A review of the effectiveness of vaccine potency control testing.

The use of potency control testing is a valuable tool for testing the actual relative strength of manufactured assembly lots of vaccine. Biological-based manufacturing methods are inherently variable and potency testing is a tool to ensure lot-to-lot consistency of commercial vaccines. A strong historical link to clinical efficacy has been established where correlation to efficacy and adequate test validation have been achieved. The link to immunogenicity and efficacy has traditionally been strongest with attenuated vaccines and toxoids. Control potency test failure does predict that a serial or batch of vaccine would most likely provide insufficient immunogenicity in typical field applications. Because of the complexity of pathogenic processes and associated immune responses, potency tests may not always directly predict the effectiveness of a vaccine. Thus, vaccines that pass control potency testing may not always provide adequate efficacy. This is particularly true of adjuvanted, inactivated vaccines. In the development of vaccine formulations and control tests for vaccines, the nature of the desired protective immune responses to the targeted pathogen (when known) should be considered. These considerations could provide better alternatives in the assays chosen as correlates of immunity and may more accurately predict efficacy and assure batch-to-batch consistency. Also, the effects of the dose and duration of antigen exposure as well as the nature of antigen presentation and generation of extrinsic cytokines could be characterised and correlated to vaccine potency as additional indicators of vaccine efficacy.

Protective effect of Clostridium septicum alpha-toxoid vaccine against challenge with spores in guinea pigs.

The protective effect of an alpha-toxoid vaccine of Clostridium septicum purified alpha-toxin was investigated in guinea pigs. Purified alpha-toxin was treated with formalin to make toxoid, and alpha-toxoid vaccine was prepared by mixing alpha-toxoid (4 to 64 microg/dose) with an aluminum phosphate gel as adjuvant. Guinea pigs were immunized twice with different doses of alpha-toxoid vaccine, and challenged with spores of C. septicum. The guinea pigs surviving after challenge had been immunized with 8 microg/dose or more of alpha-toxoid. All these animals produced titers of 20 units or higher of antitoxin at the challenge. The results suggest that C. septicum alpha-toxin plays an important role in protection against challenge with spores in guinea pigs.

An in vitro approach in quality control of toxoid vaccines.

For routine immunogenicity testing of traditionally produced vaccines, animal tests are required by regulatory authorities, with potency estimated in International Units. A new concept focuses on assuring immunogenicity by monitoring batch-to-batch consistency in production. This concept is used for well-defined biologicals such as hormones. Through the use of immunochemical and bio- and physiochemical techniques the traditional products can be characterised as completely as possible. Developments in in vitro methodologies offer opportunities for immunogenicity testing in vitro. This study describes the possibilities for applying the consistency concept to the traditional products, tetanus and diphtheria toxoids. The sources of variation in these products were studied by flocculation time, SDS-PAGE, biosensor analysis, gel permeation chromatography and in vitro cytokine production studies. Batch-to-batch variation was shown using these in vitro techniques. Results indicate that it is possible to apply the consistency concept in the quality control of traditional vaccines like tetanus and diphtheria toxoids.

Opportunities to reduce the use of animals in the potency and toxicity testing of toxoid vaccines.

Alternative methods for titrating antitoxin are now available which should, in principle, permit a very large reduction in the numbers of animals required to test the potency of toxoid vaccines. More importantly they make it possible to eliminate the use of animals for the indication of excess toxicity almost completely. The full realisation of this potential is dependent upon the careful validation of all other methods and the introduction of more appropriate standard and reference preparations for titration of antisera and for the assay of DTP. It would be facilitated by a mechanism to facilitate the wider dissemination of relevant monoclonal antibodies and by a restructuring of veterinary vaccine potency tests to make full use of the additional serological information provided by the new methods.

General recommendations on immunization. Recommendations of the Advisory Committee on Immunization Practices (ACIP).

