Smallpox vaccination immunity in relation to number of insertions*

Bull. Org. mond. Sant } 1973, 48, 397400 Bull. Wid Hithi Org.J Smallpox vaccination immunity in relation to number of insertions* G. NYERGES,' L. ERDOS,2 & F. MELLY 3 The influence of the number of insertions of vaccine on smallpox vaccination immunity has been the subject of considerable controversy. In this study the problem was investigated in children ofcomparable age, sex, and smallpox vaccination history. The incidence ofpost- vaccinal fever and the antibody response of subjects given single and double insertions were compared. While single insertions causedfewer febrile reactions than double insertions, the difference was not significant. Successful vaccination invariably elicited a marked neutraliz- ing antibody response. However, subjects who received two insertions developed significantly higher antibody titres than subjects with a single insertion. In the revaccinated group the difference in titre was still demonstrable 16 months after vaccination. It is concluded that the number of insertions may play a role in the duration of vaccination immunity. The practice of multiple insertions of vaccine in smallpox vaccination has been gradually abandoned. In many countries vaccination is now performed by a single insertion, and in others two insertions are required although the vaccination is also regarded as successful if it produces one major reaction. The use of single insertions has several advantages: vaccina- tion is more rapid, less traumatic, and leaves only one scar. In addition, it is generally believed that the smaller the area of skin involved in vaccination, the lower the incidence of postvaccinal fever. In small- pox vaccination campaigns the single insertion tech- nique has economic benefits as well. In all probability no objection can be raised to the efficacy of the single insertion technique provided the vaccination is performed with fully potent vac- cine and perfect technique. No subjects with a recent successful single-insertion vaccination have been reported to contract smallpox. Lane et al. (1970) found a marked rise in neutralizing (NE) antibody titre in 60 % of subjects revaccinated by either single or double insertions. However, earlier reports suggested that postvac- cinal immunity increased with the number of inser- tions. In some cases it may be assumed that the * From the Vaccine Control Unit, National Institute of Public Health, Budapest, Hungary. Assistant Chief. Chief. 'Research Associate. potency of the vaccine was inadequate and that the multiple insertion technique actually increased the likelihood of successful vaccinia infection. Some reports, however, pointed to a relationship between the number of takes or the area of reaction and the immunity produced. According to Brownlee (1905) and Rao et al. (1960) the incidence of lethal smallpox among vaccinated persons varied inversely with the number of scars. Cross (1959) has reported that resistance to revaccination develops sooner in sub- jects with larger primary vaccination vesicles. In view of the importance of the question and the inconsistency of previous findings, studies were undertaken to compare the immunogenicity of the single and double insertion techniques in primary vaccinations and revaccinations and the respective incidence of adverse postvaccinal reactions. MATERIALS AND METHODS Vaccine Lyophilized Lister-strain vaccine (" HUMAN ", Budapest) was used. When reconstituted the vaccine had a potency of 34 x 10 10 pock-forming units per litre. The same vaccine lot was used throughout the investigation. Vaccination Subjects were divided at random into 2 groups of similar age and sex and were given either one or two 3022 -397- G. NYERGES ET AL. Table 1. Results of vaccination Number of vaccinees with Total Type of vaccination Number of number ofinsmertions no major one major two major vaccinees reaction reaction reactions primary vaccination 1 1 74 0 75 2 0 3 71 74 revaccination 1 0 107 0 107 2 0 1 98 99 insertions of vaccine. Vaccinations were performed with the multiple puncture method using bifurcated needles. In primary vaccinations 3 strokes were applied per insertion, and in revaccinations 15 strokes. Subjects Primary vaccination: 149 1-year-old