SUPPLEMENT ARTICLE
Progress toward Implementation of a Second-Dose
Measles Immunization Requirement for All
Schoolchildren in the United States
Maureen S. Kolasa, Sonia Klemperer-Johnson, and Mark J. Papania
National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia
In 1998, the Advisory Committee on Immunization Practices and the American Academy of Pediatrics recommended that states ensure that all children in grades kindergarten through 12 receive 2 doses of measlesmumps-rubella (MMR) vaccine by 2001. In 2000, the National Immunization Program surveyed states, the
District of Columbia, and United States territories, commonwealths, and protectorates to assess progress
toward this goal. Almost all respondents (53 [98%] of 54) reported a second-dose requirement for entry to
elementary school, middle school, or both. By fall of 2001, most (82%) school-aged children in the United
States were in grades requiring a second dose of measles vaccine. For 29 responding programs, the requirement
did not yet affect all grades. By 2009, 52 of 54 responding programs will require a second dose for all grades.
Although not all states have achieved coverage of all schoolchildren with 2 doses of MMR vaccine, most states
are well on their way toward this goal.
Requiring immunizations at school entry has been a
cornerstone of the US immunization program since the
1970s [1]. By the early 1980s, state requirements for a
single dose of measles vaccine before school entry were
instrumental in reducing the number of reported measles cases to record low levels [1]. However, outbreaks
of measles continued to occur, mainly among unvaccinated preschool-aged children and vaccinated adolescents [2]. Primary vaccine failure (the lack of an
effective immune response) contributed to the high
proportion of cases among vaccinated children [3–5].
In 1989, to increase levels of immunity to measles
in schoolchildren, the Advisory Committee on Immunization Practice (ACIP), the American Academy of
Pediatrics (AAP), and the American Academy of Family
Physicians (AAFP) recommended that schoolchildren
receive a second dose of measles vaccine [6–8]. However, the ACIP, AAP, and AAFP did not agree on the
timing of the second dose. The ACIP and AAFP rec-
Reprints or correspondence: Dr. Maureen S. Kolasa, Centers for Disease Control
and Prevention, 1600 Clifton Road, Mailstop E-61, Atlanta, GA 30333 (mxk2@
cdc.gov).
The Journal of Infectious Diseases 2004; 189(Suppl 1):S98–103
This article is in the public domain, and no copyright is claimed.
0022-1899/2004/18909S1-0016
S98 • JID 2004:189 (Suppl 1) • Kolasa et al.
ommended that children be vaccinated before entering
elementary school, whereas the AAP recommended that
adolescents receive a second dose before entering middle school [6]. State immunization programs began
adopting second-dose school entry requirements, following either the recommendations from ACIP/AAFP
or those of AAP. A few states adopted both recommendations and required 2 measles vaccinations of children entering both elementary and middle school [9].
Subsequent measles outbreaks demonstrated the effectiveness of a second dose at inducing an immune
response in people who remained seronegative after
a first dose and in preventing measles [10]. During a
1994 measles outbreak in Colorado, measles was contracted by 7 (44%) of 16 unvaccinated children and
10 (3%) of 320 children with only a single dose of
measles vaccine, whereas none of the 289 children who
had received 2 doses of measles vaccine developed
disease [11]. In another outbreak among school-aged
children in Utah, a single dose of measles was 97%
efficacious, and 2 doses were 100% efficacious in preventing disease [12].
Because outbreaks continued to occur among schoolaged children not covered by a second dose, additional
efforts were made to immunize all school-aged children
with a second dose of measles vaccine [12]. In 1998, the
ACIP, AAP, and AAFP synchronized their recommendations
for a second dose before elementary school entry. In addition,
the ACIP and AAP recommended that states require that all
school-aged children receive a second dose of measles vaccine
by 2001 [13, 14].
