Open Journal of Statistics, 2012, 2, 429-434
http://dx.doi.org/10.4236/ojs.2012.24053 Published Online October 2012 (http://www.SciRP.org/journal/ojs)
The Association of Hepatitis B Vaccine Supply Policy with
Timing of Receipt of the First Dose of Hepatitis B
Vaccination
Zhen Zha o1, Trudy V. Murphy2
1National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, USA
2National Center for HIV/AIDS, Viral Hepatitis, STD&TB Prevention, Centers for Disease Control and Prevention, Atlanta, USA
Received July 11, 2012; revised August 14, 2012; accepted August 26, 2012
ABSTRACT
An estimated 800,000 - 1.4 million persons in the US have chronic Hepatitis B Virus (HBV) infection. The risk for
chronic infection is greatest among young children; approximately 90% of infants will remain chronically infected with
HBV. Approximately 25% of those who become chronically infected during childhood die prematurely from cirrhosis
or liver cancer. Hepatitis B vaccination is the most effective measure to prevent HBV infection and its consequences. In
2006, 29 US states had Hepatitis B Vaccine Supply (HBVS) policy which either supplies hepatitis B vaccine at no cost
to all providers for all children or provides hepatitis B vaccine to delivery hospitals-only free of charge for all infants;
other 21 US states and the District of Columbia did not have. 17,636 infants born in 2006 obtained from 2007-2009
National Immunization Survey (NIS) were analyzed with survival analysis procedures of Kaplan-Meier estimate and
Cox proportional hazards model for complex sample survey to evaluate the association between state HBVS policy and
the timing of infant age in days to receipt of hepatitis B vaccination. State HBVS policy is associated with infant age in
days from birth to receipt of the first dose of hepatitis B vaccine (P < 0.01), and to completion of the 3-dose hepatitis B
vaccine series (P < 0.01). Receipt of the first dose of hepatitis B vaccine occurred 31% earlier among infants residing in
states with HBVS policy than among infants residing in states without (adjusted hazards ratio 1.31, 95%CI (1.23, 1.39)).
Completion of the 3-dose hepatitis B vaccine series were 12% sooner among infants living in states with HBVS policy
than among infants living in states without (adjusted hazards ratio 1.12, 95%CI (1.06, 1.18)). State HBVS policy may
help overcome barriers to timely delivery of hepatitis B vaccines to infants.
Keywords: First Dose Hepatitis B Vaccine; 3-Dose Hepatitis B Vaccine Series; Vaccine Supply Policy; Vaccination
Coverage; Cox Proportional Hazards Model
1. Introduction
An estimated 800,000 - 1.4 million persons in the US
have chronic hepatitis B virus (HBV) infection. The risk
for chronic infection is greatest among young children;
approximately 90% of infants will remain chronically
infected with HBV. By contrast, about 95% of adults
recover completely from HBV infection and do not be-
come chronically infected. Approximately 25% of those
who become chronically infected during childhood die
prematurely from cirrhosis or liver cancer [1]. Hepatitis
B vaccination is the most effective measure to prevent
HBV infection and its consequences. Completion of
hepatitis B immunization alone, when started within the
first day of life, prevents 70% - 95% of perinatal HBV
infections, as well as early childhood HBV infections
acquired from HBV-infected household contacts [2]. In
1991, the Advisory Committee on Immunization Prac-
tices (ACIP) proposed, for the first time, that hepatitis B
vaccination be recommended for all infants regardless of
the hepatitis B surface antigen (HBsAg) status of the
mother [3]. The preferred vaccination schedule of the
ACIP and the American Academy of Pediatrics (AAP)
calls for administering the first dose of hepatitis B vac-
cine during the newborn period, before the infant is dis-
charged from the hospital; the second dose at age 1 to 2
months; and the third dose at age 6 to 18 months [3-5].
The critical feature of the recommendation is to initiate
the 3-dose hepatitis B vaccine series at birth.
