Poliomyelitis: epidemiology and prophylaxis

Bull. Org. mond. Sante 1973, 48, 429-433 Bull. Wid Hlth Org.J Poliomyelitis: epidemiology and prophylaxis 2. Distribution of oral trivalent vaccine by lay volunteers * D. METSELAAR,' S. K. DOLA,2 & W. GEMERT8 In contrast to other vaccines, oral poliomyelitis vaccine is ingested, in the form of drops. In countries with insufficient health personnel, countrywide vaccination campaigns should therefore be possible at little cost if use is made of lay volunteers. The feasibility ofsuch a method was tested in apilotproject carried out in a district ofKenya. The response of volunteers and parents was good and coverage of the susceptible child population was sufficient to recommend this methodfor a countrywide campaign in the event ofa threatening epidemic. Alternatively, such a team could travel around the country, organizing campaigns in one district after another. Because epidemics in Kenya occur at regular intervals the territory should be covered within 3 years. Observations by Nottay & Metselaar (1973) have shown that a 3-year rhythm in the circulation of type 1 poliovirus is, at present, a basic factor in the epidemiology of poliomyelitis in Kenya. Of the patients seen in a 7-year survey, 99% were under 6 years of age. Two attempts to prevent expected epidemics by mass vaccination, making use of the normal facilities and staff of the Health Service, were only partly successful. It was therefore thought useful to find out whether the ease of distribution of oral (Sabin) vaccine would allow better coverage of the susceptible child population and could pro- vide a handy means of controlling the epidemic expected by the end of 1971. Considering that, in developing countries, the third distribution of this vaccine is frequently poorly attended and that Sabin et al. (1960) observed satisfactory conversion rates after two distributions, we decided to restrict the experiment to two rounds. We tried to overcome the handicap of interference by giving the vaccine to large groups of children in 1 or 2 days (Sabin et al., 1960). GENERAL OUTLINE OF THE EXPERIMENT AND PREPARATIONS We aimed at an administrative area of a size such that, if the method of vaccination could be used * From the Medical Research Centre (Department of the Royal Tropical Institute of Amsterdam), Nairobi, Kenya. Virologist. ' District Medical Officer, Kiambu District, Kenya. Statistician. there with success, it could be applied with con- fidence to the whole of Kenya. The order of adminis- trative units of the country is from provinces to sublocations via districts, divisions, and locations. The chief administrative officer of a district is the district commissioner; of a division, the district officer; of a location, the chief; and, of a subloca- tion, the subchief. It was decided to vaccinate the children of a district. First, pilot studies were performed in 3 locations. In one, 97.5% of the children attended at least once and 67.5% twice. The attendance rates in the other two locations were much lower: in one of them, 71 % of children under 6 years of age were vaccinated once, and 36% twice, the corresponding percentages for the other location being 55 and 20. In those two locations we studied the immunity status of the child population before and after vaccination and the ex- tent to which enteroviruses could have an adverse effect on the results of vaccination. To that end, 6 drops of fingerprick blood were collected in tissue culture medium from 176 children under 4 years of age who were attending dispensaries. Each of the sera was brought up to a 1-in-20 dilution and tested against about 100 TCD5o of poliovirus type 1 in 2 tubes of primary baboon kidney cells or Vero cells. We succeeded in obtaining a second blood sample from only 18 children. Faecal specimens, collected on swabs, were inoculated into 3 tubes of baboon kidney cells and into a litter of mice. In all, 205 spe- cimens were processed. For the larger vaccination experiment we chose 3027 -429 40. METSELAAR ET AL. Kiambu district, which has 5 divisions. According to the Kenya Population Census, 1969, about 105 000 children under 6 years of age (25% of the total population) were then living in the district. The organization of the vaccination campaign was delegated as far as possible to the administrative officers, most of the burden falling on the lowest ranks-the subchiefs. The district commissioner organized meetings in all 5 divisions for the district officers with