**3. Results**

Between 1 January 2019, to 31 December 2022, a total of 6,235,305 children were enrolled in the SEIR from the 2019 (23.29%), 2020 (25.35%), 2021 (25.62%), and 2022 (25.73%) birth cohorts. The proportion of males enrolled in the SEIR, as compared to females, was consistently higher across all birth cohorts (2019: 52.11%, 2020: 52.14%; 2021: 52.30%; 2022: 52.25%) (data not shown).

Across districts, we found a distinctive pattern in districts Kashmore, Ghotki, Jacobabad, and Tharparkar, having the highest adjusted median M:F ratios at enrollment: (Kashmore: 1.11 (IQR: 1.04–1.25); Ghotki: 1.11 (IQR: 1.04–1.16); Jacobabad: 1.07 (IQR: 1.00–1.13), and Tharparkar: 1.12 (IQR: 1.02–1.18)) (Table 1). The findings were similar for Penta-1, Penta-3, and Measles-1 vaccinations. A consistent trend, therefore, emerged, showing females falling behind males consistently in these districts from enrollment into the SEIR until their Measles-1 vaccination. At the UC-level, a high median M:F ratio emerged for selected UCs in District Thatta, where thrice the number of males were vaccinated, as compared to females.

When examining the GIR, we observed that once children were enrolled in the SEIR, coverage rates for vaccines were similar for females and males, as shown by the UC-level median GIR for Penta-1 (median: 1.00, IQR: 1.00–1.01), Penta-3 (median: 1.00, IQR: 0.99–1.01), and Measles-1 (median: 1.00, IQR: 0.99–1.01) (Supplementary Table S1).

Tracking the M:F ratios for vaccines over the 4 years showed high inequities in the number of females vaccinated, as compared to males, in 2019 for Penta-3 (1.14, range: 0.24–8.00) and Measles-1 (1.14, range: 0.14–5.00), which declined to 1.10 (Penta-3 range: 0.49–5.00; Measles-1 range: 0.25–2.07) in 2020 and remained at the same level for the following 2 years. The M:F ratios for Penta-1 remained roughly the same between 2019 and 2022, showing no major progress was made in reducing these disparities over the last 4 years (Supplementary Figure S2). The GIR reflected a similar picture of slightly higher inequalities in coverage among the enrolled children in 2019. Thereafter, coverage rates became more balanced between females and males (GIR: 1.00) for all the vaccines in 2020–2022 (Supplementary Figure S3). At the UC level, we found that 11.6% (131/1129) of the UCs showed a M:F > 1.10 for Penta-1 consistently over the four years. This proportion was 10.7% (121/1129) for Penta-3 and 8.9% (101/1129) for Measles-1, reflecting certain geographic pockets had persistently higher numbers of males being vaccinated, as compared to females, year-on-year (Supplementary Table S3). A closer geographic examination revealed that these UCs were spread throughout the province, as opposed to being located in clusters (Supplementary Figure S4).

The up-to-date coverages at specific age intervals for Penta-1, Penta-3, and Measles-1 showed more males were vaccinated, as compared to females, at each age (M:F ≥ 1.10) (Figure 1).

Among the enrolled children, 1 out of every 2 UCs in the province had females falling behind males on timely vaccinations of Penta-1, Penta-3, and Measles-1, as denoted by GIRs > 1.00. Notably, 60.7% (685/1129), 57.4% (648/1129), and 54.5% (615/1128) of UCs had GIRs > 1.00 for up-to-date coverage of Penta-1 at 10 weeks, Penta-3 at 18 weeks, and Measles-1 at 10 months. This proportion continued to decline across ages, demonstrating a narrowing of the inequity gap at the UC level as children aged (Figure 2).

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**Figure 1.** Male-to-female ratios of up-to-date vaccination coverage of Pentavalent-1 at 10 weeks and 6, 12, 18, and 24 months; Pentavalent-3 at 18 weeks and 6, 12, 18, and 24 months; and Measles-1 at 10, 6, 12, 18, and 24 months, in 0–23-month-old children in 2019–2022 birth cohorts enrolled in SEIR (1 January 2019–31 December 2022).

