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Am J Public Health. 2004 June; 94(6): 978–984.
PMCID: PMC1448376

A Middle School Immunization Law Rapidly and Substantially Increases Immunization Coverage Among Adolescents

Abstract

Objectives. This study assessed the effectiveness of a middle school vaccination requirement for raising second-dose measles, mumps, and rubella vaccine and hepatitis B vaccine coverage among adolescents.

Methods. Random-digit-dialed telephone surveys were conducted before (1998) and after (1999) the implementation of a vaccination requirement for entry into the seventh grade in San Diego, Calif.

Results. Vaccination coverage was higher among children subject to the vaccination requirement (seventh-grade students; 60%) than among fifth- and sixth-grade students 1 year before the requirement (13%, P < .001), and 8th- through 12th-grade students not subject to the requirement (27%, P < .0001).

Conclusions. Middle school–entry vaccination requirements can rapidly and substantially raise vaccination coverage among students subject to the law.

The resurgence of more than 50 000 measles cases in the United States during the late 1980s1,2 and awareness that as many as 70% of the hepatitis B viral infections occur during adolescence and early adulthood3 led to recommendations that adolescents not already immune should receive hepatitis B (HB) vaccine and measles, mumps, rubella (MMR) vaccine, as well as tetanus and diphtheria (Td) toxoids and varicella vaccines.4 The recommendations call for a routine health care visit for children aged 11 through 12 years, during which they should be screened for and administered indicated vaccinations.

Although most states now require a second dose of MMR and HB vaccine for school entry,5 not all adolescents are up to date for MMR and HB vaccines because both vaccination recommendations and school entry requirements were phased in during the 1990s.1,2,6,7 Therefore, programs specifically targeting adolescents remain necessary.8 Middle school–entry vaccination requirements have been suggested as a way of ensuring vaccination of adolescents,4 and an increasing number of states have adopted middle school–entry vaccination requirements of 2 doses of MMR and HB vaccine.5 Although vaccination requirements have been shown to be effective in primary school,9 few data exist on their effectiveness in middle schools. A study from Florida suggests that middle school–entry vaccination requirements may be effective in ensuring vaccination of adolescents10; however, that report lacked data on the vaccination coverage of adolescents before enactment of the requirement.

BACKGROUND

In October 1997, the California legislature passed Assembly Bill 381 (AB381), requiring students entering the seventh grade to have received 3 doses of HB vaccine and 2 doses of MMR vaccine. The law made the new requirement effective July 1, 1999. Statewide, more than 470 000 children were subject to the requirement in the first year.

San Diego County is located in southern California bordering Mexico to the south and the Pacific Ocean to the west. The county has an ethnically diverse population of approximately 2.8 million and includes the city of San Diego, several suburban cities, rural agricultural areas, mountains, and deserts. An estimated 40 000 children entered seventh grade in 1999 and therefore were subject to AB381.

During 1997 through 2001, San Diego State University, Children’s Hospital and Health Center of San Diego, the San Diego County Health and Human Services Agency, the California Department of Health Services, and the Centers for Disease Control and Prevention collaborated to examine the implementation of AB381. This article assesses the effectiveness of AB381 in vaccinating seventh-grade students in San Diego County.

METHODS

Study Design

The design was a before-and-after observational study. The study’s sampling methodology consisted of 2 separate random-digit-dialed telephone surveys. A telephone survey was conducted to assess the vaccination status of children in fifth and sixth grades, 1 year before the institution of a seventh-grade vaccination requirement. The following year, after institution of the requirement, a second survey was conducted to assess the vaccination status of children in the seventh grade (i.e., children subject to the requirement). In addition, the vaccination status of children in the 8th through 12th grades was also assessed during the second survey.

First Survey, 1998

The first survey, conducted during April through June 1998 in conjunction with the San Diego County Health and Human Services Agency’s annual childhood vaccination coverage survey, targeted fifth- and sixth-grade students in San Diego County.5 To be eligible, a child had to be entering the fifth or sixth grade in the fall of 1998. Parents in participating households were asked to use the vaccination record in their possession to report dates of vaccinations received by their child. Health care providers were contacted if the parent did not have a parent-held record or if the child was not fully vaccinated. Health care providers were contacted only with parental consent.

