Background China maintains a high overall infant hepatitis B vaccination rate, but there are differences between premature and full-term infants. Premature infants have less physiologic reserve, less external adaptability to stressors, and often delayed vaccination compared to full-term infants - all of which may influence the immune protective effect of vaccination. Every year, 1.2 million premature babies are born in China. Timely vaccination with hepatitis B vaccine is the most effective measure to realize the goal of "zero infections" of hepatitis B virus in all newborns, but there are relatively few investigations of hepatitis B vaccination of preterm infants, leading to uncertainty of coverage and insufficient knowledge of factors influencing timely vaccination of this important population. Methods We obtained HepB vaccination histories for premature infants born between 2019 and 2021 in three provinces from the provincial immunization program information management systems.Extracted data included date of birth, sex, region, and dates of HepB vaccination. We conducted descriptive analyses that included basic characteristics of the study subjects, timely HepB1 vaccination, and full-series HepB vaccination.Factors influencing timely birth dose rated and full series vaccination rate were analyzed by logistic regression. Results There were 1623 premature infants that met inclusion criteria and were included in the final analytic data set. Timely HepB1 birth dose coverage was 71.41%. Premature infants born to mothers with unknown HBsAg status had a timely HepB1 birth dose rate of 69.57%. Timely HepB1 vaccination was higher at county level and above hospitals(72.02%) than hospitals below the county level(61.11%).The full-series HepB vaccination rate was 94.15%,but the full coverage rate of preterm infants weighing less than 2000g at birth was 76.92%.Logistic regression analysis of factors influencing timely HepB1 vaccination showed that the HepB1 timely vaccination rate was positively associated with being born to a HBsAg positive mother and being preterm with high birth weight, but was negative associated with being born to a mother with unknown HBsAg status. Regression analysis for factors influencing full-series HepB coverage showed that being born prematurely was positively associated, and being premature with a very low birth weight was negatively associated with full-series HepB coverage. Conclusions Timely HepB1 birth dose coverage in three provinces of China was less than the target of 90%,especially in the Premature infants born to mothers with unknown HBsAg status and at hospitals below the county level.Screening of pregnant women should be a universal normal standard. Hepatitis B vaccination training should be strengthened in hospitals to improve the timely HepB birth dose vaccination rate of premature infants and to effectively prevent mother-to-child transmission of hepatitis B virus.

The fused deposition modeling rapid prototyping system is based on the manufacturing principle of layer by layer. The sprayer is the key component which achieves the fused deposition process. Based on the polymer rheological property, the structure design and theoretical analysis of the mini-plunger sprayer of SW2502 fused deposition modeling system are studied. The plasticizing capacity of the mini-plunger sprayer is analyzed in theoretically. It’s very important for the fused deposition modeling process to maintain a stable plasticizing capacity. The driving force of ABS feed is related to several process parameters such as structure form of sprayer and material property, etc. The barrel and nozzle design should be fit for mobility, purity and mechanical property of ABS feed. The modified ABS feed adopts self-pressure-adding driving method to conquer the pressure losses of barrel and nozzle. The plasticizing capacity of the sprayer is more than 20g/h.