European Pharmacopoeia biological reference preparation for poliomyelitis vaccine (inactivated): collaborative study for the establishment of batch No. 3

Inactivated poliomyelitis vaccines are an important part of the World Health Organization (WHO) control strategy to eradicate poliomyelitis. Requirements for the quality control of poliomyelitis vaccines (inactivated) include the use of an in vitro D antigen quantification assay for potency determination on the final lot as outlined in the European Pharmacopoeia (Ph. Eur.) monograph 0214. Performance of this assay requires a reference preparation calibrated in International Units (IU). A Ph. Eur. biological reference preparation (BRP) for poliomyelitis vaccine (inactivated) calibrated in IU has been established for this purpose. Due to the dwindling stocks of batch 2 of the BRP a collaborative study was run as part of the European Directorate for the Quality of Medicines & HealthCare (EDQM) Biological Standardisation Programme to establish BRP batch 3 (BRP3). Twelve laboratories including Official Medicines Control Laboratories (OMCLs) and manufacturers participated. The candidate BRP3 (cBRP3) was from the same source and had the same characteristics as BRP batch 2 (BRP2). During the study the candidate was calibrated against the 3^rd International Standard for inactivated poliomyelitis vaccine using in-house D antigen ELISA assays in line with the Ph. Eur. monograph 0214. The candidate was also compared to BRP2 to evaluate the continuity. Based on the results of the study, values of 320 DU/mL, 78 DU/mL and 288 DU/mL (D antigen units/mL) (IU) for poliovirus type 1, 2 and 3 respectively were assigned to the candidate. In June 2016, the Ph. Eur. Commission adopted the material as Ph. Eur. BRP for poliomyelitis vaccine (inactivated) batch 3.

Regulation and standardization of IPV and IPV combination vaccines

Inactivated poliovirus vaccine (IPV) is not only increasingly used on a global basis but also is a component of many combination vaccines. Standardization and control of IPV continues to be a challenge for manufacturers and regulators. A rat immunogenicity assay is currently recommended by many authorities, including WHO, as the definitive in vivo potency. Alternative in vitro assays to determine D-antigen content have been developed and are routinely used in some countries to assess IPV potency assay. However, the other less reliable in vivo immunogenicity assays are also used (e.g. monkey, chick). We review some of the regulatory challenges facing current and future IPV assessment, with a focus on the relevance of in vivo and in vitro tests, considerations for Sabin derived IPV and discussion of future efforts for standardization.

Diphtheria-tetanus-pertussis (DTP) combination vaccines and evaluation of pertussis immune responses

Diphtheria-tetanus-pertussis (DTP) combination vaccines based on inactivated whole-cell Bordetella pertussis (DTPw) or purified acellular pertussis components (DTPa) facilitate vaccine administration and will allow further co-administration such as with pneumococcal conjugates. Safety and immunogenicity studies are needed to demonstrate non-inferiority between combinations and the separate vaccines. The immunological non-inferiority is based on threshold antibody levels that represent correlates of protection. However, in case of pertussis, correlates of protection have not been defined or accepted. We describe the clinical evaluation of DTPa- and DTPw-based combinations and demonstrate their immunological non-inferiority as compared to their separately administered licensed counterparts. With respect to antibody responses against pertussis, a number of evaluations (vaccine response rates and geometric mean concentrations (GMCs) for anti-PT, anti-FHA, anti-PRN or anti-BPT; reverse cumulative distribution curves) are described. We also demonstrate that the B. pertussis mouse lung clearance model is able to predict clinical efficacy of licensed DTPa and DTPw vaccines and represents a useful tool to evaluate new combination vaccines.

Establishment of European Pharmacopoeia BRP batch 2 for inactivated poliomyelitis vaccine for in vitro D antigen assay