We conducted a survey to assess states’ progress toward the
goal of coverage of all school-aged children with 2 doses of
measles vaccine by 2001. Survey objectives were to describe
when states implemented a second-dose requirement, how
states assess second-dose coverage, and by what year all schoolaged children will be covered by the second-dose requirement.
We also reviewed other data from the Health Employment Data
Information Set (HEDIS) and the National Health Interview
Survey (NHIS) for information regarding receipt of 2 doses of
measles vaccine among school-aged children.
METHODS
A survey was sent via e-mail to the immunization program
managers of every state, the District of Columbia, and the 8
territories, commonwealths, and protectorates of the United
States. We collected data on the following: whether and when
laws were enacted that require that children receive 2 doses of
measles vaccine; type of measles vaccine required for the second
dose; what grades are required to receive 2 doses in 2001; by
what year all grades will be covered by the laws; whether the
state or territory has any plans for accelerating coverage by
grade; how second-dose measles vaccination coverage is assessed; and results from any such assessments.
US census data were used to determine the size of grades
for all states, the District of Columbia, Puerto Rico, and the
Northern Mariana Islands [15]. Estimates of populations by
single-year age were available for 1989–1999 for all states and
the District of Columbia. Estimates of population by 5-year
age groups were available for 1990–2001 for Puerto Rico and
the Northern Mariana Islands. We assumed that each age would
correspond to a single grade (e.g., 5-year-olds were considered
to be kindergartners, 6-year-olds were considered to be first
graders). We determined the grade populations in Puerto Rico
and the Northern Mariana Islands by dividing each 5-year age
group into single-year age groups and calculated a 5-year moving average to smooth the data. School enrollment numbers
are submitted by the Federated States of Micronesia to the
Centers for Disease Control and Prevention (CDC).
We used Microsoft Access and Excel for data entry and
analysis. For states that assess second-dose measles vaccination
coverage, we used the census estimates to calculate populationbased coverage levels. To estimate population-based coverage
levels for future years, we projected current data to future years.
To estimate the impact of second-dose measles vaccine requirement for schoolchildren, we plotted the numbers of con-
firmed measles cases among persons 5–19 years of age reported
by states to the CDC. We excluded imported cases occurring
in persons who are not residents of the United States.
RESULTS
The survey response rate was 92% (54/59). All 50 states, the
District of Columbia, Puerto Rico, the Northern Mariana
Islands, and the Federated States of Micronesia returned the
survey. The 5 nonresponders were all island territories. For
the remainder of this paper, all responders will be referred to
as “states.”
By fall 2001, almost all (53 [98%] of 54) states require a
second dose of measles vaccine at school entry, either at elementary school entry, middle school entry, or both. Idaho is
the only state that has no requirement and no future plans to
require a second dose of measles vaccine for school entry. The
majority of states (36 [67%] of 54) have both elementary and
middle school entry requirements. A number of these states
introduced middle school entry requirements in the early 1990s
and implemented a kindergarten requirement only after the
1998 recommendations.
About one-quarter of states (14 [26%] of 54) rely solely on
elementary school entry requirements. Three states (6%) have
only middle school entry requirements, and all of these states
plan to implement second-dose entry requirements for kindergarten in the near future. Most states implemented school
entry requirements gradually, requiring 1 or 2 grades be vaccinated per year, but 16 states (30%) required all or many grades
be vaccinated in a single year.
Although measles vaccine is usually given in combination
with mumps and rubella vaccines (MMR) for the first dose,
states vary in what vaccines are required for the second dose.
A majority of states (32 [59%] of 54) simply require that children receive a measles-containing vaccine. About one-third of
states (19 [35%] of 54) require that children receive the MMR
vaccine, and 2 states require the measles and rubella vaccine.
States also vary in their approach to new entrants into the
school system. When a child moves to a different state, the
child may not be in compliance with the new state’s immunization requirements. Most states (39 [72%] of 54) require
that new entrants into the school system be vaccinated with 2
doses of measles vaccine. A majority of these (22 [56%] of 39)
require a second dose of measles vaccine for entrants into all
grades, whereas 17 states (44%) require a second dose of measles vaccine only of new entrants into grades already covered
by their second-dose requirement.