By observing the inequities in enrollment and the number of vaccinated males and females across maternal literacy levels, we found higher inequities among children with mothers who had only primary education (1–5 years of education), as compared to mothers with higher education levels and those who were not educated at all (Table 2). This was evident for Penta-1 (median M:F ratio: 1.09 (IQR: 0.92–1.3)), Penta-3 (median: 1.10 (IQR: 0.91–1.33)), and Measles-1 (median: 1.10 (IQR: 0.93–1.33)). With increasing education levels, the inequities were reduced, as shown by the median M:F ratio declining to 1.00. However, when examining the inequities at the UC level, individual UCs had high inequities in enrollment and the number of vaccinated males vs. females (M:F ratio between 7.00–10.00), even when mothers had high literacy levels (≥11 years of education).

**Figure 2.** Gender inequality ratio (GIR) at up-to-date vaccination coverage of Pentavalent-1 at 10 weeks and 6, 12, 18, and 24 months; Pentavalent-3 at 18 weeks and 6, 12, 18, and 24 months; and Measles-1 at 10, 6, 12, 18, and 24 months, in 0–23-month-old children in 2019–2022 birth cohorts enrolled in SEIR (1 January 2019–31 December 2022).

Rural UCs had higher median M:F ratios, as compared to urban UCs, for Penta-1 (median M:F ratio 1.11 vs. 1.06), Penta-3 (M:F ratio: 1.11 vs. 1.06), and Measles-1 vaccinations (M:F ratio: 1.10 vs. 1.07). The UC-level ranges, however, demonstrated that there were selected UCs with as many as five times more males being vaccinated than females for Measles-1, even in urban areas. Within the rural UCs, the remote-rural UCs reflected worse equity outcomes, with median M:F ratios as high as 1.14 for Penta-1. The slum UCs had the worst median M:F ratios for Penta-1 (1.07 (IQR: 1.03–1.11)), Penta-3 (1.07 (IQR: 1.03–1.12)), and Measles-1 (1.07 (IQR: 1.03–1.12)), as compared to non-slum UCs (Penta-1: 1.05 (IQR: 1.01–1.09), Penta-3: 1.05 (IQR: 1.02–1.09), and Measles-1 1.06 (IQR: 1.01–1.09).

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Based on M:F ratios by mode of vaccination, we found marginally higher inequities in the number of males vaccinated, as compared to females, among vaccinations conducted at fixed immunization centers, as compared to immunizations by routine outreach (Penta-1: 1.09 vs. 1.08; Measles-1: 1.09 vs. 1.08)). Lower median M:F ratios were found for immunizations administered by EOAs, (Penta-1: 1.07; Penta-3: 1.07; and Measles-1: 1.07), showing more equity between the number of females and males vaccinated during the intensive periods of EOAs conducted in the province.

Slight variations in M:F ratios were also observed when investigating inequities across UCs with varying numbers of female and male vaccinators. No differences between the number of males and females vaccinated (across any antigen) were observed when examining the median M:F ratios. However, we observed slightly increased inequities at the UC level in areas where there were no female vaccinators (UC range: 0.80–3.00 for Penta-1 and 0.80–2.80 for Penta-3 and Measles-1). We noted that even in areas where there were more female than male vaccinators (selected UCs in Karachi Division, Supplementary Figure S5), there were UCs that still had fewer females vaccinated than males (UC range: 1.00–1.20).

Conducting the above analysis according to the GIR did not reveal substantial inequalities in coverage rates between males and females (median GIR of UCs ranged between 0.99–1.03). Selected UCs demonstrated high inequalities. Nevertheless, a clear correlational pattern between inequality in coverage and maternal literacy, geographic location, modality of vaccination, and sex ratio of vaccinators, was not always obvious (Supplementary Table S2).
