Potency testing of diphtheria and tetanus toxoids. A reliable, pragmatic and economic approach.

The aim of potency testing is to ensure that vaccines under test will provide protection when used in human subjects. To achieve this, many potency tests for diphtheria and tetanus toxoids have been devised. the potency tests listed in the European Pharmacopoeia and the W.H.O. Requirements call for the use of large numbers of either guinea pigs or mice. These quantal assays are extremely expensive to perform and alternative, more economic methods are clearly needed. The results presented here illustrate that, provided certain rules are followed single point assays can provide the same degree of assurance of potency as the three-point assays currently in use.

Mumps vaccine L-Zagreb, prepared in chick fibroblasts. I. Production and field trials.

Leningrad-L3 Mumps Vaccine virus has been further attenuated by adaptation and passage on SPF chick embryo fibroblast cell cultures. This new mumps strain has been designated L-Zagreb and has been used to prepare mumps vaccines which meet the WHO requirements. Observations during both the field trial period prior to registration and during the later use of the vaccine showed that the few reactions observed were mild and that seroconversion was obtained in 88-98% of vaccines. The morbidity of mumps in Croatia declined more than tenfold after the introduction of the new vaccine. During a mumps epidemic, vaccine efficiency was calculated to be 97-100%.

A tissue culture assay for diphtheria toxicity testing.

A tissue culture assay system in microtitre plates using a Vero cell line has been compared with the traditional guinea pig skin reaction test to detect residual toxicity during the diphtheria toxin detoxification procedure. A standard batch of untreated diphtheria toxin was used as a reference standard in each of the assays. The tissue culture assay proved to be sensitive, specific, economical and reproducible and offers an alternative to the use of guinea pigs in testing for any residual toxicity in diphtheria toxoid samples.

Stability of BCG vaccines.

Connaught freeze-dried BCG vaccine is distributed in amber vials sealed with grey butyl rubber stoppers. This report gives data showing the stability of BCG vaccine in this presentation at 4 degrees C and 37 degrees C, for 1, 10, 20 and 50 dose vials. The results demonstrate that BCG vaccine prepared in vials is a stable product and could be useful in mass-immunization campaigns.

The immunogenicity of K99 antigen in whole cell bacterins of Escherichia coli.

K99 antigen in Escherichia coli whole cell bacterins was immunogenic in rabbits and mice. Mice vaccinated subcutaneously and bled three weeks later had a serum antibody response which was dose dependent. The dose response on dilution of bacterins was shown to be mainly due to dilution of K99 antigen, rather than the reduction in adjuvant or bacterial cell concentration. The procedure appears to be a satisfactory one for immunogenicity testing of bacterins containing K99 antigen.

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.

Irreversibility of toxoids. An improved method of testing.

Reversion of toxoid to toxin has been described by several authors yet present day regulations of all National Control Authorities have no specific requirements to check for this possibility. Most producers however have included some form of test in their own protocols for release. We have developed a satisfactory test for both diphtheria and tetanus toxoids which involves storing diluted toxoid at 20 degrees C and 34 degrees C for 6 weeks and performing a full toxicity test on the samples. In the case of diphtheria toxoid we have evidence that it may be dangerous to rely on the simpler guinea-pig skin test, since we have shown that several lots, while giving a negative skin reaction, exhibit diphtheria toxicity when given systemically. It is felt that an in vivo conversion to toxin may occur in some lots which would not be detected by the skin test.

Pertussis vaccine--fact and fiction.

The present paper indicates a number of unresolved problems in the metabolism of Bordetella pertussis and in the standardization of pertussis vaccines. The use of chemically defined media should enable the metabolic problems to be clarified. The problems concerned with the control and standardization of vaccines can largely be resolved in the laboratory with the introduction of reference preparations but the question of the reactivity of vaccine remains for the future.