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Formalin-inactivated polio vaccine has been used in the Netherlands since 1957. Within 3 years all children born in 1945 and later were offered vaccine. In the first years poliovaccine from different manufacturers were used. In 1961 a vaccine produced in the Netherlands by the ‘Rijks Instituut voor de Volksgezondheid’ (National Institute of Public Health) became available and in 1962 the poliomyelitis components were incorporated in a quadruple vaccine, which contains 15 Lf diphtheria, 5 Lf tetanus toxoid and 16 × 109Bordetella pertussis organisms in addition to the three polio components. As an adjuvant this quadruple vaccine contains 1·5 mg. aluminium phosphate per 1 ml. dose. For infants the schedule became three doses at ages 3, 4 and 5 months respectively, followed by a booster dose at the end of the first year. The over-all acceptance rate can be estimated at almost 90% of those eligible, but there were pockets in the population with lower rates.Since 1924 poliomyelitis has been a notifiable disease. During and after the last World War major epidemics occurred.The poliomyelitis morbidity rates in the 8 post-vaccination years 1958–65 were compared with those from two preceding 4-year periods 1950–3 and 1954–7. In the 1–4-year-old children, who presented the most vulnerable age group, paralytic poliomyelitis was reduced by about 97 % and in the other age groups this percentage was slightly less. The over-all reduction was 96 %. Comparison of the morbidity rates of non-vaccinated persons in 1958–65 with the rates from 1950–3 and 1954–7 gave an impression of the extent of the herd immunity. These rates were reduced 70–80 % in the children under 15 years and 90–95 % in those over this age. The individual protection given to the vaccinated was calculated from the morbidity rates in non-vaccinated, incompletely and fully vaccinated persons in the 1958–65 period. The reduction of morbidity was 90–95% for children of 1–14 years who got three doses or more and about 85 % for those who had only 1 or 2 doses. Fully vaccinated children, who are profiting from both individual protection and herd immunity, showed a reduction of 97–99 %.From the data presented it is concluded that vaccination with inactivated poliomyelitis vaccine can provide very effective protection for the individual and the community provided that a vaccine of good quality is used and the rate of acceptance is 75 % or better.

Methods for potency testing of inactivated poliomyelitis-vaccines are still inaccurate. Moreover, the lack of a suitable standard preparation of the vaccine can be felt as a major drawback.Sueh a standard preparation has to fulfill the requirement, that it is stable for a long period. Lyophilization is considered as a very satisfactory method to enhance the stability of biologic products (1).Here some experiments on the lyophilization of inactivated poliovaccines, which have led to a partial success, will be described.Trivalent vaccine lots Nos. 0029, 0031 and 0036, which were routinely produced in our laboratory (trypsinized monkey kidney cells, T. C. medium 199, peniciltine and streptomyeine added as antibiotics) were used in these experiments. The poliovaecines were mixed with an equal amount of solution of 10% pepton and 10~o sorbitol in MeIlvain buffer. This method was introduced in our laboratories for the lyophilization of smallpox vaccine by Brans (2).In this study ampoules containing 1 nil. of the above-mentioned mixtures were shellfrozen at --70 ~ C. Subsequently these ampoules were freeze-dried at --20 ~ C, for 8 hours, followed by drying above PeO~ at room temperature for 14 hours. The final product was stored at +4 ~ C.To test the potencies of our preparations, four groups of three week old chickens were injected intramuscularly, respectively with the dilution 1 : 10, 1:50, 1 : I25 and 1:625 of one dose of the test material. A reference

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The members of the Columbia SK group of viruses (Columbia SK, MM, EMC, Mengo virus) are closely related with regard to their pathogenic and immunologic properties. They are highy pathogenic for rodents (mice, cotton rats, hamsters, guinea pigs) following inoculation by intracerebral as well as by peripheral route. The inoculation results in a fatal encephalomyelitis, which may be accompanied by myocarditis, or, foliowing intramuscular inoculation, by myositis (Rustigian and Pappenheimer I6. ) As has been shown by Jungeblut 1~ and by Verlinde et al. 21, eynomolgus monkeys are also susceptible to intracerebrai and peripheral inoculation, which results in ~ disease clinically and histologically resembling experimental poliomyelitis with a short incubation period. The experimental disease, however, is transmissible from monkey to monkey only in a few passages, and infectivity of the monkey-passage virus for mice, and haemagglutinating ability fall rapidly.The immunologic relationship between the viruses of the Columbia SK group has frequently been shown by cross-neutralization (Jungeblut 9, Schatz and Plager is, Dic]c 4, Warren, Smadel and Russ 25, Olitz/cy and Yager r~, de Baan~).