Laboratory testing of whole cell pertussis vaccine: a WHO proficiency study using the Kendrick test

Whole cell pertussis vaccine (WCV), commonly in combination with vaccines f or diphtheria and tetanus, has an important role in reducing morbidity and mortality among children in most parts of the world. Testing to assure the efficacy of such vaccines is essential. We have, therefore, carried out, un der the Global Training Network (GTN) of the Department of Vaccines and Bio logicals at the World Health Organization (WHO), a proficiency study involv ing 13 laboratories in 12 countries that routinely test WCV. Two vaccine sa mples were tested in this study and represented samples which were expected clearly either to pass (sample B, a full strength vaccine) or to fail (sam ple A, 1/8 strength of vaccine B). Data from this study showed good perform ance by the majority of participants. Most assays were statistically valid and were carried out to the level of precision achieved for these assays in previous studies. This study also indicated that, relative to the assay pr ecision. the in-house reference (IHR) preparations are in general accuratel y calibrated. Statistically valid assays of the sub-potent vaccine, A, show ed it to fail in all except one laboratory. Statistically valid assays of t he potent vaccine. B, showed it to pass in al I laboratories. Nevertheless, the between laboratory variability of estimates for vaccine B, and for com parisons of the two vaccine samples suggested that there are some differenc es in results in different laboratories. The introduction of a common worki ng standard may assist in reducing inter-laboratory variation. This study h as shown clearly satisfactory performance by most laboratories. However, a serious problem was detected in one laboratory where the sub-potent vaccine A could have been passed and was not distinguished from the eight-fold mor e potent vaccine B. There were also indications of possible problems in sev eral other laboratories. where IHR preparation may not be accurately calibr ated or where vaccine samples A and B may not be completely distinguished. Although this study provides reassurance that most laboratories perform wel l, it demonstrates the essential role of ongoing proficiency studies in hig h-lighting problems. (C) 2001 Elsevier Science Ltd. All rights reserved.