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 [18
] 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
]. 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 [1
]. Another possible explanation for our results could be physicians having different knowledge about the vaccine and/or the recommendation [19
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 [20
]. Furthermore, in the 2006-2007 influenza season, only 31.8% of that age group had received at least 1 influenza vaccination [20
]. In Michigan, hepatitis A coverage has also risen much more rapidly than varicella vaccination. 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% [22
]. 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 [23
], 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” [15
]. 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 [24
]. 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 [24
One reason cited for low vaccination rates is often missed opportunity [25
]. 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 [25
]. 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 [25
]. 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 [25
As can be seen in , 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.
4.1. Strengths and Limitations
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 19–35 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 [16
]. 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.
The MCIR has some limitations that tend to bias its vaccination coverage measures downward. Although reporting of childhood vaccinations is legally required [26
] in Michigan, some vaccinations go unreported. Newly required vaccinations may also be subject to more incomplete reporting or more data entry error. MCIR is not always notified when children move out of Michigan. 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 [27
], we cannot entirely exclude differential reporting of vaccinations based on race, geographic region, type of health care provider, or insurance status. It is difficult to know how these biases might affect our results.
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-R2 (Nagelkerke R2 = 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.
4.2. Conclusions and Future Directions
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 [25
]. Data extracted from MCIR can also be used by public health officials to direct vaccine-specific education and outreach programs directly towards underserved populations [25
]. Studies have shown when vaccination education programs are paired with other strategies like reminder/recall, vaccination coverage increases for all subgroups of a population [25
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. Michigan will continue to monitor trends in hepatitis A vaccination coverage. Future studies could examine potential underlying causes for increased and decreased odds of vaccination receipt in specific groups.