A simplified plaque assay for varicella vaccine.

A simple and accurate plaque assay is described for potency testing of attenuated varicella vaccine. Assays were performed on the African green monkey kidney continuous cell line CV-1, in multidish-plates, under a semi-solid carboxymethylcellulose overlay. The test is economical and yields accurate individual titre estimates, the reliability of which may be assessed by parallel titration of reference preparations.

Production and quality control of the Oka-strain live varicella vaccine.

The Smith Kline-RIT live attenuated Oka-strain varicella vaccine (Varilrix) is manufactured following the seed lot principle, with each vaccine lot derived from the same working seed. Production of the vaccine basically consists in the multiplication of the working seed under standardized, well-defined conditions guaranteeing consistency of the vaccine lots. Quality control tests, determining the vaccine's purity, safety, potency, and efficacy, are carried out at each defined stage of the production process.

Stability of freeze-dried and reconstituted measles vaccines.

The stability of the titer of live vaccines is a very important factor for successful immunization, especially in countries with a hot climate. For the freeze-dried vaccine, the results of stability tests show that the second generation Rimevax possesses the desired resistance to thermodegradation. In the refrigerator, the shelf life is at least 2 years. Exposure at 20--25 degress C for 1 month, at 37 degrees C for 7 to 14 days or at 41 degrees C for 3 to 7 days results in a vaccine retaining its full immunogenic activity. The value of an accelerated stability test at 37 degrees C for 7 days for the prediction of the potency of each lot is proven. This test should be part of the minimum requirements for live vaccines. The potency of reconstituted measles vaccines is evaluated. Rimevax shows a remarkable stability at higher temperatures. At 37 degrees C, the immunogenic activity is retained for 2 to 3 hours. Reconstitution with diluent at 41 degrees C and subsequent exposure to this temperature does not affect the titer significantly during the first half hour. The comparison of published stability data of measles vaccines shows that Rimevax is one of the most thermoresistant preparations.

Stability of live, freeze-dried virus vaccines.

Stability of live, freeze-dried vaccines is a major factor for successful vaccinations. Vaccines may be stored at -20 degrees C or less for long periods without loss of activity and this storage does not affect stability during subsequent storage. Storage in the refrigerator for long periods is harmless for certain very stable vaccines such as influenza, rubella, NDV, Marek's. Other vaccines, such as IBV, show a significant loss in titer after 2 years. The routine use of an accelerated stability test, e.g. exposure of each lot manufactured to 37 degrees C during 7 days, provides useful information regarding the stability of the vaccine at +4 degrees C. In general the loss during the accelerated stability test is higher than the loss after 24 months storage in the refrigerator. Specifications requiring that each vaccine lot must possess, after the accelerated test, a titer equal to or higher than the minimum titer needed for immunization, are a guarantee of sufficient potency at the time of administration. To solve the problems in tropical countries stable vaccines are essential. Cendevax and Rimevax exposed to tropical temperatures still possess the minimum required titer after several days.