Study of appropriate timing and short term effectiveness of measles vaccination

Introduction: Measles remains the leading cause of vaccine preventable childhood mortality and morbidity in developing countries. Measles vaccine contributes to the reduction of childhood mortality. The optimal age of vaccination has to be individualised for each country. Materials and Methods: The study was done for a period of two months in a government hospital Davangere. A total of 84 children were studied in three groups. Group 1 comprised of 29 children, of 9 months (± 10 days) of age, not vaccinated against measles. Group 2 of 28 children of 18 months (± 15 days) of age, vaccinated against measles at 9 months of age. Group 3 of 27 children of 36 months (± 15 days) of age, vaccinated against measles (EZ strain) at nine months of age. Antibody titres more than 200mIU/ml, was considered seropositive and statistical analysis was done by ANOVA and Mann Whitney test, chi square test. Results: In group 1, 13 (45%) of 29 children were seropositive, 55% were seronegative, and 8 (28%) had antibody level above 1000 m IU/ml. In group 2, 7(26%) were seronegative. In group 3, 5(18%) were seronegative. Antibody titres had significant statistical variation between groups 1 and 2, and groups 1 and 3. Sex, nutrition status and duration of exclusive breast feeding did not have any influence in the seropositivity in all the three age groups. Conclusion: Measles vaccine should be administered before 9 months, as early as 6 months and second dose at 12-15 months of age.


Introduction
Measles is a vaccine preventable cause of childhood mortality and morbidity. World has turned its attention towards measles eradication next to small pox, polio.The main reasons for this can be attributed to the decreased vaccination coverage, use of low potency vaccines and low availability of resources. Very few studies are there in world [1][2][3][4][5][6]. In India reported case of measles represents only the tip of iceberg. It requires the identification of distribution and ages of susceptibility of children. There are very few Indian studies [7][8][9]. This study is an attempt to evaluate the appropriateness of the current measles vaccination policy in practice in our country, by estimating quantitatively measles IgG antibodies at three different age groups on the eve, when the world is eagerly waiting for the announcement of measles eradication strategy by world health organization. The objective of present study was to know the appropriateness of the timing of measles vaccination as practiced by universal immunization programme in India and to find out about the short term protection offered against measles by the current vaccination practice.

Material and Methods
Children attending outpatient department and the immunization clinic conducted at Women and Child Health Hospital at Davangere which is attached to JJM Medical College. Study period of 2 months.

Study design and inclusion criteria:
The study was a cross sectional examination of measles IgG antibody levels in children of three age groups. 1. Group 1 of 29 children, of 9 months (± 10 days) of age, not vaccinated against measles.

Results
Total of 84 children were studied in three groups.
Group 1: 29 nine month old children, not vaccinated against measles. Out of whom 15 were males and 14 were females Group 2: 27 eighteen month old children vaccinated against measles at nine months of age.out of whom, 11 were males and 16 females Group 3: 28, thirty six month old children vaccinated against measles at nine months of age.whom 16 were male, 12 were female Almost all the children of the study group belonged to low socio-economic status as per modified Prasad classification.
There is no variation in the socio economic status between the study groups (Fig 1). Results of Measles IgG antibody levels are shown in Table 1. There is significant variation in the first group compared to second and third groups, but, the difference in seropositivity observed between second and third groups (74% and 82% respectively) is not statistically significant.
Measles IgG levels observed in three different groups were compared simultaneously using one way ANOVA. Table 3. This showed statistically significant variation (p-value<0.01) between the three groups. IgG levels between two groups each compared using Mann-Whitney test showed significant difference in group 1 compared to group 2 and 3 table 4. The observed variation in IgG levels between groups 2 and 3 is not statistically significant. Measles antibody level compared between children with normal nutritional status according to IAP classification with that of those with grade l and grade 2 protein energy malnutrition (PEM) using Chi-square test showed no statistically significant difference. Comparison of seropositivity between the same using Fisher's exact tests also did not show significant variation as shown in table 6 Duration of exclusive breast feeding and seropositivity were compared all the three age groups using fisher's exact test, there was no significant variation in any of the groups as shown in table 7        In the second study group of children of 18 months, who were vaccinated at 9 months, 26% were seronegative. 19% had levels above 5000mIU/ml, which points towards subclinical infection, hence second measles vaccine should be made mandatory at a period 6 months after vaccination. Damien et al estimated the susceptibility to asymptomatic secondary immune respone against measles in vaccinated and late convalescent persons to be 22.2% to 33.2% and 3.2 to 3.9% [6]. Seronegativity could also be due to vaccine failure [ 7,8,9,10,11].
In Group 3 children, 82% were seropositive. There was no statistical significant variation of seropositivity between 18 and 36 months old children. 18% were seronegative at 36 months, indicating less protection level, emphasizing the need for second dose of vaccination [12,13,14].

Conclusion
Our data suggests revision of existing measles vaccination policies from the existing single dose vaccination at 9 months to a two dose schedule, the first as early as 6 months and the second at 12-15 months of age.