OBJECTIVES:

Pregnant women routinely receive information in support of or opposing infant immunization. We aimed to describe immunization information sources of future mothers’ and determine if receiving immunization information is associated with infant immunization timeliness.

METHODS:

We analyzed data from a child cohort born 2009–2010 in New Zealand. Pregnant women (N = 6822) at a median gestation of 39 weeks described sources of information encouraging or discouraging infant immunization. Immunizations received by cohort infants were determined through linkage with the National Immunization Register (n = 6682 of 6853 [98%]). Independent associations of immunization information received with immunization timeliness were described by using adjusted odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS:

Immunization information sources were described by 6182 of 6822 (91%) women. Of these, 2416 (39%) received information encouraging immunization, 846 (14%) received discouraging information, and 565 (9%) received both encouraging and discouraging information. Compared with infants of women who received no immunization information (71% immunized on-time), infants of women who received discouraging information only (57% immunized on time, OR = 0.49, 95% CI 0.38–0.64) or encouraging and discouraging information (61% immunized on time, OR = 0.51, 95% CI 0.42–0.63) were at decreased odds of receiving all immunizations on time. Receipt of encouraging information only was not associated with infant immunization timeliness (73% immunized on time, OR = 1.00, 95% CI 0.87–1.15).

CONCLUSIONS:

Receipt, during pregnancy, of information against immunization was associated with delayed infant immunization regardless of receipt of information supporting immunization. In contrast, receipt of encouraging information is not associated with infant immunization timeliness.

What’s Known on This Subject:

Future parents receive information about immunization from multiple sources. Some of this information encourages immunization, whereas some discourages immunization. It is unknown whether antenatal receipt of information about immunization is associated with the timeliness of infant immunization.

What This Study Adds:

During pregnancy, health professionals are the main source of encouraging information about infant immunization, with family and friends being the main source of discouraging information. Receiving discouraging information increases the odds of delayed infant immunization. Encouraging information is not associated with immunization timeliness.

Timely immunization is necessary for national immunization programs to provide full-population health benefit. Timeliness is particularly important for the primary infant immunization series. Delayed receipt of any of these vaccine doses increases the risk of hospital admission during infancy with vaccine-preventable disease.1,2 

Most future parents make their decisions regarding the immunization of their infant before that child’s birth.3,5 Parental immunization decision-making is influenced by information they received, which comes from many sources, including family and friends, health care providers, and the media.6 The information received can either encourage or discourage infant immunization. The effect of this differing information on infant immunization timeliness is unknown. In particular, it is unknown whether receiving encouraging information increases or receiving discouraging information decreases the likelihood of timely immunization.

Our objectives were to describe the sources of encouraging and discouraging information about immunization that are received by pregnant women and to determine if receipt of such information is associated with the timeliness of infant immunization. We hypothesized that receipt of encouraging information would be associated with more timely immunization and that receipt of discouraging information would be associated with less timely immunization.

We completed this project within New Zealand’s (NZ) child cohort study, Growing Up in New Zealand (www.growingup.co.nz). This prospective cohort was established by recruiting pregnant women with an estimated delivery date between April 25, 2009, and March 25, 2010, who were residents in a geographically defined region of New Zealand chosen for its population diversity.7 There were no exclusion criteria. Eleven percent of all children born in NZ during the recruitment period were enrolled. The enrolled cohort is generalizable to all births in NZ from 2007 to 2010.8 The Growing Up in New Zealand cohort was designed to have adequate explanatory power to undertake complex longitudinal analyses, both across the whole cohort and within ethnic and socioeconomic subgroups.7 Ethical approval was from the NZ Ministry of Health Ethics Committee. All enrolled women provided written, informed consent. They were informed at enrollment that their enrolled children would be followed in the study at least until they were 18 years old.

Growing Up in New Zealand recruited 6822 women and their 6853 children.7 For the present analysis, we limited the sample to the 6182 (91%) women who were enrolled antenatally and their 6205 (91%) children. For the 168 multiple births in the cohort, we only included the first-born child in these analyses. For all but 3 sets of twins or triplets, immunization coverage and timeliness were identical between twin or triplet siblings.

