WHO informal consultation on the application of molecular methods to assure the quality, safety and efficacy of vaccines, Geneva, Switzerland, 7–8 April 2005

In April 2005, the World Health Organization convened an informal consultation on molecular methods to assure the quality, safety and efficacy of vaccines. The consultation was attended by experts from national regulatory authorities, vaccine industry and academia. Crosscutting issues on the application of molecular methods for a number of vaccines that are currently in use or under development were presented, and specific methods for further collaborative studies were discussed and identified. The main points of recommendation from meeting participants were fourfold: (i) that molecular methods should be encouraged; (ii) that collaborative studies are needed for many methods/applications; (iii) that basic science should be promoted; and (iv) that investment for training, equipment and facilities should be encouraged.

Developments in the production and quality control of poliovirus vaccines – Historical perspectives

Using virus grown in monkey kidney cells, Salk and his colleagues developed an inactivated poliovirus vaccine (IPV) in 1952. A large-scale field trial showed the vaccine to be safe and highly immunogenic in children, but soon after the vaccine became generally available in 1955, cases of paralytic disease were reported in recipients. Investigations showed that almost all the cases occurred in children who had received vaccine from one particular manufacturer. Extensive studies attributed the disaster to problems with inactivation. Addition of a Seitz filtration step midway during formalin inactivation and extension of the inactivation period resulted in a safe vaccine. No further paralytic cases were observed following the use of several hundred million doses of this improved vaccine. Thus, IPV was safe and caused a dramatic decline in the incidence of poliomyelitis in countries where it was used. A second generation IPV is produced in fermentors using well-characterized cell strains or continuous cell lines. The major breakthrough in the development of live poliovirus vaccine was the application of tissue culture methods for virus attenuation. By 1959 several candidate live oral poliovirus vaccines (OPV) had been developed. These were clinically tested in millions of individuals and found to be safe and effective. Since the attenuated virus strains developed by Koprowski and Cox were more neurotropic in monkeys than the Sabin strains, only the latter was licensed in the USA in 1961 and endorsed shortly after by the World Health Organization (WHO). The widespread use of Sabin's OPV in many countries hastened the development of International Requirements by WHO for OPV in 1962 to define the criteria that ensured the uniformity of batches produced by different manufacturers. These have been updated continuously in light of new information and quality control procedures. Extensive field trials have shown the risk of OPV associated polio to be less than 0.3 per million doses administered.

Polio vaccine: The first 50 years and beyond

A conference on "Polio vaccine: the first 50 years and beyond" was held in Toronto, Canada, June 2005. The purpose of the conference was to bring together regulators, manufacturers, academics and public health authorities to celebrate the accomplishments of the past 50 years, to consider the challenges of achieving and sustaining polio eradication and to review standardization and regulatory issues around existing and new polio vaccines. In the final session of the conference the following summary of the meeting was presented.

Polio vaccines, SV40 and human tumours, an update on false positive and false negative results

Simian virus 40 (SV40) has been detected in different human tumours in numerous laboratories. The detection of SV40 in human tumours has been linked to the administration of SV40-contaminated polio vaccines from 1954 until 1963. Many of these reports linked SV40 to human mesothelioma. Some studies have failed to detect SV40 in human tumours and this has caused a controversy. Here we review the current literature. Moreover, we present evidence showing how differences in the sensitivities of methodologies can lead to a very different interpretation of the same study. The same 20 mesothelioma specimens all tested negative, 2/20 tested positive or 7/20 tested positive for SV40 Tag by simply changing the detection method on the same immuno-precipitation/western blot membranes. These results provide a simple explanation for some of the apparent discordant results reported in the literature.

