Final discussion 9 May 26 evening Among the 3972 children screened during the study period, 9.9% (393/3972) had vaccine delay. Of these, 43.3% (170/393) had vaccine delay due to non-medical causes. Previous studies from different parts of India have reported widely varying proportions of vaccine delay, ranging from 6.7% to 81.7%. Reported proportions include 19.5% from Uttarakhand, 33.7% from Kolkata, 81.7% from Haryana, 6.7% from Uttar Pradesh, and 45.4% and 69.6% from two different studies conducted in Maharashtra [8,16,19-24]. This wide variation may be attributed to differences in the study population, age groups included, operational definitions used for vaccine delay, and regional variations in immunization practices. Nevertheless, these findings suggest that vaccine delay varies considerably not only between states, but also within the same state. Vaccine delay has also been reported from several other countries, with proportions ranging from 9% to 65.7%, including Saudi Arabia (9%), Ghana (27.1%), Ethiopia (28.5%), and Iran (65.7%) [25-28]. These observations indicate that vaccine delay is a global public health concern affecting both developing and developed healthcare settings. In the present study, the proportion of vaccine delay varied across different vaccine age groups. The highest proportion of delay was observed for the 16-month vaccine, where 9.9% (45/453) of children experienced vaccine delay, while lower proportions were observed in other age groups. Similar findings have been reported in several Indian studies from Puducherry, Maharashtra, Haryana, Kolkata, and Uttar Pradesh, where delays were more commonly observed for vaccines administered at later ages [18,19,21-23,29]. Interestingly, both NFHS-4 and NFHS-5 surveys demonstrated similar patterns of higher vaccine delay among older children despite being conducted nearly 5–6 years apart, suggesting that this issue has persisted over time with little improvement [5,8]. A few possible reasons may explain this trend. One important factor could be the long interval between the 14-week vaccination visit and the subsequent measles-containing vaccine scheduled at 9 months of age. In addition, immunization cards often mention that the measles vaccine can be administered anytime between 9–12 months and that the subsequent DPT and measles booster doses can be taken anytime between 16–24 months. Such broader time windows and longer gaps between scheduled visits may contribute to forgetfulness and postponement of vaccination by caregivers. Forgetfulness has been identified as an important contributing factor in several studies from India and abroad, including studies from Kolkata and Ethiopia [21,27,30]. Many previous studies have reported that vaccine delay increases with higher birth order. Studies from NFHS-4 data, Maharashtra, Haryana, and Central India have demonstrated an association between higher birth order and delayed vaccination [8,16,19,21,22]. In the present study also, a similar trend was observed in the bivariate analysis, with vaccine delay increasing as birth order increased. However, in the multivariable logistic regression analysis, birth order showed only a borderline association with vaccine delay and did not reach statistical significance. This may be because, as the number of children in the family increases, the mother’s responsibilities towards the care of older siblings also increase, which may limit the attention given to timely vaccination of younger children. However, a study from Ghana reported contrasting findings, where first-born children were more likely to have incomplete vaccination [26]. Several studies have attempted to identify whether urban or rural residence influences vaccine delay, though the findings have been inconsistent. Studies from Himachal Pradesh, Chennai, and other urban settings in India reported higher vaccine delay and hesitancy among children from urban areas [14,31,32]. In contrast, studies from Ethiopia, multicountry analyses, Nigeria, and rural Indian settings observed greater delay among rural populations [23,33-35]. In the present study, however, no significant difference was observed between urban and rural children, both in the bivariate and multivariable analyses. Nowadays, the urban–rural divide is gradually narrowing in many communities because of improved transportation, communication, and healthcare accessibility. More than the place of residence itself, proximity and accessibility to vaccination centres may play a more important role in ensuring timely vaccination. This is supported by studies showing that children residing closer to PHCs or vaccination centres are more likely to receive vaccines on time [18,36,37]. Similarly, several studies from India, Ethiopia, and multicountry analyses have shown that vaccine delay is more common among children of illiterate or less educated parents and among families belonging to lower socioeconomic groups [8,16,23,33,38]. This is probably due to lower awareness regarding the importance of timely vaccination, misconceptions regarding vaccines, and limited access to healthcare information. Lack of awareness has also been identified as an important reason for vaccine delay in several studies conducted both in India and abroad [21,27,35,39]. On the other hand, a few studies from urban India and abroad have reported higher vaccine hesitancy and delay among educated parents and those belonging to higher socioeconomic groups [31,32,40]. Parents with higher education and income may be more likely to question the necessity of vaccines, fear adverse effects, or hesitate regarding newer vaccines and multiple vaccines given during the same visit. A study by Dhalaria et al. also reported higher delays among middle- and higher-income groups for certain vaccines [14]. However, in the present study, parental education and socioeconomic status were not significantly associated with vaccine delay in either the bivariate or multivariable analyses. Working mothers and parental busyness have also been identified as factors contributing to vaccine delay in studies from India and abroad [21,39,40]. This may be because working parents often find it difficult to take leave from work or adjust their schedules for vaccination visits. However, a study from Central India reported higher vaccine delay among homemakers compared to working women, suggesting that the relationship may be influenced by family support systems and caregiving responsibilities [16]. Gender differences in vaccine delay have also been reported in a few studies, with preference often being given to male children in certain settings. However, no significant association between the gender of the child and vaccine delay was observed in the present study, including in the multivariable logistic regression analysis. This may reflect improving awareness among parents, reduction in family size, and increasing emphasis on equal healthcare for both male and female children. Among the 16,777 live births during the study period, 82.9% of neonates received all birth vaccines within the recommended time period, while 