This revision of the General Recommendations on Immunization updates the 1989 statement. Changes in the immunization schedule for infants and children include recommendations that the third dose of oral polio vaccine be administered routinely at 6 months of age rather than at age 15 months and that measles-mumps-rubella vaccine be administered routinely to all children at 12-15 months of age. Other updated or new sections include a) a listing of vaccines and other immunobiologics available in the United States by type and recommended routes, advice on the proper storage and handling of immunobiologics, a section on the recommended routes for administration of vaccines, and discussion of the use of jet injectors; b) revisions in the guidelines for spacing administration of immune globulin preparations and live virus vaccines, a discussion of vaccine interactions and recommendations for the simultaneous administration of multiple vaccines, a section on the interchangeability of vaccines from different manufacturers, and a discussion of hypersensitivity to vaccine components; c) a discussion of vaccination during pregnancy, a section on breast-feeding and vaccination, recommendations for the vaccination of premature infants, and updated schedules for immunizing infants and children (including recommendations for the use of Haemophilus influenzae type b conjugate vaccines); d) sections on the immunization of hemophiliacs and immunocompromised persons; e) discussion of the Standards for Pediatric Immunization Practices (including a new table of contraindications and precautions to vaccination), information on the National Vaccine Injury Compensation Program, the Vaccine Adverse Events Reporting System, and Vaccine Information Pamphlets; and f) guidelines for vaccinating persons without documentation of immunization, a section on vaccinations received outside the United States, and a section on reporting of vaccine-preventable diseases. These recommendations are based on information available before publishing and are not comprehensive for each vaccine. The most recent Advisory Committee on Immunization Practices (ACIP) recommendations for each specific vaccine should be consulted for more details.

Immunisation against ovine caseous lymphadenitis: comparison of Corynebacterium pseudotuberculosis vaccines with and without bacterial cells.

Sheep were immunised with Corynebacterium pseudotuberculosis vaccines prepared from cell-free toxoid or from toxoid with formalin-killed cells of C pseudotuberculosis added. Resistance of sheep to infection was tested 6 months after immunisation by inoculation with caseous lymphadenitis pus. The outcome was assessed 3 months later by slaughter and inspection of the sheep for lesions of caseous lymphadenitis. immunised sheep were adequately protected against infection as shown by a significant reduction in the number of sheep exhibiting lesions compared with control sheep, and by fewer abscesses in affected vaccinated sheep than in affected control sheep. The protective potency of the vaccines was not improved by the inclusion of cells of C pseudotuberculosis.

[A hemagglutination inhibition test for control of the quality and effectiveness of highly-purified C. chauvoei toxoid vaccine]. / Ein Hämagglutinations-Hemmungstest zur Kontrolle von Qualität und Wirksamkeit hochgereinigter C. chauvoei Toxoid-Vakzine.

To control quality and efficiency of a highly purified C. chauvoei vaccine which has been developed in Göttingen a haemagglutination-inhibition test is presented. Laboratory and field trials did demonstrate the value of the test. Vaccinated guinea pigs which presented positive HIT titers survived the challenge. Cattle, vaccinated with the vaccine in Germany, Madagascar and Mexico showed positive titers which could be boostered through repeated vaccination.

Acellular pertussis vaccines: evaluation of reversion in a nude mouse model.

An animal model has been developed to assess the safety of acellular pertussis vaccines in terms of reversion to toxicity. Adsorbed pertussis toxoid preparations, alone or combined in a DTP formulation, were administered to nude mice intraperitoneally. In parallel, groups of positive and negative control mice received pertussis toxin and buffer, respectively. The circulating white blood cells of the animals were monitored for 28 days. Mice immunized with glutaraldehyde toxoid preparations did not develop a lymphocytosis during the observation period, whereas mice immunized with an experimental formalin pertussis toxoid vaccine exhibited a high lymphocytosis six days after vaccine administration, demonstrating, in this model, a reversion of the toxoid. The nude mouse model thus appears to reveal the in-vivo reversion of pertussis toxoids and could be included in the quality control panel for the assessment of the safety of acellular pertussis vaccine.

Effective immunization of lambs against enterotoxaemia.

In contrast to adult sheep, 2- to 3-month-old lambs do not respond well to a single injection of Clostridium perfringens Type D oil adjuvant epsilon toxoid. This unresponsiveness can be overcome, however, by administering 2 injections of oil adjuvant vaccine or one injection of oil adjuvant followed 4 weeks later by an injection of alum-precipitated toxoid. The latter procedure evokes protective antitoxin levels which persist for 8 months, and a booster injection of alum-precipitated toxoid given at this stage results in an immunity which lasts for at least 1 year.