In the US, a state vaccine financing policy describes
which groups of children and in which settings the state
will purchase vaccine with Vaccines for Children (VFC)
program funds, Public Health Service Section 317 Im-
munization Grants Program funds, or state funds. The
state vaccine financing policies range from very com-
C
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Z. ZHAO, T. V. MURPHY 430
prehensive approaches, such as a Universal vaccine fi-
nancing policy, in which the state provides all vaccines
to all providers for all children, to approach in which the
state only provides vaccines for those children who are
VFC eligible [6,7].
The uptake of heptavalent pneumococcal conjugate
vaccine (PCV7) among children aged 19 to 35 months
residing in the United States and how uptake rates dif-
fered by state vaccine financing policy were evaluated
with logistic regression [7].
The research letter [8] suggested that the median of
hepatitis B birth dose vaccination rate might be higher
for infants with than without specific hospital hepatitis B
vaccine supply policy. The birth dose of hepatitis B vac-
cination status (yes vs. no) was defined as the first dose
of hepatitis B vaccine administered within 2 days of life
for infants born in 2002. Due to the data limitation, non-
parametric Wilcoxon rank-sum test was applied to com-
pare the median of hepatitis B birth dose vaccination
rates between the two independent groups. Thus that
analysis couldn’t account for the critical timing informa-
tion of infant age in days from birth to receipt of the first
dose of hepatitis B vaccine, and might compromise the
precision of the estimate and inference for the effect of
specific hospital hepatitis B vaccine supply policy. In
addition, the association of specific hospital hepatitis B
vaccine supply policy with completion of the 3-dose
hepatitis B vaccine series was not evaluated.
Robust data were lacking with regard to the associa-
tion between timing of infants age in days to receipt of
hepatitis B vaccination and state Hepatitis B Vaccine
Supply (HBVS) policy which will be defined in Section
2.2. In this study, we conducted a birth year cohort study
with infants born in 2006 obtained from 2007-2009 Na-
tional Immunization Survey (NIS). The primary objec-
tive of this study is to evaluate the association of state
HBVS policy with timing of infant age in days from birth
to receipt of the first dose of hepatitis B vaccine. The
secondary objective is to assess whether state HBVS
policy is associated with earlier completion of the 3-dose
hepatitis B vaccine series. In order to achieve the above
two objectives, survival analysis for complex sample
survey data was applied in this study.
2. Materials and Methods
2.1. Data Resource
A cohort of infants born in 2006 in the US was analyzed
in this study. Information about this birth cohort was
obtained from NIS conducted during 2007-2009. The
NIS is carried out annually by the Centers for Disease
Control and Prevention (CDC) to acquire national, state,
and selected urban-area estimates of vaccination cover-
age for the US non-institutionalized population of chil-
dren age 19 - 35 months [9]. For NIS 2007-2009 data, the
overall household response rates based on Council of
American Survey and Research Organizations (CASRO)
guidelines ranged from 63.2% to 64.9% [10]. The analy-
ses in this study were limited to children with adequate
provider data, children for whom sufficient vaccination
history information is obtained from their providers to
determine whether they are up-to-date with respect to the
recommended vaccination schedule, the proportions of
children with adequate provider data ranged from 85.4%
to 87.6% [10]. In the 2006 birth cohort, there were
17,636 infants that represented approximate 4.3 million
infants born in the US in 2006.
The socio-demographic factors related to infants, fam-
ily, mother, and vaccination provider available in the NIS
were examined in both univariate and multivariable
analyses. Those factors have previously been found to be
associated with infant vaccination coverage in the United
States [11-13]: infant race/ethnicity (Non-Hispanic White,
Non-Hispanic Black, Hispanic, other), first born status
(yes vs. no), and number of siblings (0 vs. ≥1); family
poverty status (at or above vs. below poverty level), and
locality (urban, suburban, rural); mother’s education level
(≤12 years vs. >12 years), marital status (married vs. not
married), and mother’s age (≤29 years vs. ≥30 years);
number (1 vs. ≥2) and type (public, private, other) of
vaccination providers; and survey interview language
(English, Spanish, or other).
2.2. State Hepatitis B Vaccine Supply (HBVS)
Policy
In the US, a state vaccine financing policy was self-re-
ported by the state immunization program to the National
Center for Immunization and Respiratory Diseases, Cen-
ters for Disease Control and Prevention. The states were
defined by their vaccine financing policy category: Uni-
versal; Universal-Select; VFC and Underinsured; VFC
and Underinsured-Select; VFC-Only; and Other [6,7,14].