16.3% had delayed administration of birth vaccines. Among neonates admitted to NICU, 10.4% received only the parenteral vaccines, whereas 0.7% received birth vaccines only at the 6-week visit, thereby missing the zero dose of OPV and the first dose of Hepatitis B vaccine during the neonatal period. In our hospital, sick or hemodynamically unstable neonates admitted to Level III NICU care are not planned for any birth vaccines during the acute phase of illness. Neonates who are clinically stable but still require NICU care receive only the parenteral vaccines, while oral vaccines are deferred temporarily and administered on the day of discharge. This practice is followed because of the potential risk of cross infection during the handling and care of multiple sick neonates in tertiary care settings. Being a tertiary care referral institute, a large proportion of high-risk deliveries, preterm births, and neonatal illnesses are managed in our hospital, which could explain the relatively higher proportion of delayed birth-dose vaccination. A study conducted in rural tertiary care centres and subdivisional health facilities in Sonepat, Haryana, reported that 28.9% of newborns did not receive birth-dose vaccines [41]. The barriers identified in that study included non-availability of vaccines in labour rooms, lack of vaccination services during night hours, inadequate skills among healthcare workers in administering intradermal BCG vaccine, and failure to supervise whether vaccines had been administered before discharge [41]. The study also observed that some parents requested early discharge, particularly following evening or night deliveries, because of cultural practices and family commitments. In contrast, in the present study, no eligible neonate missed birth vaccination because of healthcare system-related factors. Birth-dose vaccination services are provided almost every day in our hospital, and discharge procedures routinely include verification of vaccination status before the baby leaves the hospital. The missed or delayed doses observed in our setting were predominantly related to neonatal sickness and NICU admission rather than deficiencies in the healthcare delivery system. Minor illness in the child has been identified as an important reason for vaccine delay in several studies from India and abroad. A study by Narayanan et al. reported that 34.1% of caregivers cited minor illness in the child as a reason for delaying vaccination, while a study from Saudi Arabia observed that illness on the scheduled vaccination day was the most commonly reported reason for delay [32,40]. Similar findings have also been reported in studies from Maharashtra, Ethiopia, and other international settings, where child illness contributed significantly to delayed vaccination [19,27,38,39]. In many instances, caregivers may postpone vaccination because of concerns that vaccines could worsen the child’s illness or lead to additional adverse effects. Misconceptions regarding contraindications to vaccination during mild illnesses such as fever, upper respiratory tract infections, diarrhea, or cough may also contribute to unnecessary delays. In addition, healthcare providers themselves may occasionally advise postponement of vaccination during minor illnesses because of apprehension regarding adverse events following immunization. Sickness among family members may also indirectly contribute to vaccine delay by increasing parental responsibilities and limiting their ability to visit vaccination centres on scheduled dates. Although direct evidence regarding this factor is limited, studies have reported that parental busyness, competing household responsibilities, and caregiving burdens are important contributors to delayed vaccination [39]. Non-availability of vaccines has been reported as an important healthcare system-related factor contributing to vaccine delay in several studies from India and abroad. Studies from Maharashtra, Haryana, Ethiopia, Nigeria, and other international settings have identified vaccine stock-outs, non-availability of vaccines during certain hours, and fragmented immunization systems as major barriers to timely vaccination [19,26,35,37,41]. Similar observations have also been reported in studies from Africa and other low- and middle-income countries, where poor facility quality and interruptions in vaccine supply adversely affected immunization uptake [33,35,38]. A study from Sonepat, Haryana, particularly highlighted that non-availability of vaccines in labour rooms and absence of vaccination services during night deliveries contributed to missed birth-dose vaccination [41]. Likewise, studies from Ethiopia and South Africa reported that vaccine shortages and inconsistent vaccine availability were strongly associated with incomplete immunization [27,37]. However, in the present study, vaccine non-availability was not identified as a major reason for vaccine delay by either caregivers or healthcare providers. This may be because the study was conducted in a tertiary care teaching hospital with a relatively well-established vaccine supply chain and immunization services. Regular vaccine availability, dedicated immunization clinics, and continuous monitoring mechanisms in our institution may have minimized healthcare system-related barriers and ensured uninterrupted vaccination services. Family structure has also been evaluated as a possible factor influencing vaccine delay, although findings across studies have been inconsistent. Dasgupta et al. reported higher vaccine hesitancy among nuclear families, possibly because of limited family support and greater dependence on parents alone for childcare and healthcare-related decisions [15]. In contrast, a study from Central India reported higher vaccine delay among children belonging to joint families [21]. This may be because larger family size and multiple caregiving responsibilities in joint families can sometimes reduce attention towards timely vaccination schedules. However, in the present study, no significant association was observed between family type and vaccine delay. This suggests that family structure alone may not independently influence vaccination timeliness, and that other factors such as parental awareness, accessibility to healthcare facilities, family support systems, and competing responsibilities may play a more important role. Social media misinformation and false propaganda have emerged as important contributors to vaccine hesitancy and delay in recent years. Studies from Kerala and Puducherry reported that misinformation circulated through platforms such as WhatsApp, Facebook, and YouTube significantly influenced parental perceptions regarding vaccine safety and effectiveness, thereby contributing to vaccine resistance and hesitancy [17,29]. Similar findings have also been reported from other parts of South Asia, where the rapid spread of misinformation through social media platforms created fear, confusion, and mistrust among caregivers regarding childhood vaccination [33,40]. In many situations, unverified messages related to adverse