Inclusion criteria were fulfilled by 1401 amongst 4196 indoor admissions. Seventeen children less than 8 weeks of age were excluded (not yet beyond time when eligible). Thus, 1384 children were analyzed (60.5% males). The mean age was 100.7 ±88 weeks (range 3.7-312.9 weeks). At least one vaccine was received by 1296 (93.6%), 88 (6.4%) were unimmunized and 1050 (76%) children were fully immunized (UIP schedule) [877 (63.5%) age appropriate immunization, 173 (12.5%) up to date but not age appropriately immunized]. The immunization status is presented in Fig.1.

Fig. 1 Immunization status of the study population.

Under-vaccination was observed in 24% of children (334). MOI accounting for 79.6% of under-vaccination was present in 266 (19.2%). Almost all MOI (98.5%) were unacknowledged. Sixty-eight cases (4.9%) were under-vaccinated but without a MOI. For a child with MOI, if each vaccine missed was considered as a missed opportunity, then 1243 vaccinations were missed (4.67 missed vaccinations child). If each visit when vaccination was missed was considered a missed opportunity, 702 visits were associated with MOI (2.64 missed opportunities child).

Median age at vaccination and the difference between recommended and actual age of vaccination could be determined in 96 children with MOI having records with date of vaccination (Table I). Of 2473.1 weeks of under-vaccination, MOI accounted for 2299 weeks. The proportion of under-vaccination weeks attributable to MOI was 92.9%.

The demographic parameters of children with MOI (n=266) were comparable to those who were under-vaccinated (n=68) in terms of gender, religion, birth order, residence, maternal age, and socio-economic status. MOI occurred during a visit for an acute illness in 80.5% of cases, for a chronic disease in 18.8% and a well child visit in 0.7%. The type of health facility visited was general practice (45.5%), medical college (23%), practicing pediatrician (15.4%), public health facility (6%), private institution (8.6%) and an alternative medical practice (1.5%). The qualification of the health care provider was MBBS (50.4%), post-graduate degree in Pediatrics (43.6%), degree in alternative medicine (3.4%) and super-specialty or non-Pediatric degree (2.6%). The reasons for MOI were immunization history not reviewed (94%), false contraindication (2.2%), wrong immunization history (1.5%), physician not advising immunization (1.1%), unavailability of immunization card (0.7%), and visit not on ‘immunization day’ (0.5%).

MOI occurred significantly more often with home delivery, incomplete or incorrect maternal knowledge of immunization, and general practice and non-Pediatric/ non-Medical college based practice [odds ratios: 5.1 (95% CI 2.3, 11.0), 4.8 (95% CI 1.2, 18.5) and 4.0 (95% CI 1.9, 8.3), respectively]. Testing with Hosmer and Lemeshow goodness of fit test indicated fitness of data in the model.

The present study documents that 80% of under-vaccination and 93% of under-vaccination time was due to MOI, occurring during acute illness visits. Almost all MOI were unacknowledged, attributable to oversight on the part of the health care provider in obtaining history of immunization in 94% of cases. This underscores the necessity of implementing interventions in office practice to reduce MOI including screening a child for eligibility at every preventive or curative visit, a tracking system to alert the physician when immunization is due, recording dates of immunization, and ensuring caregivers carry the immunization card at every visit [2]. Similarly, every hospital admission must be exploited as an opportunity to immunize the eligible or advise the due vaccine at discharge.

Previous studies have implicated provider misconceptions like avoiding immunization during minor illness as a significant predictor for MOI [6]. Though illness characteristic was not significantly predictive of MOI in this study, the likelihood of MOI was higher with visits to non-Pediatric/non-Medical college based practice including General Practitioners. This is relevant as a large proportion of health care delivery in India is by General Practitioner, who often are the first and only contact for patients [7, 8]. Their correct compliance with the National vaccination policy is critical for its success. Our study draws attention to the urgency of corrective measures to encourage desirable immunization practices such as simultaneous vaccination, safety of vaccination during mild acute illness and knowledge of true contraindications amongst other practitioners [2].

Earlier studies have documented that maternal knowledge about vaccines and contraindications for immunization was sub-optimal [9-11]. Many harbored erroneous beliefs and misconceptions, especially about vaccinating during acute illness [6, 9-14]. However, maternal acceptability of immunization was documented to be high in those with MOI [3]. Therefore education about the diseases being targeted, nature and timing of vaccines, their benefits and adverse effects, and acceptance of immunization during minor febrile illnesses will be critical to empower mothers to demand vaccination and reduce drop-out [6,11-13,15].

In conclusion, MOI can be tackled by accomplishing the National population policy target of 80% institutional deliveries [16], empowering mothers to demand immunization [6,9,17] and ensuring optimum immunization delivery by general practitioners. Periodic surveys for MOI should be a performance indicator for delivery and utilization of immunization services in the country [2,19].

Acknowledgment: The authors thank Dr Sanjay Oak, Director (Medical Educations and Major Hospitals, Municipal Corporation of Greater Mumbai) and Dean of Seth GS Medical College and KEM Hospital for granting permission to publish the paper.

Contributors: MNM designed the study, supervised the data collection and analysis, and wrote the manuscript. MNM will act as guarantor of the paper. CM collected and analyzed the data and prepared the draft. AP performed the statistical analysis and helped in drafting the manuscript.

Funding: None.

Competing interests: None stated.