The states with Universal or Universal-Select policy
supply hepatitis B vaccine among others at no cost to all
vaccination providers for all children, in 2006 sixteen
states were in this category (Alaska, New Hampshire,
New Mexico, Rhode Island, Vermont, Washington, Con-
necticut, Hawaii, Idaho, Maine, Massachusetts, Nevada,
North Carolina, North Dakota, South Dakota, and Wyo-
ming). In addition, some states have established a spe-
cific hospital hepatitis B vaccine supply policy that pro-
vides hepatitis B vaccine to delivery hospitals-only free
of charge for all infants regardless of the eligibility for
VFC or the health insurance status of infants [8]. In 2006,
thirteen states were in this category (Arizona, Arkansas,
Kansas, Kentucky, Louisiana, Michigan, Montana, New
York, Ohio, Oregon, Pennsylvania, Utah, and Wisconsin).

Z. ZHAO, T. V. MURPHY 431
Data on state specific hospital hepatitis B vaccine supply
policy were obtained from CDC’s Perinatal Hepatitis B
Prevention Program Annual Assessment Report for year
2006; this is the most recent information available on
state specific hospital hepatitis B vaccine supply policy.
To explore the association of hepatitis B vaccine sup-
ply policy with infant hepatitis B vaccination, in this
study, the preceding two types of policies together are
defined as state Hepatitis B Vaccine Supply (HBVS)
policy. Thus, in 2006 in the US, 29 US states had state
HBVS policy; and 21 US states and the District of Co-
lumbia did not have state HBVS policy.
2.3. Statistical Analyses
Survival analysis procedures for complex sample survey
[15] were adopted to evaluate the association of state
HBVS policy defined above with timing of infant hepati-
tis B vaccination. In the primary analysis, the “time” de-
pendent variable was defined as infant age in days from
birth to receipt of the first dose of hepatitis B vaccine.
The unprecedented feature of the recommended hepatitis
B vaccination schedule by ACIP and AAP is to initiate
hepatitis B vaccine series at birth, thus in this study if
infant age in days from birth to the first dose of hepatitis
B vaccination was less than or equal to 30 days then this
age was defined as an event, otherwise the age was right
censored at 30 days [5,16]. As for completion of the
3-dose hepatitis B vaccine series, by the recommended
schedule the third dose of hepatitis B vaccine should be
administered at least 112 days (16 weeks) after the first
dose and completed by 549 days (18 months) of age.
Thus in the secondary analysis, infants whose age being
greater than or equal to 112 days were included, and if
infant age in days from birth to the third dose of hepatitis
B vaccination was less than or equal to 549 days, then
the age was defined as an event, otherwise the age was
right censored at 549 days.
The two cumulative vaccination coverage curves for
the first dose of hepatitis B vaccination were estimated
with the use of Kaplan-Meier model by infant age in
days and stratified by state HBVS policy status (yes vs.
no), and were compared with the use of log-rank test.
Similarly, the cumulative vaccination coverage curve
estimation and comparison for completion of the 3-dose
hepatitis B vaccine series applied. The Cox proportional
hazards model [17,18] was applied to evaluate the asso-
ciation of state HBVS policy with infant age in days
from birth to receipt of the first dose of hepatitis B vac-
cine, also to completion of the 3-dose hepatitis B vaccine
series, controlling for the selected socio-demographic
factors. The backward-selection method [19,20] was ap-
plied to obtain the final model which contains the sig-
nificant predictors. The proportional hazards assumptions
of Cox model for NIS 2006 birth cohort data were ex-
amined by the graphic method, and were found to be
valid for all factors investigated.