Each participant completed a computer-assisted, face-to-face enrollment interview. This interview was completed at a median gestation of 39 (interquartile range of 38–40) weeks, with 345 (6%) of the women interviewed before 37 weeks gestation.7 

Each woman was asked if she had decided yet if she would have her child immunized (published previously).9 We then asked if she had received any information encouraging her or discouraging her to immunize her child during infancy (Fig 1). For both encouraging and discouraging information, each woman identified all sources of the immunization information. We provided response options that included general information sources and those specific to pregnancy. The response options offered were as follows: family, friends, the family doctor, midwife, obstetrician, dietician or nutritionist, alternative health care practitioner, antenatal class, the Internet, radio, television, printed media, or other sources (Fig 1). In NZ, pregnant women choose between one of several types of pregnancy health care providers, including a family doctor (general practitioner), midwife, or obstetrician; the majority of women have a midwife as their main pregnancy health care provider.10 Antenatal class attendance is encouraged but not mandatory.

FIGURE 1

Questions asked of expectant mothers at the Growing Up in New Zealand antenatal interview regarding whether they received information encouraging and/or discouraging them to immunize their expected children and the sources of the information.

FIGURE 1

Questions asked of expectant mothers at the Growing Up in New Zealand antenatal interview regarding whether they received information encouraging and/or discouraging them to immunize their expected children and the sources of the information.

Close modal

Each infant’s immunization information was obtained from the National Immunization Register (NIR).11 We established linkage by using the National Health Index number, which is a unique identifier assigned to every person having contact with health care services in NZ. Consent for NIR linkage was obtained for 6682 (98%) of the enrolled infants, with linkage established (ie, an infant’s National Health Index number identified in the NIR) for 6674 (97%).

When the children in the cohort were infants, the NZ immunization schedule included 6-week, 3-month, and 5-month doses of the following 2 vaccines: 1 with diphtheria-tetanus-acellular pertussis, Haemophilus influenzae type B, hepatitis B, and poliovirus antigens; and the pneumococcal conjugate vaccine.12 We defined timely immunizations as those received within 30 days of their recommended date.9,13,15 We used the following 3 measures of immunization timeliness: (1) all immunizations received on time as the primary outcome, (2) the first set of immunizations (2 vaccines) was received on time, and (3) no immunizations were received on time. Timely receipt of the first set of immunizations was included as 1 of the measures of timeliness because of its strong association with delay in subsequent immunizations.16 

Maternal socioeconomic status and education were described by using measures from Statistics NZ’s 2006 national census and 2008 General Social Survey.17,18 Area-level socioeconomic deprivation was measured by using the 2006 NZ Index of Deprivation grouped as quintiles.19 The 2006 NZ Index of Deprivation, which is derived from 2006 census data on 9 socioeconomic characteristics, is a well-validated, small-area measure of socioeconomic deprivation in NZ.19 

For analysis purposes, the immunization information sources were combined into the following 3 groups: family and friends, health care, and media.

We described the proportion of women receiving encouraging and/or discouraging information about immunization from all sources. We described associations of maternal and household demographics, which are known to be associated with immunization timeliness,14 with receipt of only encouraging, both encouraging and discouraging, or only discouraging information. We grouped all health care providers into 1 category because in NZ, child health care is sought from a wide variety of care providers, and families seek care from alternative health care providers as an adjunct rather than an alternative to conventional health care.20 By using multivariable logistic regression, we examined associations with immunization timeliness of receiving only encouraging, both encouraging and discouraging, or only discouraging information. These analyses were reported by using adjusted odds ratios (OR), 95% confidence intervals (CIs), and by using SAS version 9.2 (SAS Institute, Cary, NC). A 2-sided P value of <.05 was considered statistically significant.

Receipt of encouraging or discouraging information was reported by 6158 (99%) of the women interviewed, with 1846 (30%) receiving only encouraging information, 565 (10%) receiving both encouraging and discouraging information, 280 (4%) receiving only discouraging information, and 3467 (56%) recalled receiving no information about immunization (Fig 2).

FIGURE 2

Study recruitment, antenatal interview, and the expectant mothers’ receipt of encouraging and/or discouraging information about infant immunization during the current pregnancy.

FIGURE 2

Study recruitment, antenatal interview, and the expectant mothers’ receipt of encouraging and/or discouraging information about infant immunization during the current pregnancy.

Close modal

Two or more encouraging information sources were identified by 1158 of the 2411 (48%) women who received encouraging information and ≥2 discouraging information sources were identified by 336 of the 845 (40%) women who received discouraging information.