Second Survey, 1999

This survey, which was conducted in 2 phases, targeted 7th- through 12th-grade students. The first phase, the identification of eligible subjects, was conducted during the spring of 1999 concurrent with the San Diego County Health and Human Services Agency’s annual childhood vaccination coverage survey. The second phase, interviewing eligible subjects, was conducted in the fall of 1999 so that the seventh-grade study participants would be subject to the vaccination entry requirement at the time of the interview (AB381 became effective in July 1999).

Households identified during the first phase were recontacted by telephone during October and November 1999 to conduct the interview. Parents were asked to use the parent-held vaccination record to report dates of vaccinations received. Experience from the first survey,8 conducted in 1998, found that contacting health care providers identified by parents yielded little additional data and did not justify the expense. Therefore, only the parent-held vaccination record was used to determine vaccination doses received.

Analysis

Data from both surveys were collected and entered into a database. The data were analyzed as a before-and-after trial with the vaccination coverage of fifth- and sixth-grade students representing the coverage of children before the intervention (i.e., the seventh-grade vaccination requirement) and that of seventh-grade students represented the coverage among children subject to the intervention. The vaccination coverage of 8th- through 12th-grade students, children who completed seventh grade when no seventh-grade vaccination requirement was in place, was considered that of a control or comparison population.

The outcome of interest was 3 doses of HB vaccine and 2 doses of MMR vaccine. Subjects with verified vaccination doses (by either parent-held vaccination record or provider records) were included in the analysis.

Strength of association was measured by standard univariate and stratified analysis. Mantel–Haenszel χ2 was used to assess the statistical significance of differences between subgroups of respondents. Multiple logistic regression was used to examine the independent contribution of characteristics associated with receiving required vaccinations among 7th- through 12th-grade students.

RESULTS

Characteristics of Survey Participants

Overall, 1610 (61.4%) of 2621 households with an eligible child participated in 1 of the 2 surveys. A total of 741 households contacted in April 1998 (first survey) had an eligible fifth- or sixth-grade student, and 489 (66.0%) of these households agreed to participate in the survey. Of the 1880 households contacted in October 1999 (second survey) with an eligible 7th- through 12th-grade student, 1121 (59.6%) participated in the survey; of these, 308 were seventh-grade students and 813 were 8th- through 12th-grade students. Of the 1610 who agreed to participate, 583 (36.2%) had a verified vaccination record and were eligible for the study. Seventh-grade students were more likely to have a verified vaccination record (166 [53.9%] of 308) than either fifth- and sixth-grade students (205 [41.9%] of 489) or 8th- through 12th-grade students (212 [26.1%] of 813) (P < .0001).

There were no significant differences in demographic characteristics among the 3 groups (Table 1 [triangle]). The racial and ethnic composition of the study participants was similar to the racial and ethnic composition of the overall San Diego County 10- to 19-year age group.11

TABLE 1
Characteristics of Study Participants: San Diego, Calif, 1998–1999

Vaccination Coverage

Overall, among the children with a vaccination record, coverage with 2 doses of MMR and 3 doses of HB vaccine (in full compliance with the seventh-grade entry requirement, AB381) was higher among seventh-grade students (61.7% [100 of 162]) than among fifth- and sixth-grade students (13.2% [27 of 205], P < .001) and 8th- through 12th-grade students (27.4% [58 of 212], P < .0001).

When vaccination coverage for the individual vaccines was examined, we found that 3-dose coverage with HB vaccine was higher among seventh-grade students (71.1% [118 of 166]) than among fifth- and sixth-grade students (16.1% [33 of 205], P < .0001) or 8th- through 12th-grade students (33.0% [70 of 212], P < .0001). The seventh-grade students were also more likely to have received at least 1 dose of HB vaccine (91.0%) compared with fifth- and sixth-grade students (42.0%, P < .001) and 8th- through 12th-grade students (62.7%, P < .001).

Two-dose measles vaccination coverage was also higher among the seventh-grade students (78.9% [131 of 166]) than among fifth- and sixth-grade students (70.2% [144 of 205] P = .057) or 8th- through 12th-grade students (60.1% [129 of 212] P < .0001).

