Rubella immunization of teenage girls in Iceland and follow-up after a severe rubella epidemic

Bldletin of the World Health Organization, 60 (1): 141 - 146 (1982) Rubella immunization of teenage girls in Iceland and follow-up after a severe rubella epidemic BJORG RAFNAR 1 Of 730 Icelandic schoolgirls, 12 years of age, screened for rubella antibodies by the haemagglutination-inhibition (HI) technique, 372 (50.9%) werefound to be seronegative. Rubella vaccine was administered to 355 members of this group, and to 12 girls with an HI titre of20. Blood samples were taken 6 weeks and 1 year after immunizationfrom 336pre- viously seronegative girls andfrom the 12 low-positive vaccinees, and testedfor HI anti- bodies. The seroconversion rate was 99.15%. One year after immunization, 94.8% of the girls tested had an HI antibody titre of40 or more. The geometric mean titre (GMT) ofthe previouslyseronegative girls was 62.07at 6 weeksand 61.69 at oneyear after vaccination. Of the girls with an initially lowpositive titre, only3 (25%o) showeda significant rise. TheGMT was 40 at 6 weeks, butfell to 25.2 after 1 year. Re-immunization had no effect on antibody levels in either group. A severe rubella epidemic occurred 2 years after immunization, following which 345 vaccinees and 193 naturally immune controls were studied. Allsubjects had been exposed to wild rubella virus at school, and rubella cases had occurred in the homes of 116 vaccinees (33.6%)o and 41 control subjects (21.2%o). Only 5 (1.5%o) primarily seronegative vaccinees and 2 unimmunized controls (1%o) showed serological evidence of infection during the epidemic. Immunization of seronegative females against rubella was started in Iceland in January 1977 in order to try to eradicate congenital disease. Schoolgirls aged 12 years were selected for routine screening, and sero- negative subjects were given rubella vaccine. The present report describes a study of immunity in this age group after immunization with RA/27/3 rubella vaccine. The subjects were examined after one year in a rubella-free environment, and after exposure to wild rubella in an epidemic that occurred at the end of the second year after immunization. EPIDEMIOLOGICAL BACKGROUND In Iceland rubella occurs in well defined epidemics between which the virus seems to disappear. A major rubella epidemic began in the autumn of 1963, reached a sharp peak in December and January, and then faded out over the next 3 months; no cases were recorded after midsummer 1964. Children born in 1964 may have been infected as newborns and intra- uterine infections may have occurred during the epi- demic. There were no further rubella outbreaks until ' Department of Microbiology, University of Iceland, PO Box 855, Eiriksgata, Reykjavik, Iceland. December 1972, when an epidemic occurred which lasted until 1975, but never reached a sharp peak. The greatest number of cases was recorded in 1973. Serological tests for rubella are done for the whole country in one laboratory and the service is widely used if rubelliform exanthema occurs among contacts of pregnant women. Between October 1975 and May 1978, complement-fixation (CF) and haemaggluti- nation-inhibition (HI) tests for rubella were negative, and it can therefore be assumed that Iceland was free from the disease during this period. In May 1978 rubella cases began to occur in a northern town, Akureyri, and from there the epi- demic spread west and south during the summer, reaching a sharp peak in Reykjavik in December and January. The epidemic then faded out quickly in the following three months, repeating the pattern seen in the epidemic of 1963 - 64. MATERIALS AND METHODS Study group A group of 730 schoolgirls, born in 1964 and attending elementary schools in Reykjavik, were screened for rubella antibodies by the haemag- 4156 -141- 142 B. RAFNAR glutination-inhibition (HI) technique. The sero- negative girls (group A) and those with a titre of 20 (group B) were immunized, if responsible relatives gave written permission, with Almevax (Wistar RA/27/3),a given subcutaneously in the upper arm. All vaccinees were asked to report any subsequent illness, and were later questioned about any side- effects of the immunization. In order to study the response to the vaccine, blood samples were collected 6 weeks and 1 year after immunization. Girls with an HI titre < 20 were re- immunized one year after the primary immunization, in