Of the 6158 women interviewed, immunization information was received from family and friends by 872 (14%), health care providers by 2174 (35%), media by 835 (14%), and other sources by 119 (2%) (Fig 3). Most who identified health care providers as an information source (90%) received only encouraging information. In contrast, 39% of those identifying family and friends as an information source received only encouraging information, and 53% of those identifying media sources received only encouraging information (Fig 3).

FIGURE 3

Number of pregnant women (n = 6158) receiving information encouraging immunization, discouraging immunization, or both from family and friends, health care providers, or media.

FIGURE 3

Number of pregnant women (n = 6158) receiving information encouraging immunization, discouraging immunization, or both from family and friends, health care providers, or media.

Close modal

Immunization information received was encouraging only for a larger proportion of those who received this from family (68%) compared with friends (42%) (Table 1). Whereas almost all immunization information from the family doctor (98%), midwife (94%), or obstetrician (97%) was encouraging only, this was not the case for the smaller numbers of pregnant women who received immunization information from a dietician or nutritionist (40% encouraging only) or alternative health care provider (18% encouraging only) (Table 1). Maternal ethnicity, parity, education, household deprivation, and whether a woman was decided about immunizing her expected child were each independently associated with the type of immunization information received (Table 2).

TABLE 1

Pregnant Women’s Sources of Antenatal Information Encouraging or Discouraging Infant Immunization

Source of Immunization InformationnType of Information Received Antenatally About Infant Immunizations
Encouraging Information OnlyEncouraging and Discouraging InformationDiscouraging Information OnlyP
n = 1846n = 565n = 280
n (Row %)n (Row %)n (Row %)
Family and friends Total = 872    <.001a 
 Family 551 373 (68) 38 (7) 140 (25)  
 Friends 560 234 (42) 51 (9) 275 (49)  
Health care providers Total = 2174    <.001b 
 Family doctor (general practitioner) 883 860 (98) 12 (1) 11 (1)  
 Midwife 1542 1444 (94) 68 (4) 30 (2)  
 Obstetrician 85 82 (97) <10 (2) <10 (1)  
 Dietician or nutritionist <10 <10 (40) 0 (0) <10 (60)  
 Alternative health care practitioner 61 11 (18) <10 (7) 46 (75)  
 Antenatal class 327 260 (79) 52 (16) 15 (5)  
Media Total = 835    <.001b 
 Internet 237 89 (38) 36 (15) 112 (47)  
 Radio 82 62 (76) <10 (1) 19 (23)  
 Television 345 200 (58) 27 (8) 118 (34)  
 Books, magazines, or newspaper 557 344 (62) 74 (13) 139 (25)  
Other Total = 119 48 (40) 9 (8) 62 (52)  
Source of Immunization InformationnType of Information Received Antenatally About Infant Immunizations
Encouraging Information OnlyEncouraging and Discouraging InformationDiscouraging Information OnlyP
n = 1846n = 565n = 280
n (Row %)n (Row %)n (Row %)
Family and friends Total = 872    <.001a 
 Family 551 373 (68) 38 (7) 140 (25)  
 Friends 560 234 (42) 51 (9) 275 (49)  
Health care providers Total = 2174    <.001b 
 Family doctor (general practitioner) 883 860 (98) 12 (1) 11 (1)  
 Midwife 1542 1444 (94) 68 (4) 30 (2)  
 Obstetrician 85 82 (97) <10 (2) <10 (1)  
 Dietician or nutritionist <10 <10 (40) 0 (0) <10 (60)  
 Alternative health care practitioner 61 11 (18) <10 (7) 46 (75)  
 Antenatal class 327 260 (79) 52 (16) 15 (5)  
Media Total = 835    <.001b 
 Internet 237 89 (38) 36 (15) 112 (47)  
 Radio 82 62 (76) <10 (1) 19 (23)  
 Television 345 200 (58) 27 (8) 118 (34)  
 Books, magazines, or newspaper 557 344 (62) 74 (13) 139 (25)  
Other Total = 119 48 (40) 9 (8) 62 (52)  
a

P value derived from an χ2 test.

b

P value derived from a Fisher-Freeman-Halton exact test.

