Indian Academy of Pediatrics (IAP) has been recommending MMR vaccine since many years, initially in 2-dose schedule and now 3-dose schedule (9-12, 15-24 and 5 years) [4,5]. There is limited published literature from our country to support many of these recommendations [6]. In view of paucity of data regarding need for 2nd dose of MMR vaccine for Indian children, we planned this study to find out seropositivity rates – at 4-6 and 9-12 years of age – among those who received one-dose measles at 9 months of age and one-dose MMR at 15 months of age.

This seroprevalence study was carried out in the outpatient department (OPD) of a tertiary-care referral hospital in Chandigarh, Northern India over a period of one year (April 2013 – March 2014). Ethical clearance was obtained from Institute ethics committee before commencement of the study. Consecutive children at either 4-6 or 9-12 years of age, attending pediatric OPD for vaccination were screened. Only those having documentary evidence (immunization card) of having received measles vaccine at 9-12 months and MMR vaccine at 15-18 months were included. An informed written consent from their parents was obtained. Children receiving prolonged steroid therapy (>4 weeks) in past six months, those having a history of administration of blood or immunoglobulin in last three months, and those diagnosed with malignancy or immunodeficiency were excluded from the study. The primary objective was to find out the percentage of children having antibodies against measles, mumps, and rubella in seroprotective range; and secondary objective was to find out geometric mean concentration (GMC) of these IgG antibodies.

A detailed history regarding previous vaccinations and other relevant information was elicited from their parents using a pre-structured proforma, and 2-3 mL of venous blood was drawn from the enrolled subject by venipuncture. The antibody titers were estimated using ELISA IgG quantitative kits for measles (VIRO-IMMUN Labor-Diagnostika GmbH, Germany), mumps (IMMUNOLAB GmbH, Kassel, Germany) and rubella (DIA.PRO Diagnostic Biprobes SRL, Milano, Italy). Antibody levels above 0.3 IU/mL for measles, above 12 U/mL for mumps, and above 10 IU/mL for rubella were considered seropositive, as per manufacturer’s recommendations [7-9]. The results of the study and their antibody titers against measles, mumps, and rubella, were informed to enrolled children and their parents. One additional dose of MMR vaccine was advised for children whose titers were below the seroprotective range.

Out of total 80 children enrolled, 50 (37 boys) were in group-1 (4-6 years) and 30 (16 boys) in group-2 (9-12 years). The mean age at recruitment in group-1 was 61 months, and in group-2 was 125 months.

Majority of study children in both groups had antibodies in seroprotective range for all three disease (Table I). Geometric mean concentration (GMC) of IgG antibodies (IU/mL) increased from those seen at 4-6 yrs than at 9-12 yrs age for measles, mumps and rubella.

TABLE I	Antibodies (IgG) Against Measles, Mumps and Rubella in Study Children

Our study showed seropositivity rates against measles, mumps, rubella to be 80%, 86%, 96% at 4-6 years and 83.3%, 96.7%, 96.7% at 9-12 years of age, respectively among studied population. In a similar study from Delhi, Gomber, et al. [10] reported seropositivity of 21.4%, 87.4%, 75.7%, respectively at age of 4-6 years, after receiving one dose MMR vaccine at 15 months of age. Raut, et al. [11] showed these titers to be 83%, 95%, and 100%, respectively, after six years of one dose of MMR in children aged 5-10 years [11]. Similar studies from other developing countries have seropositivity rates varied from 76-92%, 66-75%, 56-90%, respectively [12-15]. We did not come across studies reporting titers at the age of 10 years.

The number of susceptible subjects among population should be kept <5% to achieve and maintain measles control [9]. In our study, measles seroprevalence rates acquired by two dose measles containing vaccine (9 and 15 months) were lower than expected (80% and 83.3%). If the findings of suboptimal response remain consistent in other studies too, we may require an additional dose of measles-containing vaccine at a later age to make measles elimination possible. The current MR campaign could help in filling this immunity gap. The percentage seropositivity for Rubella in our study indicates good amount of protection offered by MMR when given at 15 months of age; the quantum of this protection during child-bearing age will decide whether there is a need for repeat MMR.

The results of our study have to be viewed in context of its limitations. Our sample was small, and can be considered as a pilot to plan larger population-based studies. It was a hospital-based study, and it may not reflect the situation in communities. The results of our study are preliminary, but indicate that a single dose of MMR vaccine provide good seropositivity results against rubella till 10 years of age. However, a seropositivity rate against measles antibodies is low despite two doses of the vaccine. Similarly, immunity against mumps also may have to be boosted in older children.

Contributors: SV, HP, NS: conceptualization of study; HP collected the data; HP,SV,BB: were involved in management of cases; AR: provided the laboratory support for detailed investigation of cases; SV: monitored and reviewed the data periodically; SV, HP, BB: reviewed the literature and drafted the manuscript; All authors approved the final draft of manuscript.

Funding: None; Competing Interest: None stated.

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