3. Results
3.1. Prevalence Rates of State HBVS Policy
The prevalence rates of state HBVS policy across all
strata of the significant socio-demographic factors, which
were obtained in the final Cox model for evaluating the
association of state HBVS policy with infant age in days
from birth to receipt of the first dose of hepatitis B vac-
cine controlling for the selected socio-demographic fac-
tors, ranged from 26.9% to 46.9%, and the national rate
was 38.8%, as presented in Tab le 1. The prevalence rate
for Non-Hispanic White infants, 46.9%, was the highest
among all segments of race/ethnicity factor, and it was
significantly higher (p < 0.05) than the prevalence rate
for Non-Hispanic Black infants. The prevalence rate for
Hispanic infants, 26.9%, was the lowest (p < 0.05)
among all groups in race/ethnicity factor. Factor race/
ethnicity was significantly associated with state HBVS
policy status (p < 0.01). Infants whose mother’s educa-
tion >12 years were more likely than those whose
mother’s education ≤12 years to be residing in states
with HBVS policy (p < 0.01). Infants who had 1 vacci-
nation provider were more likely than those with ≥2
vaccination providers to live in HBVS policy states (p =
0.02).
3.2. The Association of State HBVS Policy with
the First Dose of Hepatitis B Vaccination
Two curves for the first dose of hepatitis B cumulative
vaccination coverage by infant age in days stratified by
state HBVS policy status were shown in Figure 1. Over-
all, the cumulative vaccination coverage for the first dose
of hepatitis B vaccine was significantly higher for infants
living in states with HBVS policy than infants living in
states without such policy (p-value < 0.01 by the log-
rank test). Table 2 presented the hepatitis B first dose
cumulative vaccination coverage with 95% confidence
interval at infant age 0 through 3 days, and 1 through 4
weeks for all infants and stratified by state HBVS policy
status. At each specific infant age, infants residing in
states with HBVS policy would be most likely (p-value <
0.05) to receive the first dose of hepatitis B vaccine
compared to infants residing in states without such pol-
icy.
The main effect of state HBVS policy was signifi-
cantly associated with infant age in days from birth to
receipt of the first dose of hepatitis B vaccine (p-value <
0.01, F-test) controlling for the six significant covariates
acquired from the Cox model. Receipt of the first dose of
hepatitis B vaccine occurred significantly earlier among
infants living in states with HBVS policy than among

Z. ZHAO, T. V. MURPHY 432
Table 1. Prevalence rates of state Hepatitis B Vaccine Sup-
ply (HBVS) policy by selected socio-demogr aphic fact or s.
Factor N Weighted % (95%CI)p-value
Total 17,636 38.8 (38.1, 39.5)
Race/ethnicity of infant
Non-Hispanic white 10,886 46.9 (45.7, 48.2)
Non-Hispanic black 1785 32.5 (29.3, 35.7)
Hispanic 3281 26.9 (24.9, 29.0)
Other 1684 39.1 (35.4, 42.9)
<0.01
Mother’s education
≤12 years 5208 36.8 (35.1, 38.5)
>12 years 12,428 40.9 (40.0, 41.9)
<0.01
Type of vaccination
provider
Private 11,207 38.3 (37.2, 39.4)
Public 1896 37.1 (33.7, 40.6)
Other 4372 40.9 (38.4, 43.3)
0.20
Number of
vaccination providers
1 12,118 39.8 (38.73, 40.92)
≥2 5485 36.8 (34.86, 38.69)
0.02
First born status
of infant
No 9330 37.8 (36.4, 39.1)
Yes 8306 40.0 (38.6, 41.5)
0.07
Mother’s age
≤29 years 6198 38.8 (37.0, 40.7)
≥30 years 11,438 38.8 (37.7, 39.9)
0.98
80%
70%
60%
50%
40%
30%
20% 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Age in days
HBVS Policy = YesHBVS Policy = No
Figure 1. Cumulative vaccination coverage in percentage
for the first dose of Hepatitis B (HepB) vaccine by infant
age in days stratified by state Hepatitis B Vaccine Supply
(HBVS) policy status.
Table 2. Cumulative vaccination coverage for the first dose
of Hepatitis B (HepB) vaccine by infant age in days/weeks
stratified by state Hepatitis B Vaccine Supply (HBVS) pol-
icy status.