TABLE 2

Association of Maternal and Household Characteristics With Antenatal Receipt of Information About Infant Immunization

Maternal and Household CharacteristicsnType of Information Received Antenatally About Infant Immunizations
Encouraging Information OnlyEncouraging and Discouraging InformationDiscouraging Information OnlyNo InformationPa
n = 1846n = 565n = 280n = 3467
(Column %)n (Row %)n (Row %)n (Row %)n (Row %)
Self-prioritized ethnicityb 6148     <.001 
 European 3312 (54) 714 (21) 387 (12) 201 (6) 2010 (61)  
 Māori 851 (14) 259 (30) 83 (10) 31 (4) 478 (56)  
 Pacific 875 (14) 447 (51) 43 (5) 14 (2) 371 (42)  
 Asian 889 (14) 367 (41) 32 (4) 22 (2) 468 (53)  
 Other 221 (4) 56 (25) 18 (8) 12 (6) 135 (61)  
Age group, y 6158     <.001 
 <20 302 (5) 123 (41) 20 (6) 9 (3) 150 (50)  
 20–29 2415 (39) 803 (33) 216 (9) 94 (4) 1302 (54)  
 30–39 3202 (52) 860 (27) 307 (10) 167 (5) 1868 (58)  
 >40 239 (4) 60 (25) 22 (9) 10 (4) 147 (62)  
Parity 6158     <.001 
 First child 2571 (42) 814 (32) 337 (13) 119 (5) 1301 (50)  
 Subsequent child 3587 (58) 1032 (29) 228 (6) 161 (5) 2166 (60)  
Pregnancy planning 6138     <.001 
 Planned 3705 (60) 1008 (27) 391 (11) 191 (5) 2115 (57)  
 Unplanned 2433 (40) 834 (34) 173 (7) 89 (4) 1337 (55)  
Education 6147     <.001 
 Primary 425 (7) 156 (37) 14 (3) 10 (2) 245 (58)  
 Secondary 1465 (24) 535 (36) 97 (7) 49 (3) 784 (54)  
 Tertiary 4257 (69) 1152 (27) 453 (11) 220 (5) 2432 (57)  
Household deprivationc 6156     <.001 
 1–2 (least deprived) 987 (16) 219 (22) 103 (11) 62 (6) 603 (61)  
 3–4 1130 (18) 265 (23) 121 (11) 59 (5) 685 (61)  
 5–6 1070 (17) 273 (26) 133 (12) 50 (5) 614 (57)  
 7–8 1273 (21) 434 (34) 90 (7) 61 (5) 688 (54)  
 9–10 (most deprived) 1696 (28) 655 (39) 118 (7) 48 (3) 655 (39)  
Infant immunization 6172     <.001 
 Decidedd 5399 (87) 1697 (32) 438 (8) 211 (4) 3035 (56)  
 Undecided 773 (13) 147 (19) 126 (16) 69 (9) 427 (56)  
Maternal and Household CharacteristicsnType of Information Received Antenatally About Infant Immunizations
Encouraging Information OnlyEncouraging and Discouraging InformationDiscouraging Information OnlyNo InformationPa
n = 1846n = 565n = 280n = 3467
(Column %)n (Row %)n (Row %)n (Row %)n (Row %)
Self-prioritized ethnicityb 6148     <.001 
 European 3312 (54) 714 (21) 387 (12) 201 (6) 2010 (61)  
 Māori 851 (14) 259 (30) 83 (10) 31 (4) 478 (56)  
 Pacific 875 (14) 447 (51) 43 (5) 14 (2) 371 (42)  
 Asian 889 (14) 367 (41) 32 (4) 22 (2) 468 (53)  
 Other 221 (4) 56 (25) 18 (8) 12 (6) 135 (61)  
Age group, y 6158     <.001 
 <20 302 (5) 123 (41) 20 (6) 9 (3) 150 (50)  
 20–29 2415 (39) 803 (33) 216 (9) 94 (4) 1302 (54)  
 30–39 3202 (52) 860 (27) 307 (10) 167 (5) 1868 (58)  
 >40 239 (4) 60 (25) 22 (9) 10 (4) 147 (62)  
Parity 6158     <.001 
 First child 2571 (42) 814 (32) 337 (13) 119 (5) 1301 (50)  
 Subsequent child 3587 (58) 1032 (29) 228 (6) 161 (5) 2166 (60)  
Pregnancy planning 6138     <.001 
 Planned 3705 (60) 1008 (27) 391 (11) 191 (5) 2115 (57)  
 Unplanned 2433 (40) 834 (34) 173 (7) 89 (4) 1337 (55)  
Education 6147     <.001 
 Primary 425 (7) 156 (37) 14 (3) 10 (2) 245 (58)  
 Secondary 1465 (24) 535 (36) 97 (7) 49 (3) 784 (54)  
 Tertiary 4257 (69) 1152 (27) 453 (11) 220 (5) 2432 (57)  
Household deprivationc 6156     <.001 
 1–2 (least deprived) 987 (16) 219 (22) 103 (11) 62 (6) 603 (61)  
 3–4 1130 (18) 265 (23) 121 (11) 59 (5) 685 (61)  
 5–6 1070 (17) 273 (26) 133 (12) 50 (5) 614 (57)  
 7–8 1273 (21) 434 (34) 90 (7) 61 (5) 688 (54)  
 9–10 (most deprived) 1696 (28) 655 (39) 118 (7) 48 (3) 655 (39)  
Infant immunization 6172     <.001 
 Decidedd 5399 (87) 1697 (32) 438 (8) 211 (4) 3035 (56)  
 Undecided 773 (13) 147 (19) 126 (16) 69 (9) 427 (56)  
a

