Factors associated with hepatitis B virus immunization coverage at the beginning of a population campaign in the Lazio region, Italy

Background: The hepatitis B virus (HBV) vaccination was introduced in Italy in 1991 as compulsory among newborns and among 11-year-old children.

Methods: We conducted a retrospective study to evaluate the HBV immunization coverage of the two target populations by the public health services in the Lazio region and to analyze factors associated with starting and completing HBV immunization in the initial period of the campaign. We used data registered in the public health services of 7/51 Health Districts. As a proxy indicator of services' performance we used the "expected immunization period," that is, the 6-month period in which each child should have been started on immunization, according to the calendar.

Results: HBV vaccine coverage rates were 63% in the younger cohort and 50% in the older one. The results of univariate and multivariate regression analysis showed that starting HBV immunization was associated with being newborn (crude OR = 3.30; 95%CI 2.17-2.44), with living in a small city (crude OR = 6.81; 95%CI 6.12-7.58), and with being assigned to the second (crude OR = 1.77; 95%CI 1.65-1.90) or to the third 6-month period of the expected immunization period (crude OR = 2.58; 95%CI 2.42-2.76). The probability of completing HBV immunization was higher among children who had had the first dose "age-appropriately" or with "acceptable delay" and among those living in small cities. It was lower among children in the second or the third 6-month period. Size of urban area of residence was associated with both outcomes: the city of Rome showed the lowest probabilities of starting and completing HBV immunization, while the small cities showed the highest ones.

Conclusions: The performance of public health services was the most important determinant of recourse to public health services for vaccinations; it varied according to size of urban area; in towns organization difficulties contributed to the delay of starting vaccination, for at least a year. The expected immunization period was a good proxy indicator of services' performance. The timing of the first dose was the strongest predictor of completing vaccination also at the beginning of the campaign.