their chiefs and subchiefs. At these meet- ings the purpose of the vaccination experiment and the way in which the programme was to be executed was explained by one of us. Each round had been planned to last 5 weeks: 1 week per division. The vaccine was to be distributed on Wednesdays and Thursdays, leaving the choice to the parents. During the meetings the chiefs and subchiefs decided on the vaccination centres. As a rule, the centres were so situated that mothers did not need to walk more than 11/2 km. Although people in Kenya usually live on their garden plots, not in villages, it frequently happened that several hundred children came to one centre. The subchiefs undertook to appoint the two or three volunteers who would do the vaccinations at each centre, and were made responsible for inform- ing the population about places and dates. The vac- cine was to be brought frozen to the centres on the morning of the vaccination days. In the afternoon any unused vaccine was to be collected and refrozen. On several occasions we have tested vaccine handled in this way and have not observed a substantial loss of titre. Depending on the programme of the day, 3-6 cars were to be available for the distribution and collection of the vaccine. The Monday before the vaccination days of the first round, the volunteers were instructed how to handle the vaccine bottle (a squeeze-type device on the bottle made it easy to produce two drops) and how to give the drops straight into the mouths of the children. It was stressed that under no circum- stances should vaccine be given to primary-school children, children 6 years of age or older, or those that had shed their upper front teeth. Written instruc- tions and posters were also supplied to the volunteers. In all but two locations, one sublocation was chosen randomly for the evaluation. A few more volunteers who had been appointed at the centres of these sublocations were requested to enter certain details on a card for each child who received the vaccine for the first time. The cards were to be given to the mothers with the request to keep them for the second round and/or the evaluation. Subchiefs or policemen acted as guides to the drivers, who received a list of the vaccination centres to be visited and, for each centre, the appropriate number of bottles of vaccine. The number of bottles (100 vaccine doses per bottle) necessary for each centre was estimated from the 1969 population census figures. The drivers were instructed to adjust the number of bottles where necessary. EXECUTION OF THE EXPERIMENT On the whole the experiment went according to plan. It was not always easy to obtain cars when they were required. Once, one car had to do the work of two, which somewhat upset the programme in the area concerned for 2 days. One meeting for the instruction of volunteers could not be held because a subchief defaulted. With that exception, chiefs, subchiefs, and volunteers attended in time. In many locations the number of children vacci- nated on the second day of the first round was very small. Moreover, some divisions were large and the vaccine arrived late at some centres. It was decided, therefore, to reopen the vaccination centres on 1 day only for the second round and to divide 3 of the 5 divisions into 2 parts. The second round was thereby completed in 8 vaccination days and 24 " car-days ", against 10 vaccination days and 36 (planned: 38) car-days for the first round. The interval between the 2 rounds was 8-10 weeks. EVALUATION The evaluation in the randomly chosen subloca- tions was carried out according to the method described by Geser et al. (1970). Names were ran- domly chosen from lists of taxpayers, which contain the names of practically all heads of households. The houses of the chosen taxpayers served as the starting points from which clusters of houses were visited. The total number of children under 6 years of age and the number of such children with cards were counted in each household. Children more than 6 years old with cards were counted separately. An explanation was requested when children under 6 years of age had missed one or both vaccinations. The number of randomly chosen sublocations ranged between 2 and 5, depending on the size of the division. For the sublocations, the number of clusters ranged between 1 and 4 and the number of households included in a cluster, between 10 and 35. Samples were taken in 16 sublocations, the target 430 POLIOMYELITIS: 2 being a sample of 10% of the