P value derived from an χ2 test.

b

“Other” includes Middle Eastern, Latin American, and African.

c

Area-level socioeconomic deprivation was measured by using the NZ Index of Deprivation.19 

d

Whether each pregnant woman was decided about the immunization of her expected child.9 

In comparison with the infants of women who received no immunization information while pregnant, the infants of women who received discouraging information only were at decreased odds of having all immunizations (OR = 0.49, 95% CI 0.38–0.64) or their 6-week dose (OR = 0.39, 95% CI 0.29–0.53) on time and at increased odds of all of their immunizations being delayed (OR = 2.61, 95% CI 1.87–3.59) (Figs 46). The following associations of the receipt of discouraging information with all 3 measures of immunization timeliness were of similar magnitude if encouraging information had also been received: the odds of receiving all immunizations (OR = 0.51, 95% CI 0.42–0.63) or 6-week immunizations (OR = 0.45, 95% CI 0.35–0.58) on time; and the odds of all immunizations being delayed (OR = 2.70, 95% CI 2.08–3.50) (Figs 46). Receipt of discouraging information from any of the 3 specific sources (family and friends, health care, or media), either alone or with encouraging information, was also associated with decreased odds of receiving all infant immunizations (Fig 4) or the 6-week immunizations (Fig 5) on time and increased odds of all immunizations being delayed (Fig 6). In comparison with the infants of women who received no immunization information, receipt of encouraging information from any source was not associated with any of the infant immunization timeliness measures. This was also the case for encouraging information received from family and friends, health care or media sources (Figs 46).

FIGURE 4

Timeliness of all infant immunizations in association with maternal sources of infant immunization information received during pregnancy. a Multivariable analysis adjusted for maternal ethnicity, age, education, employment, pregnancy planning and parity, household deprivation, and whether each woman was undecided about her immunization intentions for her child when interviewed.

FIGURE 4

Timeliness of all infant immunizations in association with maternal sources of infant immunization information received during pregnancy. a Multivariable analysis adjusted for maternal ethnicity, age, education, employment, pregnancy planning and parity, household deprivation, and whether each woman was undecided about her immunization intentions for her child when interviewed.

Close modal
FIGURE 5

Timeliness of the 6-week infant immunizations in association with maternal sources of infant immunization information received during pregnancy. a Multivariable analysis adjusted for maternal ethnicity, age, education, employment, pregnancy planning and parity, household deprivation, and whether each woman was undecided about her immunization intentions for her child when interviewed.

FIGURE 5

Timeliness of the 6-week infant immunizations in association with maternal sources of infant immunization information received during pregnancy. a Multivariable analysis adjusted for maternal ethnicity, age, education, employment, pregnancy planning and parity, household deprivation, and whether each woman was undecided about her immunization intentions for her child when interviewed.

Close modal
FIGURE 6

Delay in receipt of all infant immunizations in association with maternal sources of infant immunization information received during pregnancy. a Multivariable analysis adjusted for maternal ethnicity, age, education, employment, pregnancy planning and parity, for household deprivation, and whether each woman was undecided about her immunization intentions for her child when interviewed.