infants. Revaccination: 206 12-year-old schoolchildren who had received their first vaccination at age 1 year. All had a distinctly visible primary vaccination scar. Reading of local reactions Reactions were read on the 7th postvaccinal day. The vaccination was regarded as successful if a pustule or an area of definite palpable induration surrounding a scab (a major reaction) could be seen. Recording offebrile reactions The afternoon temperature of the infants was recorded, by those caring for the children, every other day between the 7th and 14th postvaccinal days. Schoolchildren were asked, at the time when postvaccinal blood samples were taken, if they had had any fever after the vaccination. Blood collection Blood was taken from some infants 4 weeks after successful primary vaccination. Equal numbers of subjects from the single and double insertion groups were selected at random. The first samples from the schoolchildren were taken immediately before revaccination. Postvaccinal samples were drawn 3 weeks later from randomly selected children with successful single or double insertions. A third blood sample was collected 16 months after successful single or double revaccination, primarily from those whose first and second samples had already been examined. Serological methods Sera were inactivated at 56°C for 30 min and stored frozen. The haemagglutination-inhibition (HAI) and the NE test titres of the sera were de- termined. A 10 % preparation of normal human immunoglobulin was used as a reference preparation. It was titrated in every case simultaneously with the sera to be examined. HAI titrations were performed by the micromethod of Szathmary & Holik (1958). Titrations of NE antibodies were made on the chorioallantoic membranes of 12-day-old chick embryos, using 60 % pock reduction as the endpoint (Nyerges et al., 1966). RESULTS The results of vaccination are shown in Table 1. Among the 173 subjects vaccinated at two sites there were 4 who developed only one major reaction. For this reason it was decided that in the follow-up of the antibody response to double insertions, only sub- jects with two major reactions would be included. The incidence of febrile reactions is indicated in Table 2. Both after primary vaccination and after revaccination temperatures of over 38°C occurred more frequently in the double insertion group than Table 2. Incidence of febrile reactions in successfully vaccinated children Proportion Type Number of Number of of children with of vaccination insertions subjects 380C or higher(%) primary vaccination 1 75 22.7 2 74 29.7 revaccination 1 105 3.8 2 95 8.4 398 SMALLPOX VACCINATION Table 3. Distribution of HAI titres of successfully vaccinated children Type Number of Time of blood Number of Distribution of titres Geom. of vaccination insertions collection Nsuber D o t Gesomtested 2 4 8 16 32 64 titres primary 1 4 weeks after 33 0 0 4 8 13 8 27.0 vaccination vaccination 2 28 0 0 2 4 1 2 1 0 33.6 revaccination I before revaccination 38 19 11 5 3 0 0 3.5 3 weeks after revaccination 38 2 4 13 10 9 0 11.5 2 before revaccination 39 14 12 8 4 1 0 4.4 3 weeks after revaccination 39 0 2 12 14 10 1 14.9 in those given a single insertion, although the cination. This statistically significant difference was observed differences were not statistically significant still demonstrable in the blood samples taken at the 5 % level. In any event, even if there was a true 16 months after revaccination. difference it was not a serious one. The results of the HAI and NE tests are shown in DISCUSSION Tables 3 and 4 respectively. No difference in HAI titre could be detected in relation to the number of Our finding concerning the frequency of serological insertions. The NE antibody response, however, was reactors in the single insertion and double insertion not identical in the single and double insertion groups is in agreement with the report of Lane et al. groups. Although successful vaccination elicited con- (1970). However, when comparing the postvaccinal siderable NE antibody production in every subject, NE antibody titre values, one finds that two inser- the mean postvaccinal NE antibody titre after two tions were more effective than a single insertion. insertions was significantly higher than after a single