This was a community-based cross-sectional study and conducted in rural and urban districts of Kassala locality in Kassala State, Eastern Sudan in November 2022. The State covers an area of 42,282 km² with a population of approximately 2.5 million inhabitants. It is located in the eastern part of Sudan, bordered by the states of Eritrea and Ethiopia. It is subdivided into 11 localities. Most populations practice grazing in addition to agriculture.

The study population includes parents of at least one child aged (6–35 months). Either mothers or fathers were eligible for participation. Parents were asked to report about only one child to reduce the risk of recall bias. If there was more than one child in the same age range in the family, the parents/guardians were asked to report about only the youngest one. If both mother and father were available, they were asked to nominate one of themselves to complete the questionnaire.

To ensure that people from various socio-cultural and socioeconomic backgrounds (i.e., education and wealth level) are included in this study, we collected data from parents/guardians in two different rural and urban districts in Kassala; Tajouj village, and Alkhatmia district. Parents were selected in each district using consecutive sampling (convenience sample), as every parent meeting the criteria of inclusion (i.e., had a child in the age range) was included in the study until the required sample size was achieved from each district. The minimum sample size was estimated at 384. To cover for possible drop-out due to refusal to answer some crucial questions, a total of 400 parents were selected for the study (i.e., 200 per district). The sample size was computed using the following formula:[n=z2pqd2]Where, n = sample size. z = (1 - α), is the z-score corresponding to a 95% confidence interval and was computed as 1.96. p = Expected probability of pentavalent vaccination coverage in the rural areas in Kassala, which is unknown, therefore it was estimated at 50%. q = (1- p) or 50%. d = desired margin of error or 0.05.

Data were collected using the Behavioral and Social Drivers of Vaccination (BeSD) survey (26), which was translated to Arabic, and adapted and pre-tested in the local context. This survey, developed by the WHO, measures four underlying factors: thoughts and feelings, social processes, motivation, and practical issues. The question about perception toward gender-biased vaccination was adapted from a question about decision-making autonomy for vaccination in the (BeSD) survey. The questionnaire was interviewer-administered. The questionnaire for the study included parent's socio-demographic characteristics, child characteristics, mother's educational level, household income (was measured as self-ranking), and perception towards gender-biased vaccination, which were used as independent variables. The uptake of the pentavalent vaccine was used as the dependent variable, which was measured as fully immunized (being vaccinated with three doses), partially immunized (being vaccinated with one or two doses) and not immunized who have not received any dose of pentavalent.

Data analysis was performed using Statistical Package for Social Sciences (SPSS) software (Version 26). The Chi-square or Fisher's exact (when the count is <5 in a cell) test was conducted to assess the factors associated with under-immunization among children. We focused on under-immunization rather than non-vaccination because we found that the proportion of under-immunized children is 14%, which is much higher than the proportion of unvaccinated children (2%). We excluded from the Chi-square test those who were not vaccinated, didn't know their vaccination status and missing data (e.g., Mother's education). A p-value of <0.05 is considered statistically significant.

Ethical approval was obtained from the Ahfad University for Women Ethical Committee (IRB). Permission to enter the communities was obtained from the community leaders in the rural districts. Written and/or verbal informed consent was obtained from each participant.

As shown in Table 1, a total of 400 parents of children aged 6–35 months were interviewed with 100% response rate. Half of them (50.0%) are from the urban district. The majority of the participants (91.8%) were mothers, and (92.5%) of them were not employed. The mean age of mothers was 27.6 (SD = 5.36). We surveyed the parents about the level of education of the mothers; results revealed that over half of the mothers (54.7%) had attended primary school, while 19.5% had never attended school. Concerning marital status, the vast majority (95.2%) of the parents are currently married. Half of the participants (50.2%) self-ranked their household income as medium. About half of the households (53.0%) have only one child under the age of five, followed by 38.3% of households having 2 children. Of the children whose vaccination status was recorded, 52.8% were male.

Figure 1 shows that the majority of the children (83%) were fully vaccinated with the pentavalent vaccine (i.e., 3 doses), while 14% were vaccinated with either one or two doses (Partially immunized) and 2% were not vaccinated.

Figure 2 shows that about 1 in 5 participants (19.3%) perceived male vaccination as more important than female vaccination. We did further analysis to assess the association between perceiving male vaccination as more important than female vaccination and the socio-economic status of the parents, including their residence (i.e., rural or urban) and their income level, but there were no significant associations.

Table 2 shows that socioeconomic factors, including mothers’ education (p = 0.001) and household income level (p = 0.026) were significantly associated with children's vaccination status. Mothers with primary education were more likely to partially vaccinate their children with the pentavalent vaccine, followed by secondary, and non-educated mothers. Those who self-ranked their household's income as low or very low were more likely to have under-immunized children.

Furthermore, the parental perception of the importance of male vaccination showed a significant association with children's vaccination status (p < 0.049). Parents who perceived male vaccination as more important than female vaccination are more likely to partially vaccinate their children.

There were no significant associations between vaccination status and the residence of the household, the number of children, or the sex of the child whose vaccination status was recorded.

We acknowledge some limitations related to our study; therefore, the study's findings should be interpreted within the context of this study. One of the limitations of this study is that there was unintentional selection bias due to consecutive sampling to recruit participants until the pre-determined sample size was reached from both districts. Additionally, from a gender perspective, most of the participants were female; this may be attributed to the time when the interviews were conducted (i.e., men at work). It was observed that fathers’ perceptions, perspectives, and decision-making roles regarding vaccination were missing due to their absence during the study. However, in Sudanese culture, like many other African countries, mothers are primarily responsible for the health and well-being of their children and family and, hence, have a better understanding of the health situation (33). Therefore, some parents preferred that the study should include mothers rather than fathers. We suggested future research to explore the perspectives of a broader range of parents, including fathers.

Given the study's purpose of shedding light on the role of gender norms on vaccination and its possible impact on children's vaccination, we performed only the chi-square test to examine the relationship between independent variables and the dependent variable. However, we did not go further in doing a logistic regression, which could be helpful in analyzing categorical variables and better understanding the predictors of immunization status.