April 1978, and blood samples were again collected and tested six weeks later. In March 1979, shortly after the peak of a severe rubella epidemic in Reykjavik, blood samples were collected from the vaccinees and from a control group of 193 unimmunized female classmates, who had been found to be naturally immune to rubella in the primary screening. The vaccinees in this follow-up study included all the re-immunized girls. All girls tested after the epidemic were asked whether there had been cases of rubella among their family or close friends, and any occurrence of exanthema or arthralgia in the winter of 1978 - 79 was recorded. Test methods Venous blood was collected into Vacutainers and the sera separated on the same day by centrifugation at 1380 g for 10 min. The sera were transferred into sterile vials and kept at -25 °C until tested and between tests. The HI test and the single radial haemolysis (SRH) method have been described previously (1). An HI antibody titre of 10 or less was taken as negative and a titre of 20 as low positive. In the SRH test, a haemolytic zone of diameter 8.5 mm or greater was considered positive; the SRH test was used only to confirm immunity and was not considered as a quantitative assay. In the complement-fixation (CF) tests, the long- fixation macrotechnique described by Grist et al. (2) was used. The lowest serum dilution was 1:4 and complement fixation at this dilution was considered the lowest positive reaction. In the original screening and in the tests done in the first year after immunization, only HI antibody titres were measured. Paired sera taken from vaccinees at 6 weeks and 1 year after immunization were tested together.b In the follow-up after the epidemic, paired sera taken from girls one year after immunization and after the epidemic were tested together by both HI e From Burroughs Wellcome, Beckenham, Kent, England. b Lyophilized rubella haemagglutinin (HA) antigen supplied by Flow Laboratories, Irvine, Scotland. and SRH tests.c For the control group, the sample taken after the epidemic was tested together with the sample originally taken for screening. In addition, 161 paired sera from vaccinees and 77 paired sera from the control group, taken from heavily exposed individuals, were tested by CF. RESULTS Of the 730 schoolgirls screened for rubella anti- bodies, 346 (47.5%) were seropositive (HI titre > 40), 372 (50.9%) were seronegative, and 12 (1.6%o) had a titre of 20. Altogether, 367 girls were immunized with RA/27/3 rubella vaccine. The immunization did not produce any long-lasting side-effects, and vaccinees reported very minor complaints only. Of the 353 girls tested after immunization, only 3 had no detectable HI antibodies, giving a seroconversion rate of 99.15%o. One year after immunization, 326 (94.8%) of 344 subjects had an antibody titre of 40 or more, while 19 girls in group A and 6 in group B had a titre of 20 or less. Of this group, 17 girls from group A and 5 from group B were re-immunized in April 1978 and blood again collected and tested 6 weeks later. It is very unlikely that there was any contact with wild rubella virus during this first year. HI antibody levels in paired sera taken from 336 vaccinees in group A at 6 weeks and one year after immunization are shown in Table 1. The geometric mean titre (GMT) was 62.07 6 weeks after immunization and 61.69 after one year. During the peak of the rubella epidemic of 1978-79, all the vaccinees were exposed to wild c Lyophilized rubella HA antigen supplied by Orion, Helsinki, Finland. Table 1. HI antibody titre in sera from 336 previously seronegative girls, 6 weeks and 1 year after immuniz- ation HI titre HI titre 6 weeks after immunization 1 year after immunization 10 20 40 80 160 320 10 2 2 0 0 0 0 20 0 5 8 1 1 0 40 0 11 74 40 5 0 80 0 2 45 74 21 2 160 0 0 3 19 14 4 320 0 0 1 1 1 0 a The first sample was taken 5 weeks after immunization. RUBELLA IMMUNIZATION IN ICELAND virus. Clinical rubella cases occurred among their unimmunized male classmates and among family members in 116 of the 345 households. Thus, 33.6% of the vaccinees were in close contact with rubella at home, in addition to being exposed at school. Cases of rubella occurred in 41 (21.2%) of the 193 house- holds of naturally immune controls. Of the vaccinees, 30 (8.7%) complained ofexanthema and 24 (7.0%) of arthralgia at some time during the epidemic. In the control group, 15 (7.8%) complained