Association Between Influenza Vaccination During Pregnancy and Breastfeeding Duration

Abstract

Background:

Prenatal vaccination and breastfeeding are both health promotional behaviors. The benefits of breastfeeding are widely investigated and well established, as well as the effectivity and the safety of the influenza vaccination. This study aimed to investigate the association between the prenatal health behavior of influenza vaccination and breastfeeding duration for at least 3 months in the United States.

Methods:

A secondary data analysis was conducted using 2016–2019 Pregnancy Risk Assessment and Monitoring System data consisting of 83,976 postpartum women.

Results:

Overall, 68.3% (n = 57,269) breastfed for at least 3 months and 56.6% (n = 48,834) received the influenza vaccine during pregnancy. Women who did not receive the influenza vaccine during pregnancy were significantly less likely to breastfeed compared with women who received the vaccine during pregnancy (64.5% versus 71.1%; p < 0.001). Significant covariates associated with ≥3-month breastfeeding duration included maternal sociodemographic factors, infant factors, maternal health factors, and prenatal health behaviors. In the multivariable logistic regression analyses, the odds of breastfeeding at least 3 months were significantly lower in women who did not receive the influenza vaccine during pregnancy compared with those who were vaccinated (odds ratio, 0.92; 95% confidence interval, 0.88–0.98; p = 0.005).

Discussion:

Findings from this large, nationally representative sample of U.S. mothers indicate an association between the health-promotional behaviors of prenatal influenza vaccination and breastfeeding duration postpartum. Recommendations and education by health care providers should include a focus on maternal health behaviors to support positive maternal–infant health outcomes including reduced risk of infection and extended breastfeeding duration.

Introduction

To reduce the increased risk of severe infection, complications, and mortality associated with influenza, it is recommended that women who are pregnant, planning to become pregnant, and postpartum be vaccinated against influenza.^1–4 Maternal mortality rates from influenza were found to be higher among unvaccinated compared with vaccinated pregnant women.⁵ Findings from research studies have supported the safety of inactivated influenza vaccines in pregnant women⁶ and in breastfeeding mothers.⁷ An international pooled analysis demonstrated no association between maternal influenza vaccination and negative birth outcomes of low birthweight, preterm birth, and stillbirth.⁸ Furthermore, researchers found that specific immunoglobulin A (sIgA) antibody levels against influenza were higher in the milk of women who were vaccinated.⁹

Despite vaccination recommendations and the Healthy People 2020 national target goal of 80%, influenza vaccination rates among pregnant women before and during pregnancy have been consistently low at <40%, based on U.S. 2012–2016 data from the National Health Interview Survey.¹⁰ Using data from a smaller sample of 1,841 pregnant women in the United States who participated in an Internet panel survey, 61.2% reported receiving the influenza vaccine before or during pregnancy in 2018–2019.¹¹ Multiple factors have been found to be associated with vaccine uptake in pregnancy including race/ethnicity, education, insurance status, and health care provider recommendations.¹²

There are racial/ethnic disparities in vaccine uptake among pregnant women, with Black women having the lowest rates at 39.1% compared with non-Hispanic White at 49.8%, Hispanic at 51.5%, and Asian with the highest rate of 55.4%.¹³ Specific for African American adults, there is distrust of the health care system and government agencies regarding vaccines, contributing to vaccine hesitancy and low vaccine uptake.^14,15 Racial/ethnic disparities extended to the receipt of influenza vaccine recommendations, with Black and Asian pregnant women being less likely to be advised by their health care providers to get vaccinated compared with White women.¹³

Breastfeeding is a multifactorial health behavior that is associated with short-term and long-term benefits for mothers and their infants. Infant health benefits of longer duration of breastfeeding (at least 7 months) include reduced risk of respiratory infections and hospitalizations owing to any infection.^16,17 Using data from a longitudinal study in the United States with a sample of 1,281 six-year-old children who had been breastfed, those breastfed for at least 9 months had lower odds of ear and sinus infections compared with those breastfed <3 months.¹⁸