Both in primary vaccination and in revaccination, insertion for both primary vaccination and revac- subjects in the double insertion group exhibited Table 4. Distribution of NE antibody titres of successfully vaccinated children Type of Number of Time of blood Number of Distribution of titres Geom. vaccination insertions collection subjects mean oftested < 4 4 16 64 256 1024 4096 titres primary 1 4 weeks after 26 0 1 8 17 0 0 0 37.5 vaccination vaccination 2 26 0 0 4 17 4 1 0 70.8 before revaccination 30 14 13 3 0 0 0 0 3.3 1 3 weeks after revaccination 30 0 0 8 13 9 0 0 66.7 16 months after revaccination revaccination 30 1 6 16 7 0 0 0 15.7 before revaccination 29 13 13 2 1 0 0 0 3.6 2 3 weeks after 31 0 0 0 10 14 6 1 233.8 revaccination 16 months after revaccination 29 1 6 5 12 5 0 0 32.0 399 400 G. NYERGES ET AL. significantly higher neutralization titres than persons given a single insertion of vaccine. The question arises whether this difference has any practical implications. Do the lower titres obtained after a single insertion entail any risk of imperfect protection? The answer of course is a definite no. Epidemiological data have shown that a successful vaccination confers safe pro- tection against smallpox for 4-5 years. There has been no indication that within this period of time the immunity provided by one insertion is insufficient. Nevertheless, as the difference in titres can be demon- strated not only some weeks but even 16 months after vaccination, it might be assumed that two takes provide more durable immunity. This would indicate that the advantage and practical value of double insertions will continue to be evident many years after vaccination. Clinical observations relating the number of lethal cases of smallpox in a vaccinated population to the number of scars are in accordance with this assumption. Though fever occurred some- what more frequently among subjects given double insertions of vaccine, the difference was not sig- nificant and hence would not be a contraindication to the use of this technique. ACKNOWLEDGEMENTS The authors thank Dr J. Szigethy and Dr Gy. Jenay in Sz6kesfeh6rvAr for providing the opportunity to conduct the field investigation. Thanks are also expressed to Mrs I. Varjask6ry, Mrs P. Balcsik, Miss M. Antony, and Mrs M. Komiromy for their valuable technical assistance. RXSUMt IMMUNITE CONFtRPE PAR LA VACCINATION ANTIVARIOLIQUE EN FONCTION DU NOMBRE D'INOCULATIONS On a pratiqu6 la primovaccination antivariolique chez 149 nourrissons ag6s de 1 an et revaccin6 206 eco- liers ag6s de 12 ans en utilisant le meme lot de vaccin. Dans les deux groupes, la moiti6 des enfants n'a reru qu'une seule inoculation de vaccin tandis que l'autre moiti6 subissait deux inoculations simultan6es. La r6ponse s6rologique a et6 recherch6e par titrage des anticorps inhibant l'h6magglutination (IH) et neutralisants (N) dans des 6chantillons de sang recueillis 4 semaines apr6s la vaccination chez les primovaccin6s, et, en cas de revaccination, imm6diatement avant, apres 3 semaines et apres 16 mois. On a relev6 une incidence l6gerement plus 6lev6e des r6actions f6briles postvaccinales parmi les sujets ayant requ deux inoculations. Chez les primovaccines et chez les revaccin6s, aucune difference des titres d'anticorps IH postvaccinaux ne s'est manifestee en fonction du nombre d'inoculations. En cas de prise, la reponse en anticorps N a 6t6 chaque fois notable. Toutefois, tant parmi les primovaccin6s que parmi les revaccin6s, les sujets ayant requ deux inoculations ont pr6sente apres 3 ou 4 semaines des titres d'anticorps N nettement plus 6leves que les sujets immunis6s par une seule inoculation. La diff6rence, statistiquemnent significative, a e retrouv6e lors des examens serologiques pratiqu6s au 16e mois. D'apr6s les auteurs, ces observations tendent a prouver que le nombre des inoculations joue un r8le dans la duree de l'immunite succedant a la vaccination antivariolique. REFERENCES Brownlee, J. (1905) Biometrika, 4, 313 Cross, R. M. (1959) Lancet, 1, 1092 Lane, J. L. et al. (1970) Publ. Hlth Rep., 85, 928 Nyerges, G. et al. (1966) Acta microbiol. Acad. Sci. hung., 13, 97. Rao, A. R. et al. (1960) J. Indian med. Ass., 35, 296 Szathmiry, J. & Holik, S. (1958) Acta microbiol. Acad. Sci. hung., 5, 329