hepatitis a was one of the most frequently reported vaccine - preventable diseases in the united states in the 1990s . typically , infection rates in the u.s . were higher in children under six years of age , adults over 50 years of age , american indians , alaska natives , hispanics , and lower socioeconomic groups     [ 17 ] . since hepatitis a vaccination introduction , infection rates in the u.s . have dropped drastically , especially in groups with the highest disease incidence historically     [ 35 , 8 ] . the advisory committee for immunization practices ( acip ) made initial recommendations in 1996 to vaccinate all high - risk groups ( i.e. , travelers and iv drug users ) , and the target populations have been expanded several times     [ 911 ] . the 1999 recommendations included routine vaccination of children   2 years of age living in areas with hepatitis a incidence consistently   2 times the national average of 10 cases per 100  000 ; this included 11 states located in western and southwestern regions of the united states .   in may , 2006 , the acip recommended routine vaccination of all 1223 month old children in the united states with 2 doses at least 6 months apart .       in 2003 , data collected from the national immunization survey ( nis ) showed 50.9% coverage ( 1 dose ) among 24 to 35 month old children in the 11 states where recommendations for routine vaccination had been made versus only 1.4% of children in the same age group in the rest of the country . some studies have found significant postrecommendation increases in vaccination receipt and decreases in hepatitis a incidence among american indians and alaska natives [ 2 , 5 ] . other groups that have had significantly increased odds of receiving the hepatitis a vaccination include women , people with public ( as opposed to private ) health providers , children living in urban areas , and children born to mothers with lower levels of education     [ 2 , 7 , 12 , 13 ] . michigan care improvement registry ( mcir ) , michigan 's immunization information system ( iis ) has collected data on hepatitis a vaccination in one - year - olds since the recommendation has been implemented in michigan . mcir is one of the leading iiss in participating number of children younger than 6 years , and in participating public and private vaccination provider sites [ 14 , 15 ] . the primary goal of this study was to determine factors associated with hepatitis a vaccination in one - year - olds in michigan after the 2006 routine recommendations were implemented . it was hypothesized that being hispanic , being american indian , being of lower socioeconomic status ( by medicaid and wic status ) , and living in nonrural areas would all increase the odds of vaccination receipt in michigan , similar to findings in other states . a secondary objective was to assess overall hepatitis a vaccination coverage levels among one - year - olds in michigan . the study population contained 134  226 one - year - olds in mcir who had their first birthday on or between may 1 , 2006 and april 31 , 2007 . these children were the first eligible cohort of one - year - olds for hepatitis a vaccination following acip 's may 2006 recommendations for universal vaccination . this study uses data from the michigan care improvement registry ( mcir ) . at the end of 2007 , more than 95% of children 1935 months of age had at least two recorded vaccinations in mcir , and approximately 91% of the 2255 michigan childhood vaccination providers submitted data to mcir from july to december 2007 . coverage estimates from the mcir generally fall within the 95% confidence limits of michigan 's vaccination coverage measures in 1935 month olds according to the national immunization survey ( k. enger , unpublished observations ) . the primary outcome variable was receipt of at least one dose of hepatitis a vaccination by the time the child turned two . the explanatory variables tested were gender , race / ethnicity , mother 's age , number of months the vaccination recommendation was in effect by the child 's first birthday , provider type ( public versus private ) , medicaid status , wic status , rurality , and geographic region within the state , defined by mcir region ( figure 1 ) . medicaid and wic status were defined as anyone enrolled in medicaid and/or wic at the time the child turned one ( when they were first eligible for vaccination receipt ) . the rurality variable was created using categorization f of the university of washington 's rural - urban commuting area codes ( rucas ) . this classification system uses zip code and census tract commuting information to create categorizations of urban and rural areas . categorization f created a rural category where only those areas that have little to no commuting of residents to larger areas for recreation or work are classified as rural . descriptive statistics were used to describe the study population and assess vaccination coverage following the recommendations . differences in child characteristics by vaccination status were assessed using chi - square tests for categorical variables and anovas for continuous variables . unadjusted logistic regression models were also used as a means of calculating odds ratios and 95% confidence intervals to assess the relationships between covariates and hepatitis a vaccination receipt . a main effects multivariable logistic regression model was used to determine adjusted measures of association , adjusted for all covariates with p   < .05 at the bivariate level . all possible two - way interactions of race / ethnicity with medicaid / wic status and two - way interactions between race / ethnicity and provider type were assessed in other logistic regression models . the main effects model was compared with the full model ( containing the interaction terms ) using the likelihood ratio test to determine if an interaction effect was present . this study was approved by the institutional review boards of the michigan department of community health and the university of michigan . there were 134  226 one - year - olds included in these analyses ; 15  540 ( 11.6% ) were excluded from multivariable analyses due to missing values for   1 variables .   of all mcir - enrolled one - year - olds , 55.8% ( n = 74885 ) received at least one dose of the vaccine by the time of their second birthday . specific coverage rates varied by race / ethnicity , medicaid and wic status , mother 's age , time the recommendation had been in effect by the child 's first birthday , and geographic location ( table 1 ) .   