children under 6 years of age in each sublocation. RESULTS During the first round, 121 000 doses were given; during the second round, 97 000. For an estimated 105 000 children under 6 years of age, the figure for the first round is, of course, peculiar. The evaluation gave a clearer insight into the attendance. On the average, 73% of children attended once and 46% attended twice. The percentage of those who attended at least once ranged from 28 to 88 for the sub- locations that were evaluated. For two attendances, the minimum and maximum percentages were 10 and 74, respectively. The results of the evaluation are given in detail in Table 1. If the census figures of 1969 were cor- rect, the number of children actually sampled was around 12.5% of the total child population of the sublocations included in the evaluation. The 95% confidence intervals are so wide because most cal- culated estimates are based on ratios (Cochran, 1962) (households were sampled but the calculations were made for children). There is a fair chance that the children who were not vaccinated will be infected by a sibling living in the same house (see, for example, Fox, 1961). Figures are therefore given for households also. As 21 % of the households with children under 6 years of age were not reached at all, and 38% were completely covered, it is clear that, in about 40% of households, at least one child was vaccinated once or twice. About one-quarter of those children were over 6 years of age. In the 2 sublocations sampled, the percentage of children with antibodies against type 1 poliovirus rose from 56 (18 of 32) in the 6-11-month age group to 92 (48 of 52) in the 3-year age group. In 13 of the 18 children from whom serum spe- cimens were taken before and 4 weeks after the vaccination campaign, both specimens were posi- tive; in 2, they were negative; and, in 3, they had converted from negative to positive. Virus was isolated from 55 of the 205 anal swabs (27%): poliovirus (all 3 types) from 15 swabs and other enteroviruses from the remaining 40. DISCUSSION Attendance during the second round was lower than during the first. Although the number of doses given was frequently in excess of the estimated num- ber of children at a sublocation, 100% coverage was never reached-not even for the children who received at least one dose. This observation shows the importance of a proper evaluation. The discrepancies may have resulted from wastage (too many drops given to each child vaccinated) or from the vaccination of many children over 5 years of age. The latter supposition was confirmed by the evaluation. " We did not know " was the explanation most frequently given for failure to attend. It had been the duty of the subchiefs to spread information about the vaccination to the parents and guardians of the children. Many did admirably well; regrettably, a few failed. We had the impression that parents were will- ing to take advantage of the opportunity to have their children vaccinated. Probably it would have been better if the dates for the second distribution could have been fixed at the same time as those for the first. That would have made the second round less dependent on the subchiefs, who failed more frequently to disseminate the information on the second occasion. No attempt was made to evaluate the cost of the experiment. Experience has shown that 1 day per vaccination round is sufficient; to allow a second day is not economical. It is hoped that the coverage reached was suf- ficiently high to prevent counteracting interference by wild enteroviruses. The carrier rate of 27% should be regarded as minimal because anal swabs were used. The rate is of the same order as that found by B. Nottay (unpublished observations) in Nairobi. Of 2 925 faecal specimens collected in a 4-year survey of children attending health clinics, 31.3% were positive for enteroviruses other than poliovirus. Since, in our two sublocations, vaccine had been given at dispensaries about 3 months earlier, most or all of the 15 poliovirus isolates may have been of vaccinal origin. Under the conditions of hygiene prevailing in large areas of Kenya, vaccine virus may circulate longer and spread farther than has been observed (Fox, 1961) in more highly developed countries, and the immediate adverse effect of inter- ference by enteroviruses other than poliovirus could be balanced by the prolonged circulation of vaccinal strains. The coverage attained by the use of lay volunteers is much better than that usually achieved by health centres and dispensaries in rural areas. At most, 20% of the children living around these institutions 431 D. METSELAAR ET AL. 0 Co N 00 CO < Co Co _ 0O v Co00_ o Ns) N _ _ _ Cv N N N ) )C Mt 0) o _o o Co N C.) 