Timely vaccination with valid doses in a high coverage country, Oman

The dataset included 17,501 participants after excluding invalid and inconsistent records, exceeding the minimum required sample size. The distribution of clusters, households, and target children was consistent across all provinces. The households per cluster, children per household and average children in each cluster was around four, five and one respectively.

Almost all children (99.4%) had their immunization cards available during the survey. The majority of children surveyed (66.4%) were between 24 and 59 months old. The gender distribution was nearly equal, with 51.2% male and 48.8% female. Omani children represented 97.3% of the sample, while non-Omani children made up 2.7%. The mean and median age was 2.7 ± 1.3 years and 2.7 years respectively, with an age range from 4 months to 5 years.

The overall crude national vaccination coverage was nearly 100% and it varied from at birth 99.9–94.4% at 24 months as shown in Table 1. BCG and HBV vaccines showed the highest crude (99.9%) and valid (97.9%) coverage rates respectively, followed by the pentavalent vaccine and OPV (99.9% and 92.2%). The difference between crude and valid coverage suggests early or delayed vaccinations as children aged (Table 1). We observed high vaccination coverage across all age groups, with fully vaccinated coverage ranging from 99 to 96%. Overall, 98.7% of children under five fully vaccinated, 1.3% partially vaccinated, and only 0.01% remained unvaccinated. The detailed coverage analysis by governorate indicated that coverage for various vaccines was generally high (around 99%) across most governorates, with the exception of Dhofar and Muscat, which showed slightly lower coverage for vaccines targeted at the 12-24-month age group (89.3–98.7%). District wise coverage analysis was nearly uniform (98–100%) for the birth, six, and 12-month doses.

Table 1 Crude and valid dose immunization coverage

Figure 1 depicts the timeliness of vaccinations in the coverage survey. Majority of the vaccines at birth (98%), at 6 months (92.2%) and at 12 months of age (90.9%) were given within 30 days (timely vaccination) from the scheduled vaccination date. At later stages of children life, there was a delay in receiving vaccination at 18 months, which was nearly 11%. People who received vaccination very late (> 1 years from the scheduled date) was negligible (0.1–0.3%) at different stages of vaccination. Notably, delays in receiving vaccinations at 18 months were common across several governorates, with Thumriyat and Muqshin districts exhibiting the highest rates of late vaccinations, particularly for the 12 and 18-month doses.

In the study, 78% of the subjects received valid vaccinations, while 22% received invalid ones. Among partially immunized children, 63.5% had valid doses. Similarly, 78.1% of fully immunized children received valid doses, indicating that approximately 78% of fully vaccinated children had valid vaccinations (Table 2).

Table 2 Comparison of fully vaccinated with valid immunization

Figure 2 illustrates the distribution of invalid vaccinations by governorate/province in the coverage survey. The proportion of invalid vaccinations ranged from 3.3% at birth to 28.1% at 18 months of age. Among the governorates, North Sharqiyah recorded the lowest average rate of invalid vaccinations, while Dhofar reported the highest average rate.

Similar to governorates/provinces, as the age increases the invalid vaccinations increases in the districts/wilayats. The average invalid vaccinations ranged from 1.7 to 31.0% in Haima and Thumrayt respectively. Of the 61 districts, 31.1% (19/61) had average invalid vaccinations more than 10%. Four districts had average invalid vaccinations between 10 and 15% and five districts average invalid vaccinations 15–31% (Table 3).

Table 3 Average invalid vaccinations more 10% according to Governorate and district

Table 4 shows the dropout rate for various vaccines. It demonstrates that there is marginal increase in dropout rate as the age of the child increases from birth vaccine to the subsequent vaccination. Further, it noticed among 12–23 months’ children, there was 4.0% dropout from the birth dose (BCG, HBV) to 18 months’ dose MMR2, DTP & OPV Booster. Muscat and Dhofar identified as the areas with the highest number of missed doses, including a significant prevalence of multiple missed doses in these governorates. Moreover, Mehwat and Mazyoona districts recorded the highest dropout rates.

Table 4 Crude dropout rate for various vaccines for 12–23 months’ children

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