According to Healthy People 2020, 6-month overall breastfeeding rates should be at 60.6%, although the 2017 rate was 58.3%.¹⁹ Factors associated with early termination of breastfeeding in the United States by 8 weeks postpartum, include maternal sociodemographic factors of race/ethnicity, lack of private health insurance, lower level of educational attainment, maternal health factors, and lack of breastfeeding education and support while in the hospital.²⁰ Researchers also found that the maternal prenatal health behaviors of engaging in physical activity was associated with longer breastfeeding duration among a small sample of U.S. women,²¹ whereas prenatal smoking²² and use of electronic nicotine delivery system (ENDS) were associated with earlier breastfeeding cessation.²³

There is a dearth of population-based research on the association between the prenatal health behavior of influenza vaccination and breastfeeding duration in the United States.

Materials and Methods

This study utilized the 2016–2019 Pregnancy Risk Assessment and Monitoring System (PRAMS) data collected by the Centers for Disease Control and Prevention (CDC) in conjunction with state health departments.²⁴ A detailed description of the methods used to collect PRAMS data is available elsewhere.²⁵ In brief, PRAMS is a surveillance system that captures information on maternal experiences and behaviors during preconception, prenatal, and postpartum periods. PRAMS participants consisted of women who had a recent live birth selected randomly from state birth registries. Approximately 1,000–3,400 women are selected per year in each participating site.

To ensure availability of adequate data in smaller but higher-risk populations, samples are stratified by specific characteristics. Participants are initially contacted by mail or contacted and interviewed by telephone if there is no response to repeated mailings. Specific medical data including maternal diabetes and hypertension in pregnancy were drawn from birth certificate data and combined with the self-reported survey data. Fully de-identified data are available to researchers by the CDC. This study was deemed exempt by the researchers' Institutional Review Board because it was a secondary analysis of publicly available data.

A total of 164,404 mothers participated in PRAMS Phase 8. This study is restricted to PRAMS participants who had given birth to a singleton infant who was at least 13 weeks old and was alive at the time of the survey (n = 131,980). Participants who reported receipt of influenza vaccine before pregnancy (“yes, before pregnancy” response) (n = 15,032) and those with missing data on influenza vaccine (n = 3,197) and the covariates (n = 29,775) were excluded from the study. The final study sample consisted of 83,976 postpartum women.

The dependent variable for this study was breastfeeding for at least 3 months, defined as reported breastfeeding of any amount for at least 13 weeks. Because exclusivity of breastfeeding was not captured in PRAMS phase 8, the definition of breastfeeding duration includes any breastfeeding. To identify women for inclusion, women who responded “yes” to “Did you ever breastfeed or pump breast milk to feed your new baby, even for a short period of time?” were included in the analysis. The variable of “breastfeeding in weeks” as reported at the time of survey completion was used to define breastfeeding duration.

The main independent variable was receipt of influenza vaccine during pregnancy. A dichotomous variable was created using the two response options of “no” and “yes, during pregnancy” to the question, “During the 12 months before the delivery of your new baby, did you get a flu shot?” to indicate influenza vaccination status during pregnancy.

Based on a review of existing literature, the following covariates were selected: maternal sociodemographic factors of age (<20, 20–24, 25–34, >34), married (no, yes), race/ethnicity (non-Hispanic White, non-Hispanic Black, Hispanic, other), parity (primiparous, multiparous), education (<high school, high school, >high school), prenatal insurance (uninsured, Medicaid, private insurance, TRICARE or military insurance, state government plan, other), and receipt of Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) benefits during pregnancy (no, yes).

Infant factors of gestational age (<37 weeks preterm, ≥37 weeks full term), birth weight in grams (<2,500, 2,500–4,000, >4,000), sex of infant (male, female); prepregnancy and prenatal mothers health factors of mode of birth (vaginal, cesarean), prepregnancy body mass index (BMI) (underweight, normal weight, overweight, obese), gestational weight gain (below, within, above Institute of Medicine [IOM] guidelines), hypertension during pregnancy (no, yes), prepregnancy diabetes (no, yes), gestational diabetes mellitus (GDM) (no, yes), quality of prenatal care based on the Kotelchuck index (inadequate, intermediate, adequate, adequate plus), and receipt of recommendation of influenza vaccination during pregnancy (no, yes); and, maternal behaviors of prenatal cigarette smoking (no, yes) and prenatal ENDS use (no, yes).