Development, preparation and safety testing of a Clostridium welchii type C toxoid. I: preliminary observations in man in Papua New Guinea.

The reactogenicity and immunogenicity of various strengths of plain and adsorbed Cl. welchii type C toxoid have been evaluated in laboratory tests and in man in Papua New Guinea. The greater antigenicity and acceptable clinical reactivity of a vaccine containing 50 total combining power units per 0.5 mm of adsorbed toxoid resulted in its selection for further field studies.

Development, preparation and safety testing of a Clostridium welchii type C toxoid. II. Laboratory evaluation of potency.

The results obtained with four laboratory tests on four candidate formulations of Clostridium welchii type C vaccine for use in man have been compared with clinical responses to the same vaccines. Quantal response assays in mice appeared to reflect the ranking of the four vaccines in human subjects better than did the guinea pig tests. They also enabled the potency of the vaccine preparations to be related to an existing International Reference Preparation. Mouse assays in which the animals received two spaced doses of vaccine prior to challenge yielded marginally more satisfactory results in terms of precision and reflection of human responses than did assays involving a single dose of vaccine.

The International Reference Preparations of Clostridium welchii (C. perfringens) beta and epsilon toxoids.

The Central Veterinary Laboratory, Weybridge, England was requested by the WHO Expert Committee on Biological Standardization to obtain suitable materials for international standards for Clostridium welchii (C. perfringens) beta and epsilon toxoids and to arrange collaborative assays. Preparations were obtained and dispensed as freeze-dried toxoids in ampoules. The toxoids were assayed by nine laboratories in eight countries. On the basis of the results obtained, the materials have been established as the International Reference Preparations of Clostridium welchii (C. perfringens) Beta and Epsilon Toxoids.

The stability of bacterial vaccines at elevated temperatures.

The requirements for vaccines demand that they be safe and efficacious. The recommended storage temperature for vaccines is 2-8 degrees C, but their conditions of storage and transportation in the developing countries may frequently be far from ideal. This had led to the present study in which several vaccines have been stored at ambient temperature (+24 degrees C) and at +37 degrees C and their antigenic stabilities examined. Under these adverse conditions, typhoid, cholera and the components of DPT vaccines either in final containers or in bulk form have been shown to be stable for extended periods of time.

[Evaluation of the quality of dry anatoxins in the process of their production]. / Otsenka kachestva sukhikh anatoksinov v protsesse ikh proizvodstva.

On the example of production of botulin toxoids of A, B and E types the authors demon strated the expediency of using the agar gel diffuse precipitation test for preliminary assessment of the toxoid activity, instead of a more expensive and complicated antitoxin-binding test.

[Standardization of chemical cholerogen-toxoid cholera vaccine according to the content of somatic O-antigen]. / Standartizatsiia khimicheskoi kholernoi vaksiny kholerogen-anatoksin po soderzhaniiu somaticheskogo O-antigena

The authors discuss the results of studies on the choice of highly-reproducible and sufficiently informative methods of 9-antigen standardization in a new chemical vaccine against cholera (cholerogen-toxoid); materials were collected under conditions of controlled epidemilogical trial. Titration of O-antigen in industrial batches of the preparation with the aid of precipitation in gel against standard O-cholera serum could be used for its standardization. Quantitative limits of O-antigen responsible for the formation of vibration (antimicrobial) antibodies in the persons vaccinated were found by studying the immunogenicity and reactogenicity of a number of cholerogen-toxoid batches contrast by O-antigen content described by means of the precipitation test.

Clostridium oedematiens: observations on potency assaying.

The United States has established a Standard Requirement for the potency testing of biological products containing Clostridium oedematiens belonging to two types: type B (Cl. novyi) and type D (Cl. haemolyticum). Guinea pig testing has provided widely varying results depending on the origin of the animals. The tests reported are intended to determine the efficacity of the vaccines (Cl. novyi and Cl. haemolyticum) depending on the animal tested: guinea pigs, sheep and bovines; they further establish a parallelism between the antitoxin titer and the immunity of the animal.