Seasonal Influenza and 2009 H1N1 Influenza Vaccination Coverage Among Pregnant Women --- 10 States, 2009--10 Influenza Season

Because pregnant women are at increased risk for severe disease associated with influenza infection, the American College of Obstetricians and Gynecologists and the Advisory Committee on Immunization Practices have recommended seasonal influenza vaccination for women while pregnant, regardless of trimester (1,2). In 2009, a novel strain of influenza A (H1N1) virus was identified (3), and pregnant women also were found to be at greater risk for influenza-related complications from this new virus (4). As a result, during the 2009--10 influenza season, two separate influenza vaccines were recommended to pregnant women: inactivated trivalent 2009--10 seasonal vaccine and influenza A (H1N1) 2009 monovalent vaccine (2,5). To estimate influenza vaccination coverage among pregnant women during the 2009--10 influenza season, CDC analyzed data from 10 states from the Pregnancy Risk Assessment Monitoring