Infant
Age
All Infants
%(95%CI)
HBVS Policy = Yes
%(95%CI)
HBVS Policy = No
%(95%CI)
0 day34.5 (33.3, 35.8)37.4 (35.8, 39.0) 32.7 (30.9, 34.5)
1 day50.6 (49.3, 51.9)56.3 (54.7, 57.9) 47.0 (45.1, 48.9)
2 days57.2 (55.9, 58.5)64.4 (62.8, 65.9) 52.7 (50.8, 54.6)
3 days58.7 (57.4, 60.0)65.8 (64.3, 67.4) 54.2 (52.3, 56.1)
1 week61.9 (60.6, 63.2)68.9 (67.4, 70.3) 57.5 (55.7, 59.4)
2 weeks64.5 (63.2, 65.8)70.9 (69.4, 72.3) 60.4 (58.6, 62.3)
3 weeks65.9 (64.6, 67.1)71.8 (70.3, 73.2) 62.1 (60.3, 64.0)
4 weeks66.7 (65.4, 67.9)72.3 (70.8, 73.7) 63.2 (61.3, 65.0)
infants living in states without such policy (adjusted haz-
ards ratio 1.31, 95%CI (1.23, 1.39)); significantly earlier
among Non-Hispanic Black infants than among Non-
Hispanic White infants (adjusted hazards ratio 1.16,
95%CI (1.04, 1.29)); and significantly sooner among
infants having multiple vaccination providers than among
infants having only 1 vaccination provider (adjusted haz-
ards ratio 1.25, 95%CI (1.17, 1.35)) as presented in Ta-
ble 3. In addition, the result acquired by unadjusted Cox
model were consistent with the result obtained from the
adjusted Cox model with regard to the significance status
of state HBVS policy measured by hazards ratios.
3.3. The Association between Completion of the
3-Dose Hepatitis B Vaccine Series and State
HBVS Policy
The two cumulative vaccination coverage curves for
completion of the 3-dose hepatitis B vaccine series by
infant age in days stratified by state HBVS policy status
were estimated and compared. In general, the cumulative
vaccination coverage for completion of the 3-dose hepa-
titis B vaccine series was significantly higher among
infants living in states with HBVS policy than among
infants living in states without such policy (p-value <
0.01 by the log-rank test).
The main effect of state HBVS policy was signifi-
cantly associated with infant age in days from birth to
completion of the 3-dose hepatitis B vaccine series
(p-value < 0.01, F-test) controlling for other six signifi-
cant predictors obtained from the Cox model. The adjusted
hazards ratio for state HBVS policy 1.12, with 95%CI (1.06,
1.18), suggested that completion of the 3-dose hepatitis B
vaccine series was significantly sooner among infants
residing in states with HBVS policy than among infants
residing in states without such policy. Infants who

Z. ZHAO, T. V. MURPHY 433
Table 3. Hazards Ratio (HR) of infant age in days from
birth to receipt of the first dose of hepatitis B vaccine be-
tween strata of state Hepatitis B Vaccine Supply (HBVS)
policy and the significant socio-demographic factors.
Factors
Unadjusted
HR
(95%CI)
Multivariable
Adjusted HR
(95%CI)
State Hepatitis B Vaccine Supply
(HBVS) policy status
Yes 1.28
(1.20, 1.36)
1.31
(1.23, 1.39)
No 1.00 1.00
Race/ethnicity of infant
Non-Hispanic white 1.00 1.00
Non-Hispanic black 1.14
(1.02, 1.26)
1.16
(1.04, 1.29)
Hispanic 1.09
(1.00, 1.18)
1.09
(1.00, 1.19)
Other 1.15
(1.03, 1.29)
1.17
(1.05, 1.30)
Mother’s education
≤12 years 1.13
(1.06, 1.21)
1.08
(1.01, 1.16)
>12 years 1.00 1.00
Type of vaccination providers
Private 1.01
(0.89, 1.13)
1.09
(0.96, 1.23)
Public 1.00 1.00
Other 1.19
(1.05, 1.36)
1.16
(1.02, 1.32)
Number of vaccination providers
1 1.00 1.00
≥2 1.29
(1.20, 1.38)
1.25
(1.17, 1.35)
First born status of infant
No 1.00 1.00
Yes 0.96
(0.90, 1.03)
0.94
(0.88, 1.00)
Mother’s age
≤29 years 1.16
(1.08, 1.24)
1.11
(1.03, 1.19)
≥30 years 1.00 1.00
had 0 sibling were significantly earlier than infants who
had 1 or more siblings with respect to completion of the
3-dose hepatitis B vaccine series (adjusted hazards ratio
1.13, 95%CI (1.06, 1.21)). Also, the significance status
of state HBVS policy gained by unadjusted Cox model,
(hazards ratio 1.11, 95%CI (1.05, 1.17)), was consistent
with the result achieved from the adjusted Cox model,
(hazards ratio 1.12, 95%CI (1.06, 1.18)).