A collaborative study was initiated by the European Directorate for the Quality of Medicines (EDQM) to assign a potency value for the candidate Ph Eur BRP batch 2 against the 2nd International Standard (IS) in order to replace the dwindling stocks of Ph Eur BRP batch 1. The candidate material is a concentrated trivalent bulk (Type 1 (Mahoney), Type 2 (MEF1) and Type 3 (SAUKETT)) from a commercially available IPV vaccine. Nine laboratories participated in the collaborative study. Eight laboratories reported results. Participants performed in-house ELISA assays on the candidate BRP, the 2nd International Standard (IS) and the current BRP (BRP batch 1). An additional sample was included to acquire information on the correlation between the in vitro and in vivo assays based on comparison with a previous study. Results of that comparison are included as an annex. Potency estimates were satisfactory in terms of repeatability and reproducibility, however the estimates for the 2nd IS were significantly lower than those for Ph Eur BRP batch 1. These two reference standards are derived from the same material and were originally assigned the same potency value after a joint study run by EDQM and the WHO in 1994. A reconciliation study was therefore designed to determine if the IS stored at NIBSC and the IS which had been sent from NIBSC to EDQM for use in the initial study were equivalent. 3 of the laboratories from the initial study participated. Results revealed no significant difference between the 2nd IS stocks stored in the two different locations at NIBSC nor between BRP batch 1 and the standards stored at NIBSC for types 1 and 2. For type 3 the 2nd IS standards stored at NIBSC are 13 % less potent than the Ph Eur BRP batch 1. The 2nd IS which had been shipped from NIBSC to EDQM was significantly less potent than BRP batch 1 and the 2nd ISs stored at NIBSC for all three types, confirming the observation of the initial study. Possible explanations for this apparent loss of potency of the 2nd IS used in the study are under investigation. Since Ph Eur BRP batch 1 and the 2nd IS in stock at NIBSC appear no more different than when their original potency assignment was made at their establishment, and since the 2nd IS standard used in the initial part of this study was compromised, a consensus potency value for the candidate BRP was determined using Ph Eur BRP batch 1 as the reference standard. The candidate material was therefore assigned a potency of 320-67-282 D Antigen units/ml (IU) for types 1, 2 and 3 respectively. A stability monitoring program will be initiated. The candidate material was adopted by the European Pharmacopoeia Commission at its session in March 2003 as European Pharmacopoeia IPV vaccine BRP batch 2 for D Ag in vitro assay.

Analysis of an in vivo assay for inactivated polio vaccine

Approaches to the statistical analysis of data from the rat bioassay for Inactivated Polio Vaccine are discussed and compared, using data from a recent collaborative study The measured response, an antibody titre obtained from a doubling dilution series, did not satisfy the requirements of normality and homogeneity of variance necessary for the standard parallel line model for quantitative data. Laboratory-specific cut-offs can be defined, to reduce the data to "positive" or "negative" responses, allowing valid analysis with the probit method.

WHO Expert Committee on Biological Standardization

This report presents the recommendations of a WHO Expert Committee commissioned to coordinate activities leading to the adoption of international recommendations for the production and quality control of vaccines and other biologicals and the establishment of international biological reference materials. The report starts with a discussion of general issues brought to the attention of the Committee and provides information on issues relevant to international guidelines, recommendations and other matters related to the manufacture and quality control of biologicals. This is followed by information on the status and development of reference materials for bovine spongiform encephalopathy, various antigens, blood products, cytokines, growth factors and endocrinological substances. The second part of the report, of particular interest to manufacturers and national control authorities, contains sets of recommendations for the production and control of poliomyelitis vaccine (oral) and poliomyelitis vaccine (inactivated) and guidelines for the production and control of live attenuated Japanese encephalitis vaccine. Also included are lists of recommendations and guidelines for biological substances used in medicine, and other relevant documents.

[Performance of vaccinations against poliomyelitis in the province of Kraków versus the plan of elimination and eradication of this disease in Poland]

The criteria of elimination and eradication of poliomyelitis set down by the WHO and the performance of vaccinations are presented in the Province of Cracow and are compared with the plan of the National Programme of Elimination and Eradication of Poliomyelitis. The analysed period covered the years 1991-1998. In 1998 the World Health Congress passed the resolution on the elimination and eradication of poliomyelitis worldwide. For accepting eradication achieved the criterion is required of vaccination of 90-95% of babies aged under 2 years in the whole country, and not less than 90% in individual provinces. In early 1990's below 75% babies in that age group were vaccinated in the Province of Cracow. Only in 1998 for the first time the 92% rate of vaccinations as required by the WHO was achieved.