Statistical analysis

Frequencies and percentages were used to describe the characteristics of the study sample. Rao–Scott chi-square tests were conducted to examine differences in the proportions of breastfeeding for at least 3 months by influenza vaccination status during pregnancy and other covariates. Multivariable logistic regression analysis was performed to examine the independent association between being vaccinated against influenza during pregnancy and breastfeeding for at least 3 months. Variables with p < 0.2 in the bivariate analysis were retained in the multivariable analysis. Unadjusted and adjusted odds ratios (ORs), 95% confidence intervals (CIs), and p-values were reported. p < 0.05 was considered statistically significant. Complex sample design elements of PRAMS were incorporated in all analyses. All analyses were performed using SAS 9.4 (SAS, Inc., Cary, NC).

Results

Overall, 68.3% (n = 57,269) of women breastfed for at least 3 months and 56.6% (n = 48,834) received the influenza vaccine during pregnancy. Characteristics of the women who participated in the study are given in Table 1. Women who did not receive the influenza vaccine during pregnancy were significantly less likely to breastfeed for at least 3 months compared with women who received the vaccine during pregnancy (64.5% versus 71.1%; p < 0.001).

Table 1.

Characteristics of the Study Sample (N = 83,976)

	n (wt.%)
Maternal sociodemographic factors
Age, years
<20	3,624 (3.8)
20–24	15,601 (18.4)
24–34	49,585 (59.5)
>34	15,166 (18.3)
Married
No	31,789 (35.2)
Yes	52,187 (64.8)
Race/ethnicity
Non-Hispanic white	40,962 (59.5)
Non-Hispanic black	14,033 (13.8)
Hispanic	14,963 (17.2)
Other	14,018 (9.5)
Parity
Primiparous	34,185 (40.2)
Multiparous	49,791 (59.8)
Education
<High school	8,191 (9.1)
High school	19,186 (23)
>High school	56,599 (67.8)
Prenatal insurance
Uninsured	10,052 (13.0)
Medicaid	22,087 (22.1)
Private	42,518 (53.8)
TRICARE or military	1,791 (2.2)
State government plan	1,590 (1.3)
Other	5,938 (7.5)
WIC recipient during pregnancy
No	53,609 (67.2)
Yes	30,367 (32.8)
Infant factors
Gestational age
Preterm	11,927 (7.2)
Full term	72,049 (92.8)
Birth weight (g)
<2,500	14,263 (5.8)
2,500–4,000	63,479 (85.5)
>4,000	6,234 (8.7)
Infant sex
Male	42,272 (51.2)
Female	41,704 (48.8)
Maternal health factors
Mode of birth
Vaginal	56,004 (68.5)
Cesarean	27,972 (31.5)
Prepregnancy BMI
Underweight	4,744 (5.3)
Normal	36,702 (45.0)
Overweight	21,115 (25.5)
Obese	21,415 (24.2)
Gestational weight gain
Below IOM guidelines	21,981 (23.6)
Within IOM guidelines	25,628 (30.7)
Above IOM guidelines	36,367 (45.7)
Hypertension during pregnancy
No	75,109 (91.4)
Yes	8,867 (8.6)
Prepregnancy diabetes
No	81,429 (97.0)
Yes	2,547 (3.0)
Gestational diabetes
No	78,079 (93.5)
Yes	5,897 (6.5)
Kotelchuck index
Inadequate	9,376 (11.1)
Intermediate	8,602 (10.3)
Adequate	37,125 (46.4)
Adequate plus	28,873 (32.1)
Received recommendation of influenza vaccine from HCP
No	10,972 (13.5)
Yes	73,004 (86.5)
Maternal behaviors
Prenatal cigarette smoking
No	78,065 (93.7)
Yes	5,911 (6.3)
Prenatal ENDS use
No	83,072 (99.0)
Yes	904 (1.0)
Received influenza vaccine during pregnancy
No	35,142 (43.4)
Yes	48,834 (56.6)
Breastfeeding duration
<3 months	26,707 (31.7)
≥3 months	57,269 (68.3)

BMI, body mass index; ENDS, electronic nicotine delivery systems; HCP, health care provider; IOM, Institute of Medicine; WIC, Special Supplemental Nutrition Program for Women, Infants, and Children; wt.%, weighted percent.