by the time of a child 's second birthday , only 0.06% ( n = 81 ) received a full two - dose series . the multivariable logistic regression model with interaction terms for race / ethnicity and medicaid / wic status was significantly different from the main effects model , based on the log - likelihood test with p < .05 , and will therefore be the only multivariable model reported . in the multivariable model ( table 2 ) , the odds of vaccination differed significantly by race / ethnicity , provider type , medicaid / wic enrollment , residence in a rural zip code , and by region within michigan . compared to one - year - olds who were white , each of the minority race / ethnic groups had statistically higher odds of receiving a vaccination : asian and asian pacific islander ( odds ratio [ or ] = 1.75 ;  95% confidence interval [ ci ] : 1.58 ,  1.95 ) , black ( or = 1.09 ;  95% ci : 1.01 ,  1.29 ) , and hispanic ( or = 1.16 ;  95% ci : 1.07 ,  1.26 ) ( table 2 ) . children visiting a public provider were more likely to receive the vaccination than children seeing a private provider ( or = 1.19 ;  95% ci : 1.13 ,  1.25 ) ( table 2 ) . children on medicaid and wic together had increased odds ( or = 1.38 ;  95% ci : 1.31 ,  1.44 ) of vaccination receipt when compared to children receiving neither service ( table 2 ) . children living in rural areas had decreased odds ( or = 0.88 ;  95% ci : 0.80 ,  0.96 ) of receiving a vaccination , when compared to children living in nonrural areas ( table 2 ) . northern , less - populated areas of michigan ( regions 3 , 5 , and 6 ) were less likely to be vaccinated than southern , more densely populated areas ( regions 1 , 2 , and 4 ) ( table 2 and figure 1 ) . significant interaction was also present between hispanic or black race / ethnicity and medicaid / wic enrollment ( table 2 ) .   among children with medicaid , hispanic children had 1.83  ( 95% ci : 1.40 ,  2.41 ) times the odds of being vaccinated than white children .   among children with wic , hispanic children ( or = 1.35 ;  95% ci : 1.10 ,  1.67 ) and black children ( or = 1.17 ; 95% ci : 1.01 ,  1.34 ) had increased odds of vaccination receipt when compared to white children ( table 2 ) . compared to white children on both medicaid and wic , black children ( or = 1.17 ;  95% ci : 1.05 ,  1.29 ) and hispanic children ( or = 1.32 ;  95% ci : 1.12 ,  1.56 ) again had increased odds of receiving the vaccination ( table 2 ) . hepatitis a vaccination was statistically associated with race / ethnicity , provider type , region , mother 's age , time the recommendation had been in effect by the child 's first birthday , and rurality in michigan . hispanic and black children receiving medicaid , wic , or both have increased odds of receiving the vaccination . these results are in contrast to the general trend of lower vaccination coverage among minority groups   and indicate that something may be differentiating promotion and administration of the hepatitis a vaccine from other vaccines . these results suggest that wic and medicaid may be promoting hepatitis a vaccination more effectively for hispanic and black children than for white children . our results are consistent with the previous findings showing that hispanic children , children with public insurance ( and probably lower socioeconomic status ) , and children who live in nonrural areas have increased odds of hepatitis a vaccination receipt     [ 2 , 7 , 12 , 13 ] .   one possible explanation for this could be that some groups of children are being targeted more because they have historically had a high risk for the disease .    another possible explanation for our results could be physicians having different knowledge about the vaccine and/or the recommendation . the high coverage rate ( 55.79% ) with 1 or more doses of hepatitis a vaccination in the first cohort of one - year - olds eligible for routine vaccination is remarkable . for example , the cdc recommended that all 6 to 23 month year olds in the u.s . should be vaccinated for influenza for the 2002 - 2003 season , but only 7.4% of that age group received at least 1 influenza vaccination . furthermore , in the 2006 - 2007 influenza season , only 31.8% of that age group had received at least 1 influenza vaccination [ 20 , 21 ] .   in michigan , although varicella and hepatitis a vaccinations are both recommended at the first birthday , it took three years following varicella recommendations for coverage to reach 39.6% .    while less than 1% of these children received a full two - dose series by the time of their second birthday , we believe this is probably explained in large part by the recommendation stating vaccinations to be at least 6 months apart , so many children probably go longer than the 6 month minimum before receiving the second dose . it is important to note , however , that the 6-month interval between first and second doses is longer than other recommended vaccination intervals , which may lead to failure of followup of the second dose . many children may be visiting a doctor according to the american academy of pediatrics ' well child visit schedule , and if a child visits a doctor just shortly before they are eligible to receive the second vaccination , they may go many months before seeing a doctor again , and the opportunity to vaccinate with the second dose may be missed .   the rapid uptake of hepatitis a vaccination may be due to the existence of the vaccine well before recommendations were implemented , improved vaccination promotion ( including assessment of hepatitis a in mcir ) , the degree of use prior to generalized recommendations for all children , perceived differences in severity between varicella and hepatitis disease or some combination of these . another reason for the rapid uptake could be mcir itself .   as one article put it concisely , iiss are among the most mature public health information systems that bridge the public health / clinical care divide  .   