Is there an association between SV40 contaminated polio vaccine and lymphoproliferative disorders? An age-period-cohort analysis on Norwegian data from 1953 to 1997

Between 1955 and 1963, an estimated number of 150 million people in various parts of the world, including Norway, received poliomyelitis vaccine possibly contaminated with infectious simian virus 40 (SV40). Human studies have investigated the hypothesised association between SV40 and various cancers, but the results have so far been contradicting. The aim of the present study was to examine Norwegian cancer incidence data to assess a possible association between birth cohorts assumed to have been subjected to the vaccine and the incidence rate of lymphoproliferative disorders (excluding Hodgkin's lymphoma), further subdivided into non-Hodgkin's lymphoma (NHL), lymphocytic leukemia and plasma cell neoplasms. Between 1953 and 1997, the incidence rate of lymphoproliferative diseases combined increased about 3-fold in both males and females. Subgroup analysis showed that this increase was largely attributable to NHL. Age-period-cohort modelling of the subgroups, as well as of all groups combined, showed that the cohort effect was more prominent than the period effect. However, the variations in incidence patterns across the birth cohorts did not fit with the trends that would be expected if a SV40 contaminated vaccine did play a causative role. Thus, our data do not support the hypothesis of an association between the vaccine and any subgroup of lymphoproliferative diseases.

Feasibility study to develop a common in vitro D antigen assay for inactivated poliomyelitis vaccines

A feasibility study was organised to determine the possibilities for development of a common in vitro assay for determination of D-antigen content in inactivated poliomyelitis vaccines (IPV). 3 different methods were tested on a selection of non-combined IPV vaccines from the European market. The results of this preliminary study suggest that for vaccines with a similar strain composition similar results would be achieved regardless of which of the three methods was used. Nevertheless, for one vaccine with a slightly different strain composition the results obtained depended on which method was applied. This highlights the need to take into account the strain composition in any future development of a common method. The study also highlighted the importance of standardising the statistical approach to analysis of results, since one laboratory obtained different sets of results by applying different statistical analysis to the same raw data. While no immediate need was seen for a large collaborative study to establish a common method, participants encouraged the idea of further study, in particular with respect to the different strain compositions. Adaptation of a common method will also require further analysis of the needs for combined vaccines, including the steps and conditions for de-sorption.

Multiplex PCR method for identifying recombinant vaccine-related polioviruses

The recent discovery of recombinant circulating vaccine-derived poliovirus (recombinant cVDPV) has highlighted the need for enhanced global poliovirus surveillance to assure timely detection of any future cVDPV outbreaks. Six pairs of Sabin strain-specific recombinant primers were designed to permit rapid screening for VDPV recombinants by PCR.

Simian cytomegalovirus and contamination of oral poliovirus vaccines

In the 1950s the use of primary rhesus macaque kidney cultures to propagate poliovirus for vaccine production led to the contamination of vaccines with simian virus 40 (SV40). African green monkey kidney (AGMK) cultures free of SV40 were used as an alternative cell substrate for vaccine manufacture. In this study we evaluate oral poliovirus seeds, vaccine bulks and vaccines themselves for the presence of a common contaminant of AGMK cultures, simian cytomegalovirus (SCMV). Using sensitive polymerase chain reaction (PCR) techniques, nearly half of the samples analysed were found to be contaminated with SCMV sequences. However, vaccine bulks, positive by PCR for SCMV failed to show any evidence of infectious virus in these studies. One poliovirus vaccine and one seed, propagated on rhesus macaque kidney cultures were found to be positive for the rhesus monkey CMV by PCR.

[Vaccine protection of Swedish children. Time for revision of replacing doses of diphtheria, tetanus, polio and pertussis]

The Swedish vaccination programme against diphtheria, tetanus, pertussis, polio and Haemophilus influenzae type b is characterized by few, widely spaced doses. Swedish schoolchildren have low diphtheria antibody levels compared to children in other countries. The introduction of acellular pertussis vaccine in 1996 has markedly cut the pertussis incidence in all ages except school-age children. There are now reasons to consider replacing the present fourth dose of inactivated polio vaccine given at 5 years of age and the diphtheria-tetanus toxoids given at 10 years of age with a combined diphtheria-tetanus-polio-acellular pertussis vaccine dose to be given at 5-6 years of age. A fifth dose of a DTPaPolio vaccine should be considered at 15-18 years of age.