Significant covariates associated with ≥3-month breastfeeding duration included maternal sociodemographic factors (older age, being married, multiparous, higher level of education, race/ethnicity, not being a WIC recipient, private or military health insurance), infant factors (term gestation and birthweight ≥2,500 g), maternal health factors (vaginal birth, adequate prenatal care, not having prepregnancy obesity, gestational weight gain within IOM guidelines, not having hypertension or GDM, and received recommendation to get the influenza vaccine during pregnancy), and prenatal health behaviors (not smoking cigarettes or ENDS during pregnancy) (Table 2).

Table 2.

Characteristics of the Study Sample by Breastfeeding Duration (N = 83,976)

	<3 months, n (wt. %)	≥3 months, n (wt. %)	p
Maternal sociodemographic factors
Age, years			<0.001
<20	2,120 (60.1)	1,504 (39.9)
20–24	7,001 (45.5)	8,600 (54.5)
24–34	13,808 (28.0)	35,777 (72.0)
>34	3,778 (24.1)	11,388 (75.9)
Married			<0.001
No	15,055 (48.5)	16,734 (51.5)
Yes	11,652 (22.6)	40,535 (77.4)
Race/ethnicity			<0.001
Non-Hispanic white	11,432 (28.7)	29,530 (71.3)
Non-Hispanic black	6,024 (44.2)	8,009 (55.8)
Hispanic	5,411 (36.0)	9,552 (64.0)
Other	3,840 (25.2)	10,178 (74.8)
Parity			<0.001
Primiparous	11,722 (34.7)	22,463 (65.3)
Multiparous	14,985 (29.7)	34,806 (70.3)
Education			<0.001
<High school	3,890 (45.5)	4,301 (54.5)
High school	8,680 (45.7)	10,506 (54.3)
>High school	14,137 (25.1)	42,462 (74.9)
Prenatal insurance			<0.001
Uninsured	3,720 (37.3)	6,332 (62.7)
Medicaid	10,068 (46.1)	12,019 (53.9)
Private	9,632 (23.4)	32,886 (76.6)
TRICARE or military	384 (20.5)	1,407 (79.5)
State government plan	673 (44.7)	917 (55.3)
Other	2,230 (40.1)	3,708 (59.9)
WIC recipient during pregnancy			<0.001
No	13,162 (25.0)	40,447 (75.0)
Yes	13,545 (45.6)	16,822 (54.4)
Infant factors
Gestational age			<0.001
Preterm	4,976 (43.1)	6,951 (56.9)
Full term	21,731 (30.9)	50,318 (69.1)
Birth weight (g)			<0.001
<2,500	5,908 (44.4)	8,355 (55.6)
2,500–4,000	19,176 (31.3)	44,303 (68.7)
>4,000	1,623 (27.3)	4,611 (72.7)
Infant sex			0.754
Male	13,489 (31.7)	28,783 (68.3)
Female	13,218 (31.8)	28,486 (68.2)
Maternal health factors
Mode of birth			<0.001
Vaginal	16,769 (30.1)	39,235 (69.9)
Cesarean	9,938 (35.4)	18,034 (64.6)
Prepregnancy BMI			<0.001
Underweight	1,332 (27.5)	3,412 (72.5)
Normal	9,798 (26.3)	26,904 (73.7)
Overweight	6,736 (32.4)	14,379 (67.6)
Obese	8,841 (42.0)	12,574 (58.0)
Gestational weight gain			<0.001
Below IOM guidelines	7,455 (33.0)	14,526 (67.0)
Within IOM guidelines	7,309 (28.3)	18,319 (71.7)
Above IOM guidelines	11,943 (33.4)	24,424 (66.6)
Hypertension during pregnancy			<0.001
No	23,123 (30.9)	51,986 (69.1)
Yes	3,584 (41.0)	5,283 (59.0)
Prepregnancy diabetes			0.001
No	25,720 (31.6)	55,709 (68.4)
Yes	987 (36.5)	1,560 (63.5)
Gestational diabetes			0.001
No	24,741 (31.5)	53,338 (68.5)
Yes	1,966 (34.8)	3,931 (65.2)
Kotelchuck index			<0.001
Inadequate	3,589 (37.4)	5,787 (62.6)
Intermediate	2,688 (30.8)	5,914 (69.2)
Adequate	10,557 (29.1)	26,568 (70.9)
Adequate plus	9,873 (33.9)	19,000 (66.1)
Received recommendation of influenza vaccine from HCP			<0.001
No	4,090 (36.8)	6,882 (63.2)
Yes	22,617 (30.9)	50,387 (69.1)
Maternal behaviors
Prenatal cigarette smoking			<0.001
No	23,174 (29.8)	54,891 (70.2)
Yes	3,533 (60.0)	2,378 (40.0)
Prenatal ENDS use			<0.001
No	26,207 (31.5)	56,865 (68.5)
Yes	500 (55.6)	404 (44.4)
Received influenza vaccine during pregnancy			<0.001
No	12,497 (35.5)	22,645 (64.5)
Yes	14,210 (28.9)	34,624 (71.1)