CBER: new approaches to biological product testing

Biological products are complex molecules and their testing presents unique technical challenges. Furthermore, there are certain expectations for the validation of methods applied for regulatory purposes. A few recent CBER policy initiatives which have an impact on the use of animal tests for biological products will be discussed, followed by an exposé of the MAPREC test for polio virus neurovirulence as an example of alternative test development and the validation process. Finally, some general comments about the validation process will be made.

A new WHO International Reference Reagent for use in potency assays of inactivated poliomyelitis vaccine

Assays of the potency of inactivated poliovirus vaccine require the use of an appropriate reference reagent. Preparation 91/574 was shown by international collaborative study to be suitable for determination of antigenic content and immunogenicity of inactivated poliovirus vaccines by in vitro and in vivo assays, respectively. The reagent is a trivalent blend of formaldehyde-inactivated monovalent pools of poliovirus type 1 (Mahoney) poliovirus type 2 (MEF-1) and poliovirus type 3 (Saukett). Studies by antigen-capture ELISA showed that the component monovalent pools contained high titres of D antigen and trace amounts of C antigen. Sucrose gradient analysis showed that the D antigenicity was almost exclusively associated with 150S virus particles. Low levels of procapsids (75S particles with D antigenicity) were detected in the type 1 and 2 monovalent pools. The profile of intact virions and procapsids in 91/574 in sucrose gradients was very similar to PU78-02, a previously used inactivated trivalent poliovirus vaccine reference. The World Health Organization (WHO) Expert Committee on Biological Standardization at its 1994 meeting established preparation 91/574 as the 2nd WHO international Reference Reagent for poliomyelitis vaccine (inactivated). A potency of 430, 95, 285 D antigen units per ml was assigned to poliovirus type 1, 2 and 3, respectively. A separate aliquot of this preparation, established by the European Pharmacopeia Commission as a Biological Reference Preparation, has an identical assigned titre. The 2nd WHO International Reference Reagent 91/574 is intended for calibration of secondary reference reagents.

Inactivated poliovirus vaccine: past and present experience

Many countries have made use of inactivated poliovirus vaccine (IPV) in their national poliovirus control programs since 1955. Until 1961 IPV was the only vaccine available for the control of poliovirus, but subsequently many countries opted to use the Sabin attenuated poliovirus vaccine (OPV), which was perceived as more effective in preventing intestinal infection and in ensuring community protection by spreading to unvaccinated contacts of vaccinees. Nevertheless, IPV has remained the vaccine of choice in several countries, where experience has shown that it represents a safe and effective option for disease control. IPV limits subsequent infection of the pharynx and intestine in vaccinees, and is able to control circulation of poliovirus in a vaccinated population, providing effective community protection. Furthermore IPV contains only killed virus and cannot cause vaccine-associated paralytic poliomyelitis as OPV sometimes does. This paper reviews the history of the use of IPV, with emphasis on its efficacy and its ability to safely protect communities in which it is used. As the incidence of poliomyelitis declines new control strategies should take account of the knowledge of the use of poliovirus vaccines acquired since 1955.

A WHO collaborative study of immunogenicity assays of inactivated poliovirus vaccines

Ten laboratories studied the immunogenicity of six trivalent inactivated poliovirus vaccines in a WHO Collaborative Study. The antigenic content of all six vaccines had previously been estimated in an earlier study (Wood et al., 1995). In collaboration with the European Pharmacopoeia Commission an additional preparation, European Pharmacopoeia Biological Reference Preparation Batch 1, was also included. Laboratories were requested to use established immunogenicity assays and six used the European Pharmocoepia guinea pig/chick test while three used a rat potency test. One laboratory contributed data from both methods. Apart from one laboratory, within laboratory variation was low (less than five-fold). However, very large (greater than 100-fold) variation was seen between laboratories for ED50 results in the guinea pig/chick test. Different decisions on pass/fail outcome would have occurred for some of the samples tested. Between laboratory variation was much lower (less than five-fold) in the rat test. Expression of results as potencies relative to a standard reduced between laboratory variation for both methods, substantially so for the guinea pig/chick test. The correlation between in vivo and in vitro results was generally good with the exception of the type 3 component of one preparation. This showed that the relationship between immunogenicity and antigenicity was not necessarily predictable. There is an urgent need to revise the European Pharmocoepia immunogenicity test but it is premature, on the basis of this study, to recommend either the rat test or in vitro tests as replacements. Two candidate reference materials were both found suitable for in vivo assay of inactivated poliovirus vaccine.

