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.