We next looked at timing of receipt of vaccinations among the 3 groups of students. Before the law AB381 was passed in October 1997, 3-dose HB vaccination coverage was similar for the 3 groups (Figure 1 [triangle]). For the 6 months following passage of the law, there was little increase in the HB vaccine coverage among any of the groups surveyed. Because the fifth- and sixth-grade students were surveyed during April through June 1998, coverage data for the second half of 1998 and 1999 are not available for this group. For the period June 1998 through November 1999, the percentage vaccinated among the seventh-grade students showed a greater increase, from 21% to 71%, than that of the 8th- through 12th-grade students, who experienced an increase from 15% to 33% (P < .0001).

FIGURE 1
Hepatitis B vaccination coverage among students, by grade, 1996–1999.

Two-dose MMR coverage was higher than HB vaccine coverage in all 3 groups during December 1995 (Figure 2 [triangle]). The 2-dose MMR coverage during 1996 was higher among the fifth- and sixth-grade students (64%) and the seventh-grade students (63%) than among 8th- through 12th-grade students (45%) (P < .001 for both pairwise comparisons). From January 1996 through June 1998, coverage rose modestly for the 3 groups, reaching 70%, 67%, and 58% for the fifth- and sixth-grade students, seventh-grade students, and eighth-grade students, respectively. From June 1998 through November 1999, the coverage among seventh-grade students (i.e., the group subject to AB381) rose an additional 13% and reached 79%, whereas coverage among 8th- through 12th-grade students rose by 2% to reach 60%. The overall increase from January 1996 through November 1999 was 16% (63% to 79%) for seventh-grade students and 15% (45% to 60%) for the 8th- through 12th-grade students.

FIGURE 2
Two-dose measles, mumps, and rubella vaccination coverage among students, by grade, 1996–1999.

To examine coverage levels of individual grades, we disaggregated the coverage data of the fifth- and sixth-grade students as well as that of the 8th- through 12th-grade students. The coverage for both vaccines was similar among fifth-grade students (HB coverage = 19%, MMR coverage = 69%) and sixth-grade students (HB coverage = 16%, MMR coverage = 72%). Among the 8th- through 12th-grade students, we found that 3-dose HB coverage was higher among the eighth-grade students (56% [27 of 48]) than among the 9th- through 12th-grade students (26% [43 of 164], P < .001). Two-dose MMR coverage was also higher among eighth-grade students (71% [34 of 48]) than among 9th- through 12th-grade students (57.9% [95 of 164]), but the difference did not reach statistical significance (P = .11). There were no appreciable differences in vaccination coverage among the individual grades 9 through 12 for receipt of both HB vaccine and MMR vaccine (data not shown).

Factors Associated With Lacking Required Vaccinations Among 7th- Through 12th-grade students

Using multiple logistic regression, we compared students who received 3 doses of HB vaccine and 2 doses of MMR vaccine with those who did not. Students in seventh grade were more likely to receive 3 doses of HB vaccine and 2 doses of MMR vaccine than students in 8th through 12th grade; no other factors were found to be significantly associated with being vaccinated (Table 2 [triangle]).

TABLE 2
Multiple Logistic Regression of Factors Associated With 2 Doses of MMR Vaccine and 3 Doses of Hepatitis B Vaccine Among 7th- Through 12th-grade Students: San Diego, Calif, 1999

Tetanus and Diphtheria Toxoids and Varicella Vaccine

Although not required by AB381, participants were asked about receipt of Td toxoids and varicella vaccine. Td toxoids coverage was lower among fifth- and sixth-grade students (9.3% [19 of 205]) than among either seventh-grade students (42.8% [71 of 166], P < .001) or 8th- through 12th-grade students (41.5% [88 of 212], P < .001). There was no difference in coverage between the seventh-grade students and 8th- through 12th-grade students (P = .81). Varicella vaccine coverage estimates were limited to those with no prior history of varicella (i.e., chickenpox). Varicella vaccine coverage did not vary among the 3 groups; coverage was 23.1% [6 of 26] among fifth- and sixth-grade students, 32.3% [10 of 31] among seventh-grade students, and 23.5% [8 of 34] among 8th- through 12th-grade students (P > .40 for all pairwise comparisons).