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We think it is justified to consider polio- myelitis vaccination separately from the " routine " vaccinations until budgetary provision can be made for its inclusion in a comprehensive programme. Combinations with other easily performed vaccina- tions should, of course, be attempted. A programme of nationwide poliomyelitis vaccina- tion by lay volunteers can be considered useful as an emergency measure only when an epidemic threatens. In Kenya the regular rhythm of type 1 poliovirus circulation, with the threat of epidemics every 3 years, makes it useful to have such a means at hand. Thus the method was used early in 1972 (Koinange et al., 1973). A vaccination programme of this kind may be executed as part of the regular programme of the public health service. In that case, a small professional team, equipped with vehicles and with facilities for carrying vaccine in the frozen state, can carry out vaccinations in one district after another, covering the country within 3 years. This system has the advantage of being inde- pendent of other departments-e.g., for transport. Under the present circumstances vaccination could be restricted to children under 4 years of age. This would save vaccinating children who are already immune, and so avoid wastage of vaccine. Care should be taken, when ordering vaccine to be distributed in mass campaigns, to ensure that the design of the bottles allows easy application. ACKNOWLEDGEMENTS We are indebted to the Director of Medical Services, Government of Kenya, for providing the vaccine used in this experiment. The interest and active assistance of Mr Kang'ethe, District Commissioner of Kiambu District, and of the district officers and many chiefs and subchiefs. as well as the participation of numerous volunteers, are gratefully acknowledged. RItSUMIt POLIOMYELITE: EPIDEMIOLOGIE ET PROPHYLAXIE: 2. DISTRIBUTION DE VACCIN BUCCAL TRIVALENT PAR DU PERSONNEL BENEVOLE NON QUALIFIE Le vaccin antipoliomyelitique buccal etant administre sous forme de gouttes, il devrait etre possible, dans les pays qui ne disposent pas de personnel de santd en nombre suffisant, d'organiser des campagnes de vaccina- tion en recourant 'a la collaboration de personnel bdne- vole. Un projet pilote destine a evaluer la praticabilit6 de la methode a ete men6 dans un district du Kenya. On s'est borne a distribuer deux doses. Au cours d'un essai preliminaire, 97,5% des enfants se sont presentes a une seance de vaccination et 67,5% a deux s6ances. On a ensuite etendu le projet a l'ensemble du district de Kiambu, comptant une population d'environ 105 000 enfants de moins de 6 ans. La responsabilitd de l'organi- sation des distributions de vaccin et du choix des volon- taires a ete confi6e dans la mesure du possible aux divers echelons administratifs. Les centres de vaccination ont ete choisis de telle sorte que les meres et les enfants ne doivent pas parcourir plus de 1,5 km pour s'y rendre. Les volontaires ont regu les instructions necessaires. En moyenne, 73 % des enfants ont participe a une seance de vaccination et 46% a deux seances. Les raisons des absences, notamment lors de la 2e distribution, sont evoquees. On estime que la couverture obtenue en con- fiant la distribution du vaccin a du personnel benevole non qualifie est de loin superieure a celle obtenue par la vaccination dans les centres de sante et les dispensaires des regions rurales. La methode pourrait etre etendue a l'ensemble du territoire, comme mesure d'urgence, en cas de menace d'une epidemie de poliomyelite. REFERENCES Cochran, W. G. (1962) Sampling techniques, 2nd ed., New York, Wiley Fox, J. P. (1961) In: Chumakov, M. P., ed., Fourth Scientific Conference on Live Poliovirus Vaccine, Mos- cow, 17-20 May 1960, Moscow, Academy of Medical Sciences of the USSR, pp. 531-545 Geser, A. et al. (1970) Bull. Wid Hlth Org., 43, 521-537 Koinange, W. et al. (1973) Bull. Wld Hlth Org., 48, in press Nottay, B. K. & Metselaar, D. (1973) Bull. Wld Hlth Org., 48, 421-427 Sabin, A. B. et al. (1960) J. Amer. med. Ass., 173, 1521- 1526 Schofield, F. D. et al. (1972) In: Proceedings of the Semi- nar on Immunizations in Africa, Kampala, 7-10 Decem- ber 1971, Paris, Centre international de l'Enfance, pp. 293-298