FIGURE 6

Delay in receipt of all infant immunizations in association with maternal sources of infant immunization information received during pregnancy. a Multivariable analysis adjusted for maternal ethnicity, age, education, employment, pregnancy planning and parity, for household deprivation, and whether each woman was undecided about her immunization intentions for her child when interviewed.

Close modal

Less than half (44%) of this cohort of 6822 pregnant NZ women recalled receiving information, antenatally, about the immunization of their future children. Thirty percent of the pregnant women recalled receiving only information encouraging immunization, 10% received encouraging and discouraging information, and 4% received only discouraging information. Recall of receipt of discouraging information was associated with an increased likelihood of delayed infant immunization, as was both encouraging and discouraging information. There was no association between recall of receiving encouraging information and immunization timeliness. Health care providers were the most common source of immunization information (35%), and 90% of women received only encouraging information from health care sources. Sixty-three percent of the women in our study cited midwives as a source of immunization information, reflecting NZ’s predominantly midwife-led model of maternity care, where ∼80% of women select a midwife as their pregnancy health care provider.10 

This is the largest study to date in which researchers have examined maternal receipt of infant immunization information during pregnancy. The results are consistent with those of smaller studies. A US study found that 124 of 200 (62%) of expectant first-time mothers sought immunization information during the previous month of their pregnancy, with 73 (37%) of them receiving this information from their obstetrician or midwife.6 Unlike our study, this study had multiple exclusion criteria, including women who were younger than 18 years old, had multiple births, less than a high school education, poor English skills, no computer or mobile access, or had already decided not to immunize their infants. A Japanese study found that during an antenatal clinic visit, only 14 of 70 (20%) pregnant women discussed infant immunization with a health care professional.21 

Health care professionals (particularly doctors, midwives, and nurses) are a common and trusted source of infant immunization information.6,21,26 However, we found no association between the receipt of encouraging information from health care sources and immunization timeliness, which is consistent with a 2013 Cochrane review that concluded that antenatal face-to-face immunization education interventions had little or no effect on immunization status.27 More recently, researchers found that timely infant immunization was more likely if the mother received one-on-one antenatal immunization education.28,29 It will be important to determine if specifically immunization-focused education is sufficient to overcome the effect of any discouraging information received.

The relationship we observed between the receipt of discouraging information and delayed infant immunization is consistent with a previous NZ study, demonstrating that fewer children received timely immunizations in primary care practices where caregivers reported receiving information that discouraged immunization.30 However, this was a retrospective study, and therefore, it could not determine if caregivers received information before or after the children’s immunization. It is concerning that 18% of women who recalled receiving discouraging information identified health care providers as a source of this information because health care providers have a professional responsibility to promote immunization.

A novel finding from our study is that delayed infant immunizations are associated with the mother receiving both encouraging and discouraging immunization information during pregnancy. The ambiguity created by receiving both encouraging and discouraging information may be a key factor leading to parental vaccine hesitancy.31 Health care providers are likely to remain the main source of information that encourages infant immunization once the child is born. We suggest it may be necessary to identify those parents who have already received information that discourages them from immunizing their infants and develop immunization promotion strategies specific to this group.

Although we cannot prevent the exposure of pregnant women to information discouraging immunization, we can improve the delivery and investigate the effectiveness of interventions encouraging infant immunization. For information provided about immunization to be effective, it is important to determine the informational needs of the target population because these may vary between countries and by maternal demographics, such as parity or ethnicity. In the United States, for example, white and Hispanic parents were more likely than African-American parents to trust family and friends for vaccine-safety information.25 

Recent results from the Growing Up in New Zealand study indicate that first-time expectant mothers are more likely to be undecided about immunization than women who already had children.9 We observed that although women expecting their first child were more likely to receive information about infant immunization, approximately half (1301 of 2571; 51%) had not. There is a clear need to provide expectant first-time mothers with appropriate information during pregnancy to enable them to make informed decisions about their infants’ immunization.

