This is the first validation study of parent-reported vaccinations compared with provider reports from medical records for adolescents. We found that parent-reported vaccination estimates using both immunization card and recall were more accurate than parent-reported estimates using recall only, and the validity of parent-reported vaccination estimates differed by vaccine type. Validity measures differed for routinely recommended childhood-administered vaccines (Hep B and MMR) and adolescent-administered and catch-up vaccines (VAR, Tdap, MCV4, and HPV4). Adolescents who participated in this study were born from 1990 through 1996 and turned 11 years of age from 2001 through 2007; adolescent vaccinations were recommended beginning in 2005.
Parents who reported childhood-administered vaccinations by immunization card/recall had moderate accuracy of reporting for Hep B compared with the provider report, but fair accuracy for MMR. However, parents who reported childhood-administered vaccinations by recall only had slight accuracy for both Hep B and MMR, with large net underreporting biases. Compared with childhood-administered vaccinations, parental report of adolescent-administered vaccinations by immunization card/recall was better, ranging from moderate to almost perfect accuracy. However, parental report of adolescent-administered vaccinations by recall only had fair accuracy for most vaccines, with larger net underreporting biases compared with the immunization card/recall group.
These findings are similar to those made by Suarez et al., who measured the validity of parents' reports of their children's vaccination status by recall. They found that the validity of a parent's recall depended upon the vaccine, and it decreased with increasing age of the child at vaccination and with an increasing number of vaccines that the parent had to remember.9
Similarly, the kappa values among both reporting groups in our study were lowest for vaccines given during childhood and highest for vaccines given during adolescence. The only exception is Hep B among the immunization card/recall group, which had moderate reporting accuracy, similar to that of the adolescent-administered vaccines. Using the immunization card may have removed some of the recall bias that made recalling older vaccinations harder compared with recalling more recent vaccinations. Incomplete immunization cards still may have contributed to inaccurate reporting from some parents among the immunization card/recall group.
HPV4 had the highest kappa values compared with the other adolescent-administered vaccines for both reporting groups. Gardasil®, the quadrivalent HPV vaccine (manufactured by Merck and Co., Inc., Whitehouse Station, New Jersey) has been the subject of a large marketing campaign by both Merck and professional medical associations.26,27
It has also had significant media coverage, which has increased public knowledge about HPV and its association with cervical cancer.28,29
The wide coverage of HPV4 may have made this vaccine easier to recall compared with other adolescent-administered vaccines (VAR, Tdap, and MCV4) that have not received equal media coverage. This may have contributed to the high reporting accuracy among parents. Similarly, because HPV is a sexually transmitted infection, discussions with physicians about HPV4 may have been more memorable to parents. For many parents, discussing their adolescent's sexual activity may be a sensitive topic, compared with discussing vaccines for non-sexually transmitted diseases. The negligible net bias for HPV vaccination from parental report can also be partly explained by the balancing of false-positive and false-negative reports. The false-negative rate ranged from 5.0% to 20.5%, depending on the reporting group and number of HPV doses.
Furthermore, as adolescent vaccination rates increase, the measures of association for parent-reported vaccination rates may change. With increasing knowledge of adolescent-administered vaccines and higher vaccine uptake, the validity of parental report may improve. On the other hand, as these vaccinations become more routine, the validity of parental report may also decline as parents pay less attention to the administration of these specific vaccines. Because these measures of association may change over time, the validity of parental report should be reevaluated periodically as vaccination uptake and knowledge about the vaccines improve.
In our study, reporting an adolescent's vaccination status from parent-held immunization card/recall gave more accurate vaccination estimates compared with reporting by parental recall only. Additionally, adolescents of parents who reported by immunization card/recall were more likely to be vaccinated with each vaccine compared with adolescents from the recall-only group. Having an immunization card available has been associated with higher vaccination coverage among young children.9,30
Yet, only 21.3% of respondents to our household survey had an -immunization card available. This percentage is less than the 32.2% (unweighted) of parents who reported by immunization card/recall in the 2008 NIS for children 19–35 months of age.31
The availability of an immunization card among parents participating in validity studies of young children has ranged from 21% to 72% and differs by study setting.7,9,10,32,33
Few parents carry immunization cards with them when accessing acute or preventive health care for their young children.7,10,33
As children age into adolescence, they have fewer preventive health-care visits, and immunizations become less frequent.34
Also, as participation in immunization information systems (IISs) increases, parents may be less motivated to carry immunization cards and keep them current. Consequently, parents of adolescents may then be less likely to have an easily accessible immunization card in the home or to bring it to a health visit. However, it has been suggested that immunization cards improve communication between parents and providers and prompt discussions about vaccinations.30
The recommendation to use each medical visit as an opportunity to evaluate one's vaccination status can be hindered when accurate vaccination information is not available. As seen among younger children, practitioners who receive inaccurate vaccination information may miss opportunities to vaccinate vulnerable adolescents or may even vaccinate when unnecessary.33
To improve vaccination histories provided by parents in the absence of medical records, parents and adolescents should be encouraged to bring the adolescent's immunization card to all medical encounters. Likewise, vaccination providers should reissue new immunization cards if they are missing. Bringing the immunization card to all medical visits should improve the completeness of the card, allowing the same immunization card to be updated with each vaccination. Similarly, vaccination-provider participation in the state's IIS is a necessary component for developing comprehensive immunization registries that could be accessed when evaluating an adolescent's vaccinations. IISs allow for accurate vaccination surveillance at state and local levels, aid the identification of subgroups of unvaccinated individuals, and assist in the information exchange between different vaccination providers and facilities, which leads to improved vaccination coverage.35,36
This analysis had a few limitations. It is unclear if parents who did not respond with immunization cards did not actually possess an immunization card. Misclassification bias may have occurred if parents who had an immunization card available decided to respond by recall. A higher proportion of parents from the recall-only group responded “don't know” about their adolescent's vaccination status compared with parents from the immunization card/recall group. Because “don't know” responses were considered “no” responses, misclassification bias may have contributed to higher false-positive and false-negative rates in both reporting groups.
Another limitation was the possibility of incomplete provider-reported data. Administered vaccines that are missing from provider records may contribute to higher false-positive rates. Although weighting adjustments were made to account for nonresponse and households without landline telephones, some response bias may remain. Finally, our analysis was limited to adolescents with records from all named vaccination providers among those with adequate provider data, comprising 53% of those with completed household surveys. Potential bias resulting from limiting our analysis to this group may have led to higher reported vaccination estimates and lower false-positive rates compared with the general population, which may have more record scattering among providers.