of exanthema and 16 (8.3%) of arthralgia. In Tables 2, 3, and 4, the results of HI, SRH, and CF tests in immunized and control subjects are compared before and after the epidemic. Of the 333 immunized girls in group A, 328 (98.5%) showed no rise in antibody titre. This included all those who complained of arthralgia, and 28 of the 30 who complained of exanthema during the epidemic. The complaints were therefore considered not to be due to rubella. Five immunized girls (1.5%), and 2 naturally immune girls (1%) showed a signifi- cant rise in HI and/or CF antibody titres. Two of the vaccinees had had a general rubelliform exanthem lasting for a few days during the epidemic, but no other sign of illness. The 3 other vaccinees and the un- immunized girls had no signs of clinical rubella. Table 2. Hi antibody levels in sera from 333 immunized girls and 193 control subjects with natural immunity, before and after a rubella epidemic HI titre after Hi titre before the epidemic the epidemic 10 20 40 80 160 320 Vaccinees 10 2 1 0 0 0 0 20 0 25 13 0 0 0 40 0 7 181 31 0 0 80 0 0 11 55 1 0 160 0 0 3 3 0 0 320 0 0 0 0 0 0 Control subjects 10 0 0 0 0 0 0 20 0 3 2 0 0 0 40 0 1 42 15 0 0 80 0 0 5 86 10 0 160 0 0 1 8 17 0 320 0 1 0 0 0 2 Table 3. Antibody levels, as measured by SRH, in sera from 333 immunized girls and 193 control subjects with natural immunity before and after a rubella epidemic Haemolytic Haemolytic zone diameter before the epidemic zone diameter (mm) after the epidemic (mm) 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0 13.5 Vaccinees 6.5 1 8.0 1 8.5 1 5 5 9.0 5 35 14 1 1 9.5 1 14 51 27 3 1 10.0 1 18 44 18 1 1 10.5 1 10 24 12 1 1 11.0 2 3 14 3 11.5 1 5 1 3 12.0 1 1 1 Control subjects 8.5 2 1 9.0 1 7 5 1 9.5 8 10 11 1 10.0 12 20 15 10.5 2 10 20 10 2 11.0 2 7 11 4 1 11.5 1 9 3 12.0 2 8 1 12.5 2 2 1 13.0 1 143 B. RAFNAR Table 4. CF antibody levels in sera from 149 immunized girls and 77 control subjects with natural immunity, before and after a rubella epidemic CF titre before the epidemic CF titre after the epidemic < 4 4 8 16 32 64 128 Vaccinees <4 5 0 4 0 0 0 0 4 1 9 10 1 0 0 0 8 0 2 44 26 0 0 0 16 0 1 3 32 4 0 0 32 0 0 2 1 2 1 0 64 0 0 0 1 0 0 0 Control subjects <4 0 0 1 0 0 0 0 4 0 2 6 0 0 0 0 8 0 1 15 12 0 0 0 16 0 0 0 18 5 0 0 32 0 0 1 2 6 3 0 64 0 0 1 0 0 3 0 128 0 0 0 0 0 1 0 Table 5 shows the HI, SRH, and CF antibody titres in the serum samples taken from the 12 vaccinees in group B, who initially had a low positive HI titre. When SRH tests were carried out on their pre- immunization specimens, 8 of the 12 samples were found to be positive (diameter of haemolytic zone, 8.5 - 10 mm), and 4 were considered negative (zone diameter between 7 and 8 mm). Six weeks after immu- nization, all the girls had haemolytic zones > 8.5 mm in diameter, but only 3 of the 12 (25%) showed a significant rise in titre in the HI test. During the first year the geometric mean titre (GMT) in this group fell from 40.0 at 6 weeks after immunization to 25.2. None of the 5 re-immunized girls showed a significant rise in antibody titre after re-immunization and none in group B showed serological signs of infection during the rubella epidemic. When the 17 re-immunized girls from groupA were tested for SRH and HI antibodies, 13 who had sero- converted after the primary immunization showed no increase in HI or SRH antibodies after re-immuniz- ation or after the epidemic. One girl whose initial HI titre was 10 (SRH diameter 9 mm) showed no signifi- cant rise in titre after primary immunization, after re- immunization, or after the epidemic. One girl, who was negative in all tests initially, increased her SRH antibody level to 9.5 mm 6 weeks after primary immunization, but was negative in all tests 1 year later. She gave negative results again 6 weeks after re- immunization and also after the epidemic. Her mother had a history of clinical rubella in 1963 when 3 - 4 months pregnant, although the girl showed no signs of congenital rubella. She may have had neutralizing antibodies in spite of her negative HI, SRH, and CF tests. Two girls who did not respond to the first immunization, showed seroconversion after the second attempt. DISCUSSION In this study 99.15% of previously seronegative teenage girls gave positive rubella HI tests after immunization with RA/27/3 rubella vaccine. Of Table 5. Hi, CF, and SRH antibody titres in 5 serum samples from the 12 girls in group Ba Hi titre