This study has several strengths. It was completed within a large and nationally generalizable cohort7 by using an immunization registry to describe immunization timeliness.32 Our study context was broad, with immunization being only 1 of a wide range of research domains considered.7 Hence, there is less likelihood that participants would over- or underreport their immunization information sources than would be the case in an immunization-focused study. We only included women recruited antenatally, and only 345 (6%) were interviewed preterm. Thus, we believe we captured the majority of time during which pregnant women could have received immunization information. It is possible that women received some of the information they described before their pregnancy. However, because women in NZ identify a specific health care provider for their pregnancy, and our questions about immunization information asked women to identify these pregnancy-specific sources, we were able to create a pregnancy focus for our data collection.

The broad study scope limited our ability to investigate information sources in detail. We were not able to gather information on the specific sources used (eg, Web sites and social media), investigate the content of the encouraging versus discouraging messages, or quantify the exposure to different information types. Our observational study cannot establish whether exposure to discouraging information caused a delay in the receipt of infant immunizations. It is possible that women who had negative views about immunization actively sought discouraging information. People are more likely to remember information that is in line with their own opinions about an issue, and hence, this may have biased our estimates of what proportion of women received encouraging or discouraging information.33 Because of the specifics of the NZ health care system, particularly with regard to antenatal care, the results of our study may not be generalizable to other health care contexts.

During pregnancy, women who recalled receiving information discouraging immunization had an increased likelihood of delayed infant immunization regardless of whether they reported receiving encouraging information about immunization. In contrast, the receipt of encouraging information was not associated with infant immunization timeliness. Researchers in future studies should explore the content of the discouraging information and help develop counterarguments to offset what appears to be impactful information. Researchers in future studies might also investigate the quality of the information that encourages parents to immunize their future children and how best to promote the key child health messages that will enable timely infant immunization.

     
  • CI

    confidence interval

  •  
  • NIR

    National Immunization Register

  •  
  • NZ

    New Zealand

  •  
  • OR

    odds ratio

Dr Veerasingam analyzed and interpreted the data and completed the first and final drafts of the manuscript; Dr Grant contributed to the conception and design of the study, developed the data collection instruments, analyzed and interpreted the data, and edited the first and final drafts of the manuscript; Dr Chelimo analyzed and interpreted the data and edited the manuscript; Dr Philipson interpreted the data and edited the manuscript; Dr Gilchrist interpreted the data and edited first and final drafts of the manuscript; Dr Berry and Dr Atatoa Carr contributed to the conception and design of the study, developed the data collection instruments, interpreted the data, and edited the manuscript; Dr Camargo Jr contributed to the conception and design of the study, interpreted the data, and edited the manuscript; Dr Morton conceived and designed the cohort study, developed the data collection instruments, interpreted the data, and edited the manuscript; and all authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

FUNDING: Growing Up in New Zealand has been funded by the New Zealand Ministries of Social Development, Health, Education, Justice, and Pacific Island Affairs; the former Ministry of Science Innovation and the former Department of Labor (now both part of the Ministry of Business, Innovation, and Employment); the former Ministry of Women’s Affairs (now the Ministry for Women); the Department of Corrections; the Families Commission (now known as the Social Policy Evaluation and Research Unit); Te Puni Kokiri; New Zealand Police; Sport New Zealand; the Housing New Zealand Corporation; the former Mental Health Commission; The University of Auckland; and Auckland UniServices Limited. Other support for the study has been provided by the New Zealand Health Research Council, Statistics New Zealand, the Office of the Children’s Commissioner, and the Office of Ethnic Affairs. The Starship Foundation funded Dr Veerasingam.

Most importantly, we acknowledge the children and families who are part of the Growing Up in New Zealand study. We also acknowledge the initial funders, particularly the NZ Ministry of Social Development (supported by the Health Research Council of NZ), as well as the ongoing support from Auckland UniServices and The University of Auckland. The funders played no role in the design or conduct of the study; collection, management, analysis, or interpretation of the data; preparation, review, or approval of the manuscript; or the decision to submit the manuscript for publication. The authors of this article are members of the current research team, which includes the study director, associate directors, and the domain and theme experts. We acknowledge all the members of the Growing Up in New Zealand team, including those members and managers of the operational (in-person and computer-assisted telephone interviewing), data, communications, community, and quality aspects of the study. We acknowledge the ongoing support and advice provided by our Kaitiaki Group and our national and international Expert Scientific Advisory Group. We also acknowledge the members of the Morton Consortium who were responsible for planning and design this study in the development phase.

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Competing Interests

POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.

FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.