[Polio vaccination today: critical remarks]

Vaccination against poliomyelitis remains an absolutely mandatory measure to prevent resurgence of this dreadful viral infection. Today, however, when the chance to get infected is extremely low, one has to reconsider much more the inherent risk of such a living vaccine which is principally able to induce neurologic disease especially in immunocompromised host the number of which is increasing in our population. Since these attenuated vaccine strains multiply largely in the orointestinal tract of a vaccine, those viruses are shed and easily spread into surroundings so that other persons which are not aware of this event are exposed. But also in normal hosts the vaccine strains are able to produce disease because the genetic mutation leading to reduced virulence is not absolutely stable. Back mutations with increased virulence develop during multiplication in the vaccinee and may threaten the vaccinee as well as contact persons. For the sake of security these consequences should be respected much more. Since a dead vaccine of polioviruses is available, one should much more often profit from this choice.

Deleterious effect of thimerosal on the potency of inactivated poliovirus vaccine

High-potency inactivated poliovirus vaccine (eIPV) was combined with diphtheria-tetanus-pertussis (DTP) vaccine containing thimerosal as a preservative to simulate the performance of a potential tetravalent vaccine. Neither type 1 nor type 3 poliovirus antigens appeared to be affected by thimerosal after exposure for 1 h at 37 degrees C as measured by enzyme-linked immunosorbent assay (ELISA). One epitope on the type 2 antigen was damaged within 5 min of exposure; however, the overall potency was unchanged when measured using a polyclonal antibody preparation. Exposure to thimerosal at 37 degrees C decreased the potency of all three poliovirus types to well below the level caused by heat deterioration alone in 1-2 days and to 0% after 16-17 days. At 25 degrees C, the potency of type 1 poliovirus decreased by 46% in 1 day, whereas poliovirus types 2 and 3 were stable for 1 week. Storage of eIPV at 4 degrees C in the presence of thimerosal reduced the potency of type 1 poliovirus antigen to undetectable levels after 4-6 months. Type 2 and 3 antigens were less markedly affected by 8 months of exposure to thimerosal at 4 degrees C. The loss of potency of type 1 as measured by ELISA was paralleled by a reduced level of neutralizing antibodies in mice injected with these preparations. The results obtained from testing eIPV in combination with DTP and thimerosal were generally similar to those obtained using eIPV with thimerosal. It remains to be seen to what extent thimerosal will affect the immunogenicity of eIPV in humans when injected as combined eIPV-DTP vaccine.

Swedish inactivated polio vaccine: laboratory standardization and clinical experience over a 30-year period

Swedish inactivated polio vaccines have contained per single human dose a mean amount of viral antigen equivalent to 1 x 10(7.5) CCID50 of type 1, 1 x 10(7.4) of type 2 and 1 x 10(7.8) of type 3 produced on primary monkey kidney cells. Potency tests were made in comparison with an equivalent amount of live virus suspension of all three types. Validation of tests has been based on the response to type 1 only. Based on clinical experience with vaccine lots from 1957 and the establishment of the second live reference virus suspension in 1966, the minimum limit of immune response in guinea-pigs--expressed in extinction values--was decided as 1.5 for type 1 and type 3, and 1.0 for type 2. The potency test method used since 1959 in Sweden was two subcutaneous injections 2 weeks apart using 10 guinea-pigs per dilution and blood collected 1 week thereafter. Potency tests made according to European Pharmacopoeia revealed a somewhat lower value for type 2. D-antigen content in Swedish vaccines was low, however, the Swedish vaccine has protected against many episodes or outbreaks of wild virus in Sweden and immunized individuals elsewhere in the world. For the Swedish population a clear-cut clinical motivation for requiring a higher potency for type 2 as required in the European Pharmacopoeia or increased levels of D-antigen in the final product has not been presented. It was concluded that the European Pharmacopoeia method did not distinguish between doses of 0.5-1.0 ml. The minimum limit extinction value for type 2, i.e. 2.0 seemed to high.(ABSTRACT TRUNCATED AT 250 WORDS)

Monitoring impact of oral poliovirus vaccine on poliomyelitis trends from physiotherapy records, Ilorin, Nigeria, 1981-1988