within the last 20 years , vaccination schedules for children have gone from providing protection from seven infectious diseases , and a total of 11 doses in the 1980s , to providing protection from 16 infectious diseases and a total of 30 to 40 doses in 2007 . iiss allow all providers to have access to the most up to date vaccination information for every child to whom they are providing care , which helps keep track of such a complex vaccination schedule . if a child is in to see a physician for a reason other than routine vaccinations , the physician may not take that opportunity to vaccinate the child . mcir and other iiss play an important role in reducing missed opportunity because they can be used in to produce vaccination reminders when it is time for a child to come in , and recall notices can be produced when a child is late for his / her vaccination . such reminder and recall notices can also be generated to send directly to homes , so parents are aware that a child is due for a vaccination . studies looking at offices where reminders and recalls are regularly used have an overall increase in vaccination coverage for children from all different population subgroups .     as can be seen in table 1 , region 6 had quite a remarkably lower vaccination rate that region 4 . we believe this may be partially due to region 6 being more rural and being  whiter . however , these things were adjusted for in multivariable analyses , and the difference in vaccination receipt still persisted . lower vaccination receipt in region 6 may also be explained in part by differences in the culture and/or beliefs between providers and residents in different regions . for example , there may be difference in beliefs about the need for or effectiveness of vaccines between regions , but mcir does not collect any information on this . we also do not have any data on vaccine promotion by region , and this may be a factor influencing differences between regions . a strong point of this study is the high quality of the data from mcir . at the end of 2007 , more than 95% of children 1935 months of age had at least two recorded vaccinations in mcir , and approximately 91% of the 2255 michigan childhood vaccination providers submitted data to mcir from july to december 2007 .   with such high participation rates , and a large sample size , we are confident that michigan 's population of one - year - olds was well represented in this data set . although reporting of childhood vaccinations is legally required   in michigan , some vaccinations go unreported . newly required vaccinations may also be subject to more incomplete reporting or more data entry error . therefore , if an unvaccinated child leaves the state and is subsequently vaccinated , that child could still be considered an unvaccinated michigan resident in mcir , further biasing vaccination coverage downward . actual vaccination coverage levels in michigan are probably slightly higher than estimates from mcir .    bias in vaccination reporting to mcir is a concern because of inherent differences in the types of people who visit doctors , and in the type of doctors who consistently update mcir information . although participation in mcir is good overall , local health departments tend to participate more fully than private health care providers , and some race / ethnic groups may be more likely to visit public providers . for example , a larger percentage of american indian , hispanic , and black one - year - olds received their vaccinations from public providers than white one - year - olds . in addition , southeast michigan has had lower mcir participation than the rest of the state ; since 83% of the residents of the city of detroit ( which is in southeastern michigan ) are black , we can not entirely exclude differential reporting of vaccinations based on race , geographic region , type of health care provider , or insurance status . the multivariable analyses in this study were limited to one - year - olds who were born in michigan because some of the explanatory variables were provided to mcir via michigan 's electronic birth certificate . if a child was born outside michigan , mcir would lack electronic birth certificate information , which would lead to missing values for some of the explanatory variables , causing that record to be excluded from the model .     although this analysis found significant associations between hepatitis a vaccination and several factors , the final model has low pseudo - r ( nagelkerke r = 0.01 ) . this indicates that other variables that were not included in our analysis may be needed in order to fully explain the variation in hepatitis a vaccination coverage . this indicates that further research may be necessary to determine more important factors associated with vaccination . likely candidates include socioeconomic status and education , which we were not able to measure directly . these data provide a baseline for hepatitis a vaccination coverage in michigan one - year - olds following the recommendation of hepatitis a vaccination for children nationwide . as shown in this study , iiss are a valuable tool , as the data gathered within them can be used to see if there are specific subgroups of a population not getting a vaccination or getting a vaccination at higher rates than the rest of the population . data extracted from mcir can also be used by public health officials to direct vaccine - specific education and outreach programs directly towards underserved populations . studies have shown when vaccination education programs are paired with other strategies like reminder / recall , vaccination coverage increases for all subgroups of a population . further outreach efforts may be needed to increase hepatitis a vaccination levels among those not receiving the vaccination , and these efforts should be specialized to this vaccine as its trends appear different from other vaccines . future studies could examine potential underlying causes for increased and decreased odds of vaccination receipt in specific groups .
the objectives of this study were to determine factors associated with hepatitis a vaccination and to assess overall hepatitis a vaccination coverage levels among one - year - olds in michigan . 
 the study population was the first hepatitis a vaccination - eligible birth cohort ( n = 134  226 ) enrolled in the michigan care improvement registry ( mcir ) after 2006 recommendations were made to routinely vaccinate all one - year - olds . 
 all children whose first birthday occurred on or between may 1 , 2006 and april 31 , 2007 were included in the study population . 
 racial / ethnic minorities had increased odds of receiving the hepatitis a vaccination in michigan , and medicaid and wic status modified this relationship . 
 fully understanding these relationships will be useful in targeting vaccination outreach and education programs .