Rao–Scott chi-square p-values.

Results of the unadjusted and adjusted logistic regression analyses are given in Table 3. In the multivariable model, the odds of breastfeeding at least 3 months were significantly lower in women who did not receive the influenza vaccine during pregnancy compared with those who were vaccinated (OR, 0.92; 95% CI, 0.88–0.98; p = 0.005).

Table 3.

Association Between Receipt of Influenza Vaccination During Pregnancy and Breastfeeding for ≥3 Months (N = 83,976)

	Crude OR (95% CI)	p	Adjusted OR (95% CI)	p
Maternal sociodemographic factors
Age, years
<20	0.21 (0.19–0.24)	<0.001	0.50 (0.43–0.58)	<0.001
20–24	0.38 (0.35–0.41)	<0.001	0.65 (0.60–0.72)	<0.001
24–34	0.81 (0.76–0.87)	<0.001	0.91 (0.84–0.97)	0.005
>34	Reference		Reference
Married
No	0.31 (0.30–0.33)	<0.001	0.54 (0.51–0.58)	<0.001
Yes	Reference		Reference
Race/ethnicity
Non-Hispanic white	Reference		Reference
Non-Hispanic black	0.51 (0.47–0.54)	<0.001	0.87 (0.81–0.95)	0.001
Hispanic	0.71 (0.67–0.76)	<0.001	1.04 (0.96–1.12)	0.370
Other	1.19 (1.10–1.29)	<0.001	1.19 (1.10–1.30)	<0.001
Parity
Primiparous	0.80 (0.76–0.84)	<0.001	0.83 (0.78–0.88)	<0.001
Multiparous	Reference		Reference
Education
<High school	0.40 (0.37–0.44)	<0.001	0.72 (0.66–0.79)	<0.001
High school	0.40 (0.38–0.42)	<0.001	0.68 (0.64–0.73)	<0.001
>High school	Reference		Reference
Prenatal insurance
Uninsured	0.51 (0.48–0.56)	<0.001	1.04 (0.95–1.14)	0.374
Medicaid	0.36 (0.34–0.38)	<0.001	0.86 (0.79–0.93)	<0.001
Private	Reference		Reference
TRICARE or military	1.19 (0.98–1.44)	0.076	1.29 (1.06–1.56)	0.012
State government plan	0.38 (0.31–0.46)	<0.001	0.83 (0.68–1.02)	0.078
Other	0.46 (0.42–0.50)	<0.001	0.97 (0.88–1.08)	0.607
WIC recipient during pregnancy
No	Reference		Reference
Yes	0.40 (0.38–0.42)	<0.001	0.75 (0.70–0.79)	<0.001
Infant factors
Gestational age
Preterm	0.59 (0.55–0.63)	<0.001	0.79 (0.71–0.87)	<0.001
Full term	Reference		Reference
Birth weight (g)
<2,500	0.57 (0.54–0.61)	<0.001	0.88 (0.80–0.97)	0.008
2,500–4,000	Reference		Reference
>4,000	1.22 (1.12–1.33)	<0.001	1.11 (1.01–1.22)	0.034
Maternal health factors
Mode of birth
Vaginal	Reference		Reference
Cesarean	0.79 (0.75–0.82)	<0.001	0.80 (0.76–0.85)	<0.001
Prepregnancy BMI
Underweight	1.26 (1.12–1.42)	<0.001	1.34 (1.18–1.52)	<0.001
Normal	Reference		Reference
Overweight	1.34 (1.26–1.42)	<0.001	1.27 (1.19–1.36)	<0.001
Obese	0.66 (0.62–0.70)	<0.001	0.75 (0.70–0.81)	<0.001
Gestational weight gain
Below IOM guidelines	0.80 (0.75–0.85)	<0.001	0.95 (0.88–1.02)	0.124