During the eight years of a poliomyelitis control programme in Ilorin Local Government Area, Nigeria, 85% of children aged 12-23 months were estimated to have received three doses of trivalent oral polio vaccine. The estimated incidence of paralytic poliomyelitis decreased by 59%, indicating a low vaccine efficacy for the currently used TOPV. This has a serious implication for the World Health Organization's global poliomyelitis eradication strategy of immunizing at least 80% of children aged one year by the year 2000, that eradication may not be achieved by this strategy alone in tropical Africa. Supplementary strategies of mass OPV campaigns, combined IPV/OPV vaccine regimens, or the introduction of new generation of poliomyelitis vaccines may be needed. Similar low-cost efforts at documenting the impact of TOPV on the incidence of poliomyelitis using physiotherapy clinics as independent sentinels, are needed from other states of Nigeria. To increase the efficacy of the primary series of TOPV in Nigeria, the number of doses constituting the primary series should be increased to four (including one at birth). There is now reason to consider a properly timed combination of both IPV and OPV in Nigeria.

Effect of prior immunity on the shedding of virulent revertant virus in feces after oral immunization with live attenuated poliovirus vaccines

Groups of infants were immunized with one or two doses of orally inoculated live attenuated Sabin poliovirus vaccine (OPV group) or with one or two doses of enhanced-potency inactivated poliovirus vaccine (EIPV) administered parenterally followed by one or two doses of OPV (EIPV-OPV group). The fecal specimens from both groups were tested for poliovirus shedding 1-2 months after OPV. The virus isolates were examined for nucleic acid sequences in the 5' noncoding regions (bases 480, 481, and 472 for serotypes 1, 2, and 3, respectively) to determine whether the viruses shed represented nonattenuated revertants, attenuated parent vaccine strains (nonrevertants), or both. In the OPV group, 4 of the 6 virus isolates recovered 30-60 days after the first immunization dose and 1 of the 3 isolates obtained after the second dose were found to be nonrevertants (parent vaccine strain). In contrast, 11 of the 12 isolates in the EIPV-OPV group were of the nonvaccine revertant virus types. The frequency for reversion appeared to differ for different poliovirus serotypes. However, all revertant type 3 isolates were recovered from subjects previously immunized with EIPV.

How to predict the immune status of poliovirus vaccinees? A comparison of virus neutralization at a very low serum dilution versus ELISA in a cohort of infants

A cohort of children from Gaza was observed from birth to the age of one year. Blood specimens were collected at birth, before and after poliovirus vaccination and at one year of age. Poliovirus immunity before and after vaccination was assessed by ELISA and virus neutralization (NT). Positive predictive values for ELISA were between 81.5% and 90.8%. However, ELISA revealed a high frequency of false negatives, and unacceptably low negative predictive values between 28.6% and 55.4%. The history of poliovirus immunity in the cohort was further investigated by NT. A high level of seropositivity to poliovirus type 1 (PV-1) was found. In cord blood, 83.3% had a NT titre greater than or equal to 4 and 99.0% had a titre greater than or equal to 2. Similarly, by one year of age, 85.7% had a titre greater than or equal to 4 and 90.5% had a titre greater than or equal to 2. Seropositivity to PV-2 and PV-3 were slightly lower, ie 80.8% of children had a PV-2 titre greater than or equal to 4 and 75.4% had a PV-3 titre greater than or equal to 4. As for other developing areas, poliomyelitis eradication in Gaza will come about when universal vaccination fills all 'immunity gaps' and improved sanitation and housing reduces the endemicity of wild polioviruses.

Feasible improvements in vaccines in the Expanded Programme on Immunization

Feasible improvements in existing vaccines of the Expanded Programme on Immunization are reviewed. The toxicity of pertussis vaccines can probably be reduced and the immunogenicity increased by recently instituted improvements in purity and selectivity. Candidate vaccines containing inactivated pertussis toxin, with or without other components, are in use in Japan and in controlled trials elsewhere. Inactivated poliovirus vaccines have been improved over the past decade and presently show promise of inducing immunity with as few as two doses administered in infancy. At the same time, improved methods for delivering the oral poliovirus vaccine through mass vaccination campaigns are being increasingly employed throughout the developing world. Major improvements in the measles vaccine will probably come from the development of new stabilizers and the use of vaccines that are immunogenic in the presence of maternal antibody.

