A comparative study of reactogenicity and immunogenicity of an oral and an inactivated polio vaccine.

Reactogenicity and immunogenicity of the oral live attenuated (OPV) and inactivated polio vaccines (IPV) were studied in primary vaccination of toddlers. Three doses were administered simultaneously with DPT following the usual schedule valid in Croatia. The two groups of children had about 100 children each. Postvaccinal reactions were recorded for three days after each vaccination, and seroconversion was determined one month after the last injection. Although a conclusive analysis of postvaccinal reactions is not possible, since the staff of four different health centers apparently did not observe the same criteria, vaccination with IPV + DPT was not associated with remarkably more adverse events than OPV + DPT. Seroconversion rates attained with OPV ranged between 95.2% and 99.0%. With IPV, the rates were between 96.5% and 100%. Antibody levels for virus types 1, 2, and 3, as measured by GMT (reciprocal value), were 277, 1017, and 222 for OPV, and 465, 526, and 758 for IPV, respectively. IPV appears to be perfectly acceptable as a substitute for OPV for primary vaccination.

Immunity of the Croatian population to poliomyelitis--a serosurvey.

Eight years after the last case of poliomyelitis it was of a special interest to determine the immunity level of the Croatian population to polio and thus to evaluate the possible risk of the revival of this infection. For this purpose, 200 sera samples were collected from individuals of different age and place of residence. Neutralizing antibodies (NT) for all three polioviruses were searched for. Antibody titers of > or = 1:8 were considered positive. Results of the study showed some 75% of the study subjects to have antibodies to polio type 1 and 2, and some 83% to type 3. Only 4% of the sera tested had no NT antibodies to any of the three types. The lowest mean geometric antibody titer (GMT) was for polio type 3 (GMT3 = 19.4; reciprocal value) and somewhat higher for type 1 (GMT1 = 23.5) and type 2 (GMT2 = 22.6). When the antibody titers were related with the age of the subjects, they were found not to decline with age, which was ascribed to periodical boosters with vaccinal strains. It is stressed that, in spite of the eradication of poliomyelitis achieved in Croatia, compulsory vaccination of the children should be continued until its global eradication.

[Immunity to diphtheria in the Croatian population in 1994]. / Imunost Hrvatskog pucanstva na difteriju 1994. godine.

The large outbreak of diphtheria in the former SSSR countries, which has been linked, among others, to low herd immunity, has led us to determine the level of this immunity in the Croatian population in view to undertake, if necessary, extra prophylactic measures (vaccination). For the purpose, C. diphtheriae serum antibody levels were determined in persons aged from 20 to above 60 years and coming from four major Croatian towns (Zagreb, Rijeka, Osijek and Split). A commercial ELISA test and neutralization test (NT) on guinea pig were used. Whereas 223 sera were examined with ELISA, only 51 underwent NT. Both tests showed herd immunity to decline gradually with age, ELISA also revealing a wide variation range of antibody concentrations by individual age groups (Table 1). There was not a single serum sample below the "critical" level of 0.01 IU/ml. in Table 2, ELISA results are classified in three groups by antibody level: up to 0.01 IU/ml, between 0.01 and 0.09 and above 0.09 IU/ml, i.e. as unprotected, partially protected and protected persons. Such grouping of findings shows that not one of the subjects belongs to the first category, that most of them belong to the third (68%), as well as that the latter are passing into the second with growing age. It is concluded that by carrying out the mandatory immunization programme, in force in Croatia, it has been possible to attain and to sustain a high level of herd immunity. Hence there is no need for booster immunizations at older age.

[Reactivity and immunogenicity of Havrix 360 vaccine for hepatitis A]. / Reaktogenost i imunogenost "Havrix 360" vakcine protiv hepatitisa A.

The reactogenicity and immunogenicity of a new vaccine against viral hepatitis A, under the name HAVRIX, manufactured by SmithKline Beecham Biologicals, Belgium, was studied. A single dose of 1 ml contains not less than 360 ELISA units of inactivated HAV, strain HM175, cultivated on human diploid cells. The vaccine has been applied intramuscularly to 80 second-grade primary school children under the 0, 1 and 6-month schedule. Postvaccinal reactions were followed for three days after each application of the vaccine. They were generally mild and present in less than 5% of the vaccinees (local as well as general). One month after the last vaccination the seroconversion was 100% in the anti HAV antibody test (HAVAB-ABBOT), the antibody level being over 500 IU/I, in 98% of the vaccinees. In conclusion, the tested vaccine is perfectly acceptable from both aspects, postvaccinal reactions and conferred protection. As the hepatitis A morbidity in Croatia has never been as low as in the last few years, the eventual introduction of this vaccination into the EPI is questionable.

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%.