Our retrospective study showed that almost all premature and/or low birth weight children hospitalized in the EHC neonatal department (97.7%) had completed the vaccination at 9 months. BCG and OPV 0 are routinely administered to preterm and low birth weight infants hospitalized in the EHC neonatal unit, which may explain the 100% completion rate for BCG and OPV 0 in our study. This confirms the results of the 2011 study by Denizot et al. in France, who found that the first vaccination before hospital discharge was associated with a better vaccination coverage rate .
We found that 81.6% of children were vaccinated at the age indicated in the EPI schedule, a figure almost twice as high as that found by Nakatudde et al. in 2019 in Uganda, which was 42.6%. Overall promptness in our study decreased with low gestational age (38.5% for those born before 32SA) and with low birth weight (33.3% for those with birth weight below 1500 g). This finding was also made in a recent study in the Netherlands by E. Rouers et al. who found a 60.5% promptness that dropped to 37% in children with gestational age < 28SA .
We observe that children born with low birth weight and gestational age far from term were more likely to have delayed vaccination. We found a very significant association between high prematurity, very low birth weight, low birth weight and not prompt vaccination. This confirms the finding of Maureen O'Leary et al in Ghana with low birth weight as a risk factor for poor immunization even for children born in health facilities .
Zero-dose oral polio vaccine (OPV) should be given at birth or as soon as possible thereafter to maximize seroconversion rates with subsequent doses and induce mucosal protection . In our study, we found 88.4% promptness for BCG and Polio 0 valences. Only 11.6% had received these vaccines at more than 7 days, which is lower than the figures from the study on reasons and determinants of delay of BCG vaccination in a community in sub-Saharan Africa by Bolajoko O Olusanya, in which 65.4% were vaccinated at 2 weeks, and 24.5% at 6 weeks . Nakatudde et al. found that in 2019 in Uganda, BCG was 92% prompt and OPV, 45.4% prompt, both received at birth . This disparity was due to stock-outs of OPV at Mulago Hospital in Uganda during the study period . In our study, we found similar readiness for BCG and OPV 0, indicating the availability of these vaccines in our health facility.
For diphtheria, tetanus, pertussis, polio, rotavirus, pneumococcus, and measles vaccines, we found > 90% readiness for DTPoqHepB/Hib, Polio (1st 2nd and 3rd contact), Rotarix (1st and 2nd contact), Amaril, and measles vaccines. These results are more than three times better than those of Pinquier et al. who found only 28 percent of preterm infants meeting the French recommendations for DTPoqHib, MMR, and HepB at age 2 .
In this setting, children born with low birth weight and those born at an early age began vaccination later than children born at term and/or birth weight ≥ 2500 g. The mean age of vaccination initiation was 6 days ± 11. This age is similar to that found in Ghana by Maureen O Leary et al . We found a significant association between birth weight and vaccination initiation (p < 0.001) with a mean vaccination initiation weight of 2233 g ± 494.
On the opposite, we did not find a significant association with maternal age, maternal education, occupation, religion, route of delivery, occurrence of adverse events, and maternal interest in vaccination. Our findings may contradict those of Ravi Prakash et al., who identified Muslim religion, maternal age < 20 years as a factor associated with low vaccine completion rates among preterm infants in India . They also found that maternal education (≥ 12 years of schooling) was a factor in satisfactory completion rates .
Distance from home to EHC greater than 5 km was associated with a high rate of no promptness compared with a distance of less than 5 km [OR: 3.48 (CI: 1.68–7.47, p = 0.001)]. This result is concordant with data posted by Maureen O'Leary et al. in 2017 in Ghana, who found that children living more than 5 km from the health facility were 1.37 times unvaccinated compared to those living 1 km from the health facility (p ≤ 0,0001) . This implies the need to educate mothers of preterm and low birth weight infants about the importance of continuing immunization at the health facility closest to home in case of difficulty in reaching the hospital where vaccination was started at birth.
Concerns about the safety of vaccines in preterm and low birth weight infants are often the reason for delayed vaccination, despite the fact that the frequency of adverse events appears to be comparable between preterm and term infants . Studies have shown that children with prior cardiorespiratory problems are at greater risk of developing these adverse reactions [19, 20]. In our study, 24.5% of children had an adverse reaction after vaccination, made of fever and local reactions (5.3%).