Clinical efficacy of a new, enhanced-potency, inactivated poliovirus vaccine

The 1986-87 outbreak of paralytic poliomyelitis in Senegal, with 676 reported cases, provided an opportunity to evaluate the efficacy of an enhanced-potency inactivated poliovirus vaccine (N-IPV) in the Kolda region, where this vaccine has been used since 1980. 89 cases, confirmed to have poliomyelitis with residual paralysis, were enrolled in a case-control study, up to 5 matched controls being obtained for each case. The clinical efficacy for one dose of N-IPV was 36% (95% confidence interval 0%, 67%) and for two doses was 89% (95% CI 62%, 97%).

[Test of the potency of trivalent oral polio vaccines: comparison of 2 methods of reading]

Trivalent oral poliovaccine is used in Argentina to prevent poliomyelitis. Its potency is tested by infectivity titration of the three viruses in susceptible cell cultures (Hep-2 cell line). In order to compare the conventional reading method of cytopathic effect (CPE) with the staining technique of cell monolayers with crystal violet-formol, the reference viruses and several lots of trivalent vaccines were titrated. Between 3 and 10 days post-infection (pi) the plates were read under microscope and immediately stained. The maximum viral titer was reached at 5-7 days pi and additional CPE after this period did not alter the results. An incomplete monolayer confluence or cell aging (6-7 days pi) resulted in a poor definition between positive and negative cultures when the staining test was used. By contrast, CPE was easily read by microscope observation. Therefore, the staining method should only be considered for vaccine titration as a possible alternative when an inverted microscope is lacking or a great number of plates has to be read. In this case, to stain at day 7 pi is recommended.

Sera collected before introduction of contaminated polio vaccine contain antibodies against SV40

Anti-SV40 IgG antibodies were found by ELISA test in 6 out of 51 sera collected in 1952, i.e. before introduction of the polio vaccine. This indicates that the presence of SV40 in the human population whose footprints can be found in a fraction of human cerebral tumours need not be the consequence of contamination of early batches of polio vaccine with SV40.

The standardization of infectivity titrations of poliovaccines--a WHO collaborative study

The reproducibility of a method for infectivity titrations of live poliovaccines using microtitre plates was investigated in a WHO collaborative study involving eight laboratories. The large variation (up to 100-fold) in estimates of infectivity observed between laboratories using their local methods of assay was reduced to no more than fourfold when a common method was used. However, expressing infectivities relative to those of the monovalent reference viruses improved the agreement between the laboratories irrespective of the titration method employed. On the basis of these results, WHO adopted the common method used in the study as its recommended method for poliovirus titrations and established the preparations studied as international reference materials for the infectivity titrations of live poliovaccines.

Induction of long-term immunity to paralytic poliomyelitis by use of non-infectious vaccine

Naturally acquired immunity to paralytic poliomyelitis, which is of long duration, is associated with serum antibody, immunological memory, or both. Persistence of circulating antibody is reassuring but not essential for long-term protection. Immunological memory induced by killed poliovirus vaccine is similar to that induced by infection, which is not a prerequisite for the induction of long-term immunity. Animal studies of experimental vaccines indicate that some antigenic components of poliovirus induce immunological memory without producing detectable antibody; killed poliovirus vaccine has the same effect in man. Killed vaccine containing 40, 8, and 32 D-antigen units of poliovirus types 1, 2, and 3, respectively, protects all recipients in both one-dose and two-dose schedules. This means that either schedule can be chosen to fit in with local immunisation programmes and thus reduce costs and increase population coverage.

Current advances in viral diagnostic technology applicable to polio vaccination and diagnosis

Advancements in the fields of molecular virology, immunology, biochemistry, and physical chemistry have enabled the development of sensitive and specific assays for rapid diagnosis. Similarly, developments in antiviral chemotherapy have provided meaningful incentives. Some of these newly emerging methods have found their way into the laboratories involved in production of poliovirus vaccine, research, and diagnosis. This discussion addresses approaches to standardizing vaccines with these newer techniques.

