vaccine batches stabilized with either 5% LAH and 10% trehalose or just 10% trehalose found that the sucrose stabilized vaccines were more stabile. Sucrose, being more than 10-fold less expensive than trehalose, is preferred excipient.
 
The thermostability of a 25-dose preparation of Xerovac was analyzed at 37C and found to be 22 days and the half-life was 3.7 days. It should be noted that this lot of Xerovac was more stable than the vaccine described by Worrall et al (2000), the only published or publicly available data on Xerovac thermostability. The range of 37C data for 25-dose preparations of Thermovac was 5 to 10-fold greater than Xerovac. Thermovac was also considerably easier to produce and resulted in a more consistent product.
 
As was mentioned in previous E-conference posting, more detailed reporting of results is available in the posters published in the Second Meeting of the Global PPR Research Alliance.
 
During the eradication of rinderpest, the Thermovac process was successfully implemented by three vaccine production laboratories (the National Veterinary Institute of Ethiopia, LANAVET in Cameroon and the Botswana Vaccine Institute) and tens of millions of doses were produced and used in the final eradication effort. The vaccine was used in the field without a cold chain for up to 30 days. Community-based vaccination programs that utilized Thermovac-RP were established in several of the remote pastoral areas that were acting as reservoirs of rinderpest infection. These programs contributed significantly to the completion of eradication. 
 
 
Thermovac PPR is fully compliant with OIE norms. No changes have been made to the viral immunogen or its production process. The stabilizer is unchanged and the lyophilization process is a well-established procedure. The vaccine has sufficient stability for use without a cold chain for up to 30 days and is ready for commercialization in laboratories with production mandates. We have received requests to assist laboratories with commercialization of production, and are working to secure funding to provide technical assistance.
 
We welcome independent measurements of thermostability as part of the commercialization process. We believe that abbreviated thermostability tests should be a component of quality control testing of all vaccines marketed as thermostable products. This was the case for thermostable RP vaccine. Previously, it was agreed at the Joint AU-IBAR/FAO Stakeholders’ meeting convened by FAO Sub-regional Office for Eastern Africa in Addis Ababa, Ethiopia on 25-26 September 2012 to discuss PPR and small ruminants diseases control for building resilience among the pastoralist communities of the Horn of Africa that PANVAC is the appropriate organization in Africa to carry out this analysis and we look forward to submitting pilot batches to PANVAC.
 Regards,

Jeff Mariner

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