Within IOM guidelines	Reference		Reference
Above IOM guidelines	0.79 (0.74–0.83)	<0.001	0.95 (0.89–1.00)	0.068
Hypertension during pregnancy
No	Reference		Reference
Yes	0.64 (0.60–0.69)	<0.001	0.83 (0.76–0.90)	<0.001
Prepregnancy diabetes
No	Reference	0.001	Reference
Yes	0.80 (0.71–0.92)		0.87 (0.75–1.01)	0.076
Gestational diabetes
No	Reference		Reference
Yes	0.86 (0.79–0.95)	0.001	0.85 (0.77–0.93)	0.004
Kotelchuck index
Inadequate	0.86 (0.79–0.93)	<0.001	1.07 (0.98–1.17)	0.156
Intermediate	1.16 (1.06–1.26)	0.001	1.1 (1.01–1.21)	0.036
Adequate	1.25 (1.19–1.32)	<0.001	1.08 (1.02–1.15)	0.007
Adequate plus	Reference		Reference
Received recommendation of influenza vaccine from HCP
No	0.77 (0.72–0.82)		0.96 (0.89–1.04)	0.293
Yes	Reference		Reference
Maternal behaviors
Prenatal cigarette smoking
No	Reference		Reference
Yes	0.28 (0.26–0.31)	<0.001	0.44 (0.40–0.49)	<0.001
Prenatal ENDS use
No	Reference		Reference
Yes	0.37 (0.30–0.46)	<0.001	0.78 (0.60–1.02)	0.065
Received influenza vaccine during pregnancy
No	0.74 (0.70–0.77)	<0.001	0.92 (0.88–0.98)	0.005
Yes	Reference		Reference

BMI, body mass index; CI, confidence interval; ENDS, electronic nicotine delivery systems; HCP, health care provider; IOM, Institute of Medicine; OR, odds ratio; WIC, Special Supplemental Nutrition Program for Women, Infants, and Children.

Discussion

The main finding of the study indicates that receipt of influenza vaccination during pregnancy is significantly associated with longer duration of breastfeeding (at least 3 months) in a large, population-based sample of mothers. To our knowledge, this is the first published study to find a positive association between the health behavior of prenatal influenza vaccination and breastfeeding duration in the United States.

Prenatal vaccination and breastfeeding are both health promotional, along with other pregnancy behaviors such as avoidance of alcohol and smoking, engaging in physical activity, and intake of vitamin and mineral supplementation during pregnancy. A qualitative study in a U.S. sample of women found a connection between the health promotional prenatal behavior of physical activity and breastfeeding duration.²¹ Previous research also found that the prepregnancy health behavior of folic acid intake is a predictor of breastfeeding duration.²⁶ Using older PRAMS data, other maternal behaviors negatively associated with breastfeeding duration were alcohol consumption,²⁰ prenatal smoking, and ENDS use,²³ supporting our findings.

