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Case Reports Indian Pediatrics 2001; 38: 280-283 |
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Prevalence of Rubella Antibody in School Going Girls |
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Rubella vaccine has emerged as the most effective public health measure against the well known crippling consequences of congenital rubella infection (CRI). After the devastating pandemic of rubella between 1962 and 1965, United States licensed the use of vaccine in 1969, which resulted in 99% reduction of cases(1). Encouraged by the dramatic success of the vaccine, the European Regional Committee of the WHO adopted the goal of "Elimination of Congenital Rubella Syndrome (CRS) by the year 2000 A.D." in the health for all program(2). The endemicity of rubella has been well established in India. However, no official data is available regarding the prevalence of acquired and congenital rubella infection as it is not a notifiable disease. About 50% of children acquire rubella antibodies by the age of 5 years and 80 to 90% become immune by 15 years(3). Studies from India and abroad have found that 10-20% women in child bearing age are susceptible to rubella(4-8). Between 6-12% of babies born with con-genital malformations or infections have serological evidence of rubella(9,10). Despite a safe and effective vaccine being available for more than two decades, in India so far there has been no clear-cut policy regarding rubella immunization of children either at 15 months or young girls at 9-12 years. Therefore, a prospective study was carried out to know the serological status of rubella in young girls and their response to vaccination.
In one hundred and forty healthy girls, aged 9-12 years, attending Pediatric Out-patient Department of Lok Nayak Hospital, a venous blood sample was withdrawn after an informed consent. Each girl was administered 0.5 ml of rubella vaccine containing 1000 TCID50 of RA 27/3 strain. The post vacci-nation samples were collected 6-8 weeks later and the girls were enquired for any side effects. The sera were separated and stored at –20°C and the paired samples were later tested simultaneously for the presence of rubella IgG antibodies. The results were interpreted as per the kit instructions. The seroconversion was the change from seronegative (<10EU/ml) to seropositive (>10 EU/ml). The patients who were seropositive before immunization and showed a further rise in antibody titres were also considered to respond to the vaccine. The antibody titres were also transformed into natural logarithms to calculate the geometric mean titres and results were analyzed using the Chi Square and paired ‘t’ tests.
The mean age of the girls was 10.7 years and 126 (90%) were seropositive whereas 14 (10%) were seronegative prior to immuniza-tion. Only 120 of the 140 girls came for follow up which included all the 14 pre-vaccination seronegative girls and they tested positive for rubella antibodies. Those with positive titres prior to immunization also showed a significant rise in the antibody levels (Table I). The mean antibody leavels before and after immunization were 306.1 EU/ml vs 569 EU/ml, respectively (p <0.001). No untoward effects of the vaccine were noticed.
The protection against rubella infection and CRS can be achieved through the following alternative choices of immunization: (i) Universal immunization of all preschool children against rubella with MMR vaccine; (ii) Selective immunization of pre-adolescent girls with rubella vaccine; or (iii) Combined immunization of all pre-school children, and susceptible adolescents and adults with MMR and rubella vaccine, respectively. Universal immunization interrupts the transmission of wild virus in the population and substantially reduces the endemic inci-dence rates of both acquired and congenital rubella infection. Although, it will not elimi-nate the problem of CRI immediately but with the extensive coverage of all preschool children, its beneficial effects will be clear and obtained in about 15-20 years when these children enter the child bearing age(11). Selective immunization, on the other hand, reduces the risk of CRI among immuni-zed women and encourages the acquisition of immunity by natural infection during early childhood and further boosts the vaccine-induced antibody by the circulating virus. This is perhaps of advantage in situations where MMR is not being given in early childhood. It has been observed that vaccinating children at 15-18 months requires mainte-nance of protective levels of antibodies for 20-25 years. If universal immunization is incompletely implemented, it may increase susceptibility among the post-pubertal popu-lation with a consequent increase in the occurrence of CRI(11). Therefore, the best results can be achieved only by combined immunization policy as adopted by Denmark, Sweden, most of the European countries and USA where the first dose is offered as MMR vaccine at 15-18 months of age and the second dose as MMR vaccine at 6-12 years or only rubella vaccine exclusively to girls at 12-14 years of age. In the present study, 10% (14/140) girls were found to be seronegative which is similar to the observations from studies in India and abroad(4,12). All the 14 sero-negative girls had seroconverted following immunization showing a good seroconversion rate. Plotkin had observed a seroconversion rate of 100%(13). Also, all the vaccinees with the preimmunization positive antibody titres did not register a fall in the titre levels but had a post vaccination rise in the titres (Table 1). Transplacentally acquired maternal antibody (passive antibody) is known to interfere with immune response to vaccine but the anti-bodies in 9-12 years old are due to active antibody production following a previous unrecognized infection. It is known that vaccination in such individuals results in secondary immune response rather than having any inhibitory action and such subjects are likely to show a rising titre(14). The prevaccination titres were significantly lower than in postvaccination samples (p <0.001). The vaccine did not produce any side effects like fever, rash, lymphadenopathy, thrombo-cytopenia, arthralgia or transient arthritis as reported more often in susceptible adolescents and adults, especially females(1).
Contributors: SY conceived the study, its design and the analysis and interpretation; she will act as the guarantor for the manuscript. VW was responsible for collection of data, its analysis, review of litera-ture and interpretation. AC supervised laboratory investigations.
Funding:
Serum Institute of India Pvt. Ltd.
provided the kits and vaccine.
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