4. Discussion
In our current study, both the unadjusted and adjusted
analyses showed the consistent conclusions: infant age in
days from birth to receipt of the first dose of hepatitis B
vaccine was significantly associated with state HBVS
supply policy, hazards ratios are 1.28 (1.20, 1.36) and
1.31 (1.23, 1.39) respectively. Similarly, consistent and
significant results were obtained with regard to the asso-
ciation between infant age in days from birth to comple-
tion of the 3-dose hepatitis B vaccine series and state
HBVS policy, hazards ratios are 1.11 (1.05, 1.17) and
1.12 (1.06, 1.18) for unadjusted and adjusted analysis
separately. These consistent results suggested that the
association between hepatitis B vaccination and state
HBVS policy is both positive and robust.
This study suggested that state HBVS policy was sig-
nificantly associated with infant age in days from birth to
receipt of the first dose of hepatitis B vaccine. Infants
residing in states with HBVS policy received the first
dose of hepatitis B vaccine significantly early than those
residing in states without such policy. For example,
56.3% of infants with state HBVS policy received the
first dose of hepatitis B vaccine by age 1 day; however
56.0% of infants without state HBVS policy received the
first dose of hepatitis B vaccine by age 5 days. Similarly,
infants completed the 3-dose of hepatitis B vaccine series
significantly sooner among infants with state HBVS pol-
icy than among infants without such policy. For instance,
82.8% of infants with state HBVS policy completed the
3-dose hepatitis B vaccine series by age 10 months; but
82.8% of infants without such policy completed the
3-dose hepatitis B vaccine series by age 11.3 months.
This study showed that the first dose of hepatitis B
vaccine was administered significantly earlier among
infants residing in states with HBVS policy, which is
important. However, it is also important to know if state
HBVS policy is associated with earlier completion of the
3-dose hepatitis B vaccine series. As the secondary ob-
jective, this study suggested that state HBVS policy is
associated with earlier completion of the 3-dose hepatitis
B vaccine series. The significant and positive answer
strengthens the argument for state HBVS supply policy.
Some potential limitations of this study were that the
NIS used the random-digit-dial residential landline tele-
phone survey and has experienced under-representation
due to non-response and wireless telephone use. Al-
though the survey has been adjusted to account for these
changes, under-representation of households could in-
crease the potential bias in survey estimates. Also, non-
response bias after weighting adjustments and possible
incomplete ascertainment of hepatitis B vaccination by
provider record check may cause additional bias. Finally,
a few sub-state estimation areas rotated in or out in the
survey design during the last few years. However a re-
cent study [21] suggested that the total survey error in the
NIS may be small with a mean of 1.7%, 95%CI (1.71%,

Z. ZHAO, T. V. MURPHY 434
1.74%), and would likely not have changed the conclu-
sions in this study.
5. Conclusion
State HBVS policy has significantly improved access to
hepatitis B vaccine for infants in the US. This policy re-
sults in earlier first dose of hepatitis B vaccination, such
as before discharge from the delivery hospital or birthing
center, sooner completion of the 3-dose hepatitis B vac-
cine series, and higher hepatitis B vaccination coverage.
State HBVS policy may help overcome barriers to timely
delivery of hepatitis B vaccines to infants.
6. Disclaimer
The findings and conclusions in this article are solely the
responsibility of the authors and do not necessarily rep-
resent the official views of Centers for Disease Control
and Prevention.
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