Additional significant factors positively associated with ≥3-month breastfeeding duration in the multivariable model were maternal sociodemographic characteristics including older age, higher level of education, being married, multiparity, and other race/ethnicity; perinatal health factors significantly associated were adequate prenatal care, vaginal birth, and giving birth at term gestation. Negatively associated with breastfeeding duration were maternal sociodemographic characteristics of Medicaid insurance and receiving WIC benefits, maternal health factors of having prepregnancy obesity, hypertension, and GDM, and infant factors of preterm and low birthweight. These factors are supported by previous research studies and reports in the United States.

According to the CDC, the lowest breastfeeding 6-month duration rates in 2017 were among mothers who were unmarried, non-Hispanic Black, younger age, lower educated, poorer, WIC recipients, and lived in nonmetropolitan areas.²⁷ A 2010–2011 cohort study in the western region of the United States found longer duration of breastfeeding was significantly associated with higher maternal education, absence of prepregnancy medical conditions, giving birth at term gestation, and the prenatal behavior of folic acid intake.²⁶

Using PRAMS data from 2012 to 2013, researchers also found maternal sociodemographic, health, and behavioral factors, as well as formula use and breastfeeding-related practices in the hospital to be associated with breastfeeding duration, although the maternal sociodemographic factors were not consistently significant across specific time points in the first 2 months.²⁰

As in our study findings, race/ethnicity has been noted to be a significant factor in breastfeeding outcomes. Breastfeeding-related practices in the hospital significantly influenced breastfeeding duration among women of difference racial/ethnic backgrounds who gave birth in New Mexico in 2012–2014.²⁸ Results from the National Immunization Survey—Child of 167,842 infants born between 2009 and 2015, found increasing trends of continued breastfeeding through 12 months of age and 6-month exclusive breastfeeding duration with noted disparities based on race/ethnicity.²⁹ When promoting breastfeeding duration, it is recommended to consider maternal–infant sociodemographic, health, and prenatal behavioral characteristics including influenza vaccination to promote healthful decisions that are likely to reduce risks and complications.

Regarding prenatal influenza vaccination, consistent with our findings, a recent study identified significant predictors such as older maternal age, higher maternal education, race/ethnicity, not smoking in pregnancy, and having normal prepregnancy BMI.³⁰ Maternal influenza vaccination during pregnancy has a positive effect on sIgA levels in breast milk, whereas breastfeeding after maternal vaccination results in a lower incidence of influenza in young infants.^7,8,31 This finding complements research demonstrating the positive influence of prenatal vaccination on antibody levels in breast milk against other infectious diseases such as meningococcus and pneumococcus.³¹

Among 500 women who were pregnant during the 2016–2017 influenza season, 66% (n = 330) reported being vaccinated, with significant predictors including primiparity, higher education, and routine annual vaccination. The researchers also found that among women who were vaccinated, primary reasons to get vaccinated included the belief that the vaccine protected the pregnant woman and her infant from infection and health care provider recommendations to vaccinate.³² Yet, pregnant and breastfeeding women have expressed concern about the safety of the vaccine, side effects, and harm to their infants,^33,34 possibly related to negative messages and misinformation propagated through social media.³⁵

Research has established the safety of vaccination during pregnancy⁶ and shown no association between prenatal influenza vaccination and adverse prenatal or neonatal outcomes.^8,30 Both active and inactive vaccines were found to be safe in vaccinated pregnant women regardless of timing of vaccination. Furthermore, prenatal influenza vaccination reduced the risks of influenza, maternal fever, preeclampsia, placental abruption, stillbirth, and neonatal intensive care unit admission.³⁰

Despite the benefits of influenza vaccination on maternal and infant health, the recent nationally representative rate of vaccination uptake among pregnant women is suboptimal at 56.4%, although it is higher than previously reported in 2012–2016.¹⁰ These rates are lower than the 2018–2019 internet panel survey rate, which may be explained by possible selection bias, differences in timing, region, culture, and sociodemographic characteristics of participants, and state-specific health policies and initiatives.^11,30,36 Vaccine policy strategies and guidelines are updated annually³⁷ and should be communicated to patients. It is therefore critical for health care providers to educate pregnant women about the importance of influenza vaccination, explaining the safety and health protection for their infants, thereby dispelling incorrect information.³⁸