Haemolytic zone diameter (mm) CF titre Subject Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 BV 20 40 40 40 9.5 9.0 9.5 10.0 .4 .4 8 16 GM 20 160 40 40 8.0 11.0 9.5 10.0 .4 16 < 4 .4 IF 20 80 40 20 7.0 9.0 8.5 8.5 < 4 < 4 < 4 < 4 KAY 20 40 20 20 8.5 9.5 9.0 9.5 < 4 .4 4 4 LP 20 40 40 20 9.5 10.5 10.0 10.0 8 8 8 8 MJP 20 40 40 40 9.5 9.5 9.0 9.0 4 < 4 < 4 < 4 SJO 20 80 40 40 8.5 10.0 9.0 10.0 < 4 8 < 4 6 4 AJ 20 40 20 20 20 9.5 10.0 9.5 9.5 8.5 < 4 < 4 < 4 < 4 < 4 EEG 20 10 10 20 20 10.0 11.0 9.5 10.0 10.5 < 4 < 4 < 4 < 4 < 4 IH 20 40 20 40 20 7.0 9.5 8.0 9.0 9.0 < 4 4 < 4 4 4 MKS 20 10 10 10 10 9.0 8.5 8.5 8.5 7.5 .4 8 < 4 < 4 < 4 SS 20 40 20 40 20 8.0 9.5 9.0 9.5 9.0 .8 < 4 < 4 4 < 4 ° Sample 1 was taken before primary immunization against rubella; sample 2 was taken 6 weeks after primary immunization; sample 3 was taken one year after primary immunization; sample 4 was taken 6 weeks after re-immunization; sample 5 was taken after the rubella epidemic. 144 RUBELLA IMMUNIZATION IN ICELAND these vaccinees, only 9 (3/o) showed a significant decline in HI titre during the first year after immuniz- ation. It is known that the infection rate after rubella immunization depends on the type of vaccine used but is generally higher than that in persons with naturally acquired immunity. Other studies have shown that following the administration of RA/27/3 rubella vaccine, 2.207. (3) and 3.5 o (4) of vaccinees showed a significant rise in antibody titre 2 and 3 years, respec- tively, after primary immunization. In the present study, 1.5% of the vaccinees showed serological signs of infection in an epidemic occurring 2 years after immunization, compared with 1% of naturally immune subjects 3 - 5 years after their first rubella infection. Since 98.5%o of the vaccinees were pro- tected against rubella infection, as shown by the absence of a significant rise in rubella antibody titre in spite of close contact with patients, and since the HI titres showed little change after immunization, it is likely that rubella immunization confers a long- lasting protective immunity. It has been found (5, 6) that antibody titres after rubella immunization are generally lower than with naturally acquired immunity. In this study 12%o of vaccinees in group A had a post-epidemic HI anti- body titre of 20 or less 2 years after immunization. Of the 358 girls with naturally acquired immunity only the 12 girls in group B (3.4%o) had an HI titre of 20. After the epidemic, there were 13 low-positive girls in group B and the control group (6.307). Although it might be expected that the low-positive girls would be at the highest risk of reinfection, the poor results of re-immunization in this group, and the absence of increase in titres during the epidemic indi- cate that this may not be the case. It is noteworthy that only one of the infected girls, an unimmunized subject, had a pre-epidemic titre of 20. The others had HI titres of 40- 80. Of the 7 cases of serologically confirmed infection, 6 showed a significant rise in both CF and HI antibody levels. The seventh, an immunized girl, showed a rise in CF antibodies only, but she had a rubelliform exanthem indicating a clin- ical illness. Therefore, it seems to be difficult to predict who is likely to be infected when exposed to wild rubella virus. ACKNOWLEDGEMENTS The author is greatly indebted to Dr Stefan Adalsteinsson for help with the statistics, and to Sigridur Gudmundsd6ttir, Audur Antonsd6ttir, and Professor Margret Gudnad6ttir, of the Department of Microbiology, University of Iceland, for valuable help and advice during this work. RESUMt VACCINATION ANTIRUBEOLIQUE D'ADOLESCENTES EN ISLANDE ET SUIVI APRES UNE EPIDEMIE DE RUBEOLE SEVtRE Cette communication decrit les resultats de la vaccination antirubeolique pratiquee sur des jeunes filles seronegatives, Ag6es de 12 ans, A Reykjavik, Islande, en janvier-fevrier 1977. Le travail a comporte 1) une etude serologique des personnes vaccin6es pendant la premiere ann6e cons6cutive A la vaccination, alors qu'elles vivaient dans un environne- ment exempt de rub6ole, 2) les resultats de la vaccination de jeunes filles beneficiant d'une faible immunite naturelle, et ceux de la revaccination chez des vaccin&es A serologie faiblement positive, 3) un suivi apres une exposition massive des vaccin6es au virus sauvage de la rubeole au cours d'une epidemie severe qui s'est produite A Reykjavik au milieu de