DISCUSSION

This study demonstrates the effectiveness of a middle school–entry vaccination requirement in raising coverage of required vaccines among a high proportion of adolescents subject to the requirement over a short period of time. After its passage, AB381 substantially increased 3-dose HB and 2-dose MMR vaccination coverage among San Diego County adolescents subject to the requirement, whereas adolescents not subject to the requirement had much smaller increases in vaccination coverage over the same period of time. In addition, of the 40% of seventh-grade students not fully vaccinated, more than 90% had received at least 1 dose of HB vaccine. These findings suggest that adolescents subject to a middle school HB vaccine and MMR vaccine requirement are likely to be fully or partially protected from those diseases, in contrast to those children not subject to such a requirement. Although recommendations for vaccination of adolescents have been in place since 1996,4 annual increases in coverage among all the cohorts studied were modest until passage of the law dramatically increased coverage among the seventh-grade students; thus, although the recommendations did have some impact, the passage of AB381 had a much larger and more immediate impact on coverage. The results of this study support findings from a prior study in Florida.10 In addition, these findings are consistent with the effects of primary school–entry vaccination laws.9

Previous studies have shown that voluntary school-based vaccination programs can successfully vaccinate large numbers of adolescents.12–14 School-based vaccination programs offer advantages for tracking the vaccination status of students and have been shown to be cost-efficient when compared with provider-based vaccination.15 However, the success of such programs is largely dependent on financial support and motivated individuals working closely with students, parents, and school officials. Thus, such programs cannot reliably ensure vaccination of large numbers of adolescents in a state or county over time. Provider-based voluntary vaccination programs have also been shown to successfully vaccinate a large proportion of adolescents.16 However, such programs are also dependent on motivated individuals (i.e., health care providers).

In the absence of school-based vaccination programs, middle school–entry vaccination requirements are likely to result in more adolescents seeking care from their health care providers; this increase in visits provides an opportunity for delivery of other recommended preventive services.17 However, further study is necessary to determine whether providers will take advantage of these additional contacts with adolescents who are seeking vaccinations to comply with the school entry requirement and deliver not only the required vaccinations, but other recommended preventive services as well.

Our study also found that being in seventh grade was the only factor independently associated with receiving 2 doses of MMR vaccine and 3 doses of HB vaccine—no other factors predicted which adolescents were more likely to be vaccinated. This finding suggests that in the face of a vaccination requirement, social and economic factors may not be critical determinants of who does or who does not receive vaccinations. This is in contrast to studies among children and adults that found that, in the absence of mandates, significant disparities in vaccination coverage based on socioeconomic factors, race, and education may exist.18 It is also encouraging that statewide data from California showed that vaccination coverage for both HB and MMR vaccines continued to increase during the 1999–2000 school year.19

The low HB vaccine coverage before 1998 among all cohorts studied is consistent with the situation during that time when no programs were in place in California to ensure vaccination of adolescents, although the recommendations for vaccination of adolescents with HB vaccine were published in 199520 and reinforced in 1996.4 This suggests the inability of vaccination recommendations alone, in the absence of a program (i.e., the law), to substantially modify health care provider and public behaviors with respect to vaccination of adolescents. This is in contrast to the relatively rapid increase in infant HB vaccine coverage seen after the 1991 recommendations.7

It is important to remember that the purpose of school entry requirements is disease prevention. A small number of unimmunized persons can sustain measles transmission during an outbreak.1,2 A second dose of measles vaccine reduces the number of children experiencing vaccine failure, thus minimizing risk of transmission. Although the effect of the law on MMR vaccination coverage in our study was modest because of the relatively high measles vaccine coverage before the requirement, certainly many adolescents who would otherwise not have received a second dose of measles vaccine were vaccinated. The law should help in the control of measles in the event of a reintroduction or importation of measles.

The potential impact on prevention of hepatitis B is more significant. Among the estimated 40 000 students who entered seventh grade, if none had been vaccinated during their lifetime, an estimated 1680 (4.2% lifetime risk for persons older than 6 years) would have become infected with HBV, of which 100 (6% of infections) would have gone on to develop chronic liver disease/hepatocellular carcinoma.3 Given that 70% were fully vaccinated and more than 75% of those not fully vaccinated received 1 dose or more, the great majority have received complete or partial protection from hepatitis B. This middle school–entry vaccination requirement has proved to be an effective mechanism for ensuring that San Diego County’s adolescents will be protected from hepatitis B. In the absence of a law, most adolescents would not have received this vaccine. Currently, 30 states have implemented HB vaccine middle school vaccination requirements.5