Limitations of the study are the cross-sectional design that does not account for causal effect and the self-reported data collection of most of the variables increasing the risk of reporting bias. The data did not contain information on in-hospital formula feeding or 3-month exclusive breastfeeding, national indicators of breastfeeding outcomes, and negative predictors of breastfeeding duration. In addition, the PRAMS core survey does not inquire into fertility treatment, although research is suggested that the use of fertility treatment is associated with shorter breastfeeding duration.³⁹ The strengths of the study include the collection of specific variables from objectively reported birth certificates and the large, heterogenic, and representative sample of U.S. mothers who recently participated in the PRAMS survey, increasing the generalizability of the study findings.

Conclusions

Findings from the secondary data analysis indicate an association between the health-promotional behaviors of prenatal influenza vaccination and breastfeeding duration in a nationally representative U.S. sample. Vaccinated pregnant women were more likely to breastfeed for at least 3 months compared with those not vaccinated during pregnancy. This association suggests a link between health promotional behaviors among pregnant and postpartum women. Population level interventions should be developed to reduce disparities including health behaviors and outcomes among pregnant women. Recommendations and education by health care providers should include a focus on maternal health behaviors to support positive maternal–infant health outcomes including reduced infection and extended breastfeeding duration.

Footnotes

Authors' Contributions

R.A.M. contributed to the idea development, data analysis, interpretation of the results, and writing of the article; Z.T.H. contributed to the idea development, data analysis, interpretation of the results, and writing of the article; and I.R.A.C. contributed to the idea development, data analysis, interpretation of the results, and writing of the article. All authors reviewed and confirmed the final version of the article.

Acknowledgments

The authors acknowledge the PRAMS Working Group (Alabama: Izza Afgan, MPH; Alaska: Kathy Perham Hester, MS, MPH; Arkansas: Mary McGehee, PhD; Colorado: Rickey Tolliver, MPHC; Connecticut: Jennifer Morin, MPH; Delaware: George Yocher, MS; Florida: Elizabeth C. Stewart, MSPH; Georgia: Florence A. Kanu, MPH; Hawaii: Matt Shim, PhD, MPH; Illinois: Patricia Kloppenburg, MT [ASCP], MPH; Iowa: Jessica Egan; Kentucky: Tracey D. Jewell, MPH; Louisiana: Rosaria Trichilo, MPH; Maine: Tom Patenaude, MPH; Maryland: Laurie Kettinger, MS; Massachusetts: Emily Lu, MPH; Michigan: Peterson Haak; Minnesota: Mira Grice Sheff, PhD, MS; Mississippi: Brenda Hughes, MPPA; Missouri: David McBride, PhD; Montana: Emily Healy, MS; Nebraska: Jessica Seberger; New Hampshire: David J. Laflamme, PhD, MPH; New Jersey: Sharon Smith Cooley, MPH; New Mexico: Oralia Flores; New York State: Anne Radigan; New York City: Pricila Mullachery, MPH; North Carolina: Kathleen Jones Vessey, MS; North Dakota; Grace Njau, MPH; Ohio: Connie Geidenberger, PhD; Oklahoma: Ayesha Lampkins, MPH, CHES; Oregon: Claudia W. Bingham, MPH; Pennsylvania: Tony Norwood; Rhode Island: Karine Tolentino Monteiro, MPH; South Carolina: Kristin Simpson, MSW, MPA; Texas: Tanya Guthrie, PhD; Tennessee: Ramona Lainhart, PhD; Utah: Nicole Stone; Vermont: Peggy Brozicevic; Virginia: Sara Varner, MPH; Washington: Linda Lohdefinck; West Virginia: Melissa Baker, MA; Wisconsin: Christopher Huard; and Wyoming: Lorie Chesnut, PhD); and CDC PRAMS Team, Applied Sciences Branch, Division of Reproductive Health.

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

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