l'hiver 1978 - 79, deux ans apres la vaccination. Les cama- rades de classe non vaccin6es, chez lesquelles avaient e recherches les anticorps rubeoliques par inhibition de l'hemagglutination (IH) au d6but de ce travail, et dont on connaissait l'immunite naturelle, ont servi de groupe temoin dans la surveillance post-epid6mique. A l'origine, 730 ecolieres, que l'on savait avoir W expo- s&es A une seule epidemie de rub6ole, ont subi une recherche des anticorps rubeoliques IH et 372 d'entre elles (soit 50,9%) se sont revel&es seronegatives; 355 jeunes filles seronega- tives, et 12 ayant une faible immunit6 naturelle (titre 20 a l'IH) ont ete vaccin&es. Des prises de sang ont ete effec- tu6es six semaines et un an apres la vaccination. Ainsi, 336 paires de serum, 17 pr&lEvements uniques sur des jeunes- filles pr6c6demment seronegatives, et 12 paires de serum de vaccin6es A faible immunit6 naturelle ont ete recueillis en vue de l'etude des anticorps. Le taux de s6roconversion a ete de 99,15%. Seules trois jeunes filles seronegatives n'ont pas repondu A la vaccination par des titres d'anticorps mesu- rables par IH. Un an apres la vaccination, 94,8% des 344 vaccin&es 6tudi&es avaient, par la methode d'IH, un titre >40. Le titre d'anticorps IH est reste stable, et seuls 3% des 336 jeunes lilles vaccin6es, anterieurement s6ron6gatives, ont presente une chute notable du titre IH des anticorps au cours de la premiere ann6e. La moyenne geometrique de leur titre d'anticorps (MGT) 6tait de 62,07 au bout de six 145 146 B. RAFNAR semaines, et de 61,69 au bout d'un an apres la vaccination. Seules 3 des 12 jeunes filles examin&es (soit 25%) ayant une faible immunite naturelle ont montre a l'IH, une elevation sensible du titre des anticorps apres vaccination. Leur MGT etait de 40 six semaines apr6s la vaccination, mais est tomb6e A 25,20 au cours de la premiere ann&e. La revaccination n'a eu aucun effet dans ce groupe ni dans celui des jeunes filles precedemment seronegatives qui avaient faiblement repondu a la primo-vaccination. Au total, 345 vaccin&es et 193 de leurs camarades non vaccin&es mais anterieurement immunes ont ete etudi6es par IH, par fixation du compl6ment (FC) et par recherche des anticorps au moyen de l'hemolyse radiale simple (HRS) a la fin d'une epidemie de rubeole qui a eu lieu A Reykjavik deux ans apres la vaccination. Toutes ont e egalement exposees au virus rubeolique sauvage A l'ecole, ou des cas de rubeole se sont produits parmi des garsons non vaccines dans toutes les classes etudi6es. Au domicile de 116 (soit 33,6%) des vaccin6es et de 41 (soit 21,2%) de leurs camarades non vacci- n6es et naturellement immunis&es, des cas de rubeole se sont declares durant cette epid6mie. Malgre cette exposition massive, seulement 5 vaccin6es (1,5%), toutes seronegatives avant la vaccin,tion, et 2 jeunes filles non vaccin&es (soit 1%) ont manifest6 des signes serologiques de r6infection, et 2 de ces 5 vaccin&es ont presente un exantheme au cours de l'epidemie, mais sans autre trouble. Sur ces 7 jeunes filles, une seule, beneficiant d'une immunite naturelle, apparte- nait au groupe possedant de faibles titres d'anticorps, qui etait estime expose au risque le plus eleve de reinfection. Dans ces cas de reinfection, une vir6mie ne saurait etre exclue puisque 6 adolescentes ont revele une elevation du titre des anticorps tant FC que IH, et que la 7', en plus d'une elevation sensible des anticorps FC, a eu egalement un exantheme au cours de l'6pidemie. REFERENCES 1. EINARSD6TTIR, B. &. RAFNAR, B. Direct HIG-test for rubella antibodies. Journal of medical virology, 5: 303 - 308 (1980). 2. GRIST, N. S. ET AL. Diagnostic methods in clinical vir- ology, Oxford, Blackwell Scientific Publications, 1966, pp. 54-71. 3. GRILLNER, L. Immunity to intranasal challenge with rubella virus two years after vaccination. Comparison of three vaccines. Journal of infectious diseases, 133: 637-641 (1976). 4. FARQUHAR, J. D. Follow-up on rubella vaccination and experience with subclinical reinfection. Journal ofpedi- atrics, 81: 460 - 465 (1972). 5. HORSTMANN, D. M. Controlling rubella: problems and perspectives. Annals ofinternal medicine, 83: 412 - 417 (1975). 6. SCHLUEDERBERG, A. ET AL. Neutralizing and hemag- glutination inhibiting antibodies to rubella virus as indicators of protective immunity in vaccinees and naturally immune individuals. Journal ofinfectious dis- eases, 138: 877- 883 (1978).