All states that require a second dose of measles vaccine assess
vaccination coverage through ⭓1 of the following methods:
self-report by all schools; self-report by all elementary, all middle, or all high schools, but not all 3 types of schools; validation
Second-Dose Measles Immunization Requirement • JID 2004:189 (Suppl 1) • S99
Table 1.
State methods for assessing immunization coverage in school students.
No. (%) of states by reporting method
Validation method
Validation audits, all schools
Validation audits, sample of schools
No validation audits
Total
All schools
self-report
1 (2)
18 (33)
Some schools
self-report
0
17 (32)
No schools
self-report
Total
6 (11)
7 (13)
3 (6)
38 (70)
7 (13)
1 (2)
1 (2)
9 (17)
26 (48)
18 (33)
10 (19)
54 (100)
audits on a sample of schools; or validation audits on all schools
(table 1). Most states (38 [70%] of 54) conduct validation audits
on a sample of schools, whereas 7 states (13%) conduct validation audits in all schools and 9 (17%) do not conduct validation audits. Some states assess only whether children are
compliant with all immunization requirements and do not assess for specific vaccines, such as the measles vaccine.
Measles vaccine coverage is assessed among elementary
school students in 38 states and among middle school students
in 25 states. The median immunization coverage level for the
second dose of measles vaccine was 97% (range, 57%–99%)
for students entering elementary schools and 98% (range, 62%–
99%) for students entering middle schools.
According to the survey results, by the fall of 2001, most
(82%) school-aged children in the United States were in grades
for which a second dose of measles vaccine was required. As
the percent of children covered by a second-dose requirement
has increased, the reported numbers of measles cases among
school-aged children has decreased, from almost 10,000 per
year in 1989–1990 to !50 per year for 1997–2001 (figure 1).
Twenty-five states met the goal of covering all cohorts in
grades kindergarten through 12th grade with a 2-dose measles
vaccine requirement by 2001 (figures 2 and 3). Either by using
projected data provided by states or by projecting current data
to future years, we estimate that 52 of 54 states will have required a second dose for all grades by 2009 (figure 2). One of
the remaining 2 states does not require a second dose for any
grades, and the other state requires a second dose for middle
school entry only.
On the basis of data obtained by this survey, we calculated
the impact of the recommendation for a second dose of measles
vaccine on susceptibility to measles among children aged 5–17
years in 2001. To do this calculation, we made the following
assumptions: the seroconversion rate after the first dose of
measles vaccine is 95%, and of those who do not seroconvert
after the first dose, seroconversion after the second dose is 95%
[11, 13, 16, 17]; coverage in the United States for 1 dose of
measles vaccine at school age is 96% [18], and on the basis of
the data herein, 82% of school-aged children are covered by a
second-dose measles requirement. Using these assumptions, we
estimate that without a second-dose recommendation, 4.5 million school-aged children would have been susceptible to measles in 2001. With the second-dose recommendation and current coverage levels, only ∼650,000 school-aged children were
susceptible to measles in 2001.
Figure 1. Comparison of school-aged children (ages 5–19 years) covered by a 2-dose measles vaccine requirement and measles cases in schoolaged children, 1989–2001.
S100 • JID 2004:189 (Suppl 1) • Kolasa et al.
Figure 2.
Number of states with 2-dose measles vaccine requirement for all children in kindergarten through grade 12 (K-12), 1992–2009
DISCUSSION
In accordance with the 1998 policy recommendations, by 2001
almost all states had implemented second-dose measles vaccine
requirements for school entry. Although only 25 states achieved
the 2001 goal of complete coverage of all schoolchildren with
a requirement for 2 doses of a measles vaccine, most states are
well on their way toward this goal, and measles cases in schoolaged children are at an all-time low [19].