This study was subject to limitations that need to be considered when interpreting the results. The participation and response rates were relatively low, and there were slightly differing methodologies for data collection between the first and second surveys, suggesting a risk for biased results. However, we found remarkably similar coverage rates for hepatitis B vaccine among all 3 groups during 1996—1998, and similar coverage rates for 2 doses of measles vaccine for the fifth- and sixth-grade students and the seventh-grade students during the same time period (Figures 1 [triangle] and 2 [triangle]). This would suggest that although the data collection methods varied for the 2 surveys, there was no appreciable bias in the results. In addition, the finding that seventh-grade survey coverage (60%) was similar to the coverage reported by the schools (67%)19 demonstrates the validity of telephone surveys for assessing adolescent vaccination coverage and, conversely, that school records, if available, may offer a low-cost method of accurately recording vaccinations received by adolescents. Further, the findings also suggest that there is little benefit in conducting a provider record check when assessing adolescent vaccination coverage—a costly and time-consuming component of coverage surveys. Until a gold standard method is established, and in the absence of reliable school records, vaccination coverage surveys without provider validation may be an appropriate and valid method for assessing adolescent vaccination coverage. For infant vaccination, a parent-held record and provider validation serve as a gold standard for coverage surveys.21

The findings from this study, achieving high vaccination coverage over a short time period, have policy implications for vaccines still under development that may one day be targeted for adolescents. Vaccines for prevention of sexually transmitted diseases including HIV infection, when available, should be administered during early adolescence, before risk-taking behaviors become common.22 Use of hepatitis B vaccine is an example of this paradigm. Risk factors for hepatitis B among adults and older adolescents include high-risk sexual activity and injection drug use. Hepatitis B vaccine has been commercially available in the United States since 1982 and is recommended routinely for adolescents aged 11 and 12 years since 1994.20 Our study found that hepatitis B vaccine coverage was low among all adolescents studied before implementation of the law, demonstrating that recommendations alone fail to significantly raise coverage in this age group. However, the middle school entry requirement was effective in rapidly raising vaccination coverage with this vaccine among those subject to the requirement, whereas coverage remained low among those not subject to the law.

Rapidly achieving high coverage among adolescents with new vaccines that prevent sexually transmitted diseases and HIV infection as they become available will continue to challenge clinicians and public health practitioners. There will be significant social and political pressures against the passage of laws to require vaccination of adolescents with such vaccines. However, without laws, it is likely that a scenario similar to that of hepatitis B vaccination–nearly 20 years since the availability of hepatitis B vaccine, there has been little penetration into key target populations—will play out with the next generation of sexually-transmitted-disease vaccines. Although our study demonstrates that middle school laws clearly have the ability to rapidly achieve high vaccination coverage among adolescents, further research is necessary to define the acceptability of using middle school entry requirements to achieve high vaccination coverage in this population.

Acknowledgments

This research was funded by the National Immunization Program of the Centers for Disease Control and Prevention under a cooperative agreement with the Association of Schools of Public Health.

The authors acknowledge the support of Sandra Ross, the director of immunization program at the San Diego County Health and Human Services Agency. Steve Klish and Nancy Fink, also from the San Diego County Health and Human Services Agency, were especially instrumental in completing the 1998 survey. Diana Simmes at the Center for Child Health Outcomes, Children’s Hospital and Health Center of San Diego, managed the data from the 1999 survey. We also acknowledge the thoughtful comments of Abigail Shefer at the National Immunization Program at the Centers for Disease Control and Prevention. Finally, our research assistants, Jennifer Rogers and Brandy George, as well as our administrative assistant, Mary Perl, are gratefully acknowledged for their important contributions to this project.

Human Participant Protection
This study was approved by the institutional review board of the San Diego State University, San Diego, Calif, and was exempted from review by the Centers for Disease Control and Prevention’s institutional review board.

Notes

Contributors
F. Averhoff designed the study and wrote the article. L. Linton contributed to the design, analyzed the data, and contributed to the writing of the article. K. Peddecord contributed to data analysis and the writing of article. C. Edwards contributed to data analysis and the preparation of tables and graphs. W. Wang contributed to the data analysis and to writing the article. D. Fishbein contributed to writing the article.

Peer Reviewed

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