One-dose immunization against paralytic poliomyelitis using a noninfectious vaccine

Recent advances in production and standardization of noninfectious poliovirus vaccine now make it feasible to induce durable immunity against paralytic poliomyelitis with one dose of a suitably standardized vaccine. A single dose of a vaccine containing 40, 8, and 32 D-antigen units of type 1, 2, and 3, respectively, administered to six-month-old infants, was observed to induce antibody levels of greater than or equal to 1:4 in greater than 90% and immunologic memory in all. Since protection against paralysis is associated with the presence of either type-specific serum antibody or type-specific immunologic memory, and since immunologic memory once induced is irreversible, then lifelong immunity to paralytic poliomyelitis can be induced with a single dose of a suitably standardized vaccine administered at five to seven months of age. In areas of the world where exposure to poliovirus can occur before this age, vaccine should be administered earlier. Until the influence of age and/or maternal antibody has been further studied, infants immunized before the age of six months should receive a second dose after six months of age.

The standardization of vaccines: a discussion

Many changes have been made in the World Health Organization's (WHO) requirements for the production and control of both the killed and live (oral) poliovirus vaccines since their initial formulations in 1959 and 1962, respectively. The major changes in the production of killed vaccine concern the cell substrates used from primary tissue to passaged primary tissue or even a continuous cell line such as Vero. It has been shown also that there is no longer the necessity to test for residual infectious virus by the inoculation of monkeys, since cell cultures are much more sensitive for this purpose. For the live vaccine, a more uniform test for the titration of virus content has been introduced. Furthermore, international agreement on the details of the test for neurovirulence in monkeys has been reached. The expression of the immunogen of poliovirus in eukaryotic cells has been achieved, but whether it becomes a commercial proposition replacing one or both of our present vaccines remains to be seen.

Inactivated poliovirus vaccine: current production methods and new developments

The biotechnologic developments during the last decade have led to the production of inactivated poliovirus vaccine (IPV) on an industrial scale and at economically acceptable costs. Replacement of primary monkey kidney cells by subcultured monkey kidney, Vero, or human diploid cells as substrate for virus multiplication as well as the introduction of the microcarrier culture technique have made cell and virus cultivation in large fermentors of 100-1,000 liters feasible. Procedures for processing virus harvests into highly concentrated purified vaccines were developed; also, the safety and potency control tests were improved and simplified. It has been demonstrated that these more potent poliovirus vaccines, either alone or in combination with diphtheria-tetanus-pertussis vaccine, induce a high immunity with reduced vaccination schedules. The overall costs of vaccination will be reduced considerably in this way. In addition, the results of biochemical and immunologic studies indicate that neutralizing antibodies can be induced by the viral proteins alone. These findings open up promising perspectives for production of subunit poliovirus vaccines with use of recombinant DNA and synthetic antigen, a method that has already proved feasible for producing vaccine against foot and mouth disease. These new techniques may lead to a further reduction of production costs and will improve the safety of the vaccine.

Inactivated poliovirus vaccine and test development at Connaught Laboratories Ltd

Trivalent inactivated poliovirus vaccine (IPV) (MK) was made, purified, and inactivated according to the amended Rijks Instituut (The Netherlands) protocol from primary monkey kidney tissue grown on microcarrier cultures. Losses of the type 2 component due to adsorption to the glass ampule occurred with the purified vaccine preparation. This problem was solved by changing the diluent, and the vaccine was submitted for evaluation in clinical trials at Johns Hopkins (Baltimore, Md.). Phase 2 of the development was to standardize production of IPV from MRC-5 (human diploid) cells on microcarriers and otherwise follow the Rijks Instituut 's method. Results of experimental trivalent vaccine production and testing showed that the number of effective doses harvested from MRC-5 cell cultures compared favorably with vaccine derived from monkey kidney. The yields could be further increased with stearyl tyrosine as adjuvant. Large-scale production using 200-liter fermenters is in progress. Poliovirus particles of various densities in cesium chloride can be found in any IPV preparation and give rise to different immunogenic responses. As shown in this paper, some of these virus fractions produce a low primary humoral antibody response but appear to be important for memory induction.

Killed poliovaccine: an evaluation of safety testing

Several important changes in the production process of killed poliovaccine have recently taken place or are taking place concerning cell substrate as well as production techniques. Some of the consequences of these changes for the safety testing of the vaccine will be briefly discussed. Data will be presented to show that tests in tissue culture are more sensitive than those in monkeys for the detection of residual live poliovirus in vaccine. It is concluded that there is no need for an additional test in monkeys when tests in tissue culture are carried out according to W.H.O. requirements.