Various grades are covered by states’ second-dose measles vaccination laws, with some states requiring the second dose at entry
to elementary school, others at entry to middle school, and still
others at both elementary and middle school entry. This variation
likely results from different second-dose recommendations given
by ACIP, AAP, and AAFP in 1989. Synchronization of second-
Figure 3.
dose measles vaccination recommendations in 1998 has helped
to decrease this variation among states.
Methods used to assess immunization coverage levels and
approaches to new entrants into the school system differ greatly
between states; thus, comparing coverage data among states is
problematic. In addition, not all states assess receipt of 2 doses
of measles vaccine among new entrants (i.e., transferring students) into a school system. This creates the opportunity for
failure to identify underimmunized children. For example, a
child in elementary school with only 1 dose of measles vaccine
moving from a state with a middle school entry requirement
to a state with an elementary school entry requirement might
not be identified as needing a second dose.
It is important to distinguish vaccine coverage from a vaccine
Number of grades covered by school requirements for second-dose measles vaccination in 2001
Second-Dose Measles Immunization Requirement • JID 2004:189 (Suppl 1) • S101
requirement. State assessments indicate that a median of 97%–
98% of children subject to a 2-dose requirement have received
2 doses. On the other hand, many children may be vaccinated
without being subject to a requirement. According to data collected in 1997 by HEDIS on children enrolled in managed care
organizations, the mean plan coverage of 13-year-olds for 2
doses of MMR was 61% [20]. In 1997, data from the NHIS
indicated that 89% of 13- to 15-year-olds had received a second
dose of measles vaccine [21]. In comparison, the results of our
survey showed that !50% of middle school–aged children in
the United States had actually been required to receive a second
dose of measles vaccine by 1997. This suggests that actual 2dose measles vaccine coverage may be substantially higher than
coverage solely calculated with a state requirement for 2 doses,
especially among adolescents.
The high coverage results for 2 doses of measles vaccine as
reported by HEDIS and NHIS are further verified by data 6
states submitted to the CDC on assessments of second-dose
measles vaccination coverage among grades not covered by the
school entry requirements. These states reported a median coverage level for 2 doses of measles vaccine of 60% among children not required to receive the second dose and a median
coverage level of 197% among children covered by a seconddose requirement. Many physicians and parents appear to have
followed the recommendations of ACIP, AAP, and AAFP and
vaccinated children with 2 doses of measles vaccine, even if this
was not yet required by the state. The fact that second-dose
coverage among children not required to receive the second
dose is lower than coverage among children who are required
to have the second dose suggests that school entry requirements
are at least partially responsible for increasing the level of second-dose coverage.
Study limitations include our reliance on self-reports from
states regarding their second-dose laws: we did not review state
legislation ourselves. We also relied on state reports of seconddose coverage, which are limited because states use various
methods to assess second-dose coverage, and 17% of states (9/
54) do not conduct validation audits on their assessment results.
Because most surveyed states submitted data only for grades
covered by second-dose immunization requirements, we could
not ascertain coverage levels in grades not covered by the requirements. We did not use school enrollment figures, which
would have given us a better indication of the actual numbers
of children affected by these laws.
In summary, although not all states have yet achieved coverage of all schoolchildren with 2 doses of measles vaccine,
most states are well on their way toward this goal. Almost all
states have implemented second-dose measles vaccine laws
for school entry, and by 2009, all but 2 states will require
schoolchildren in every grade to have 2 doses of measles vaccine. Because of the variation among states in requiring the
S102 • JID 2004:189 (Suppl 1) • Kolasa et al.
second dose at elementary school and middle school entry,
we recommend that all new entrants into the school system
be assessed for 2 doses of measles vaccine. High second-dose
measles vaccine coverage in schoolchildren has resulted in an
extremely low incidence of measles in schoolchildren and is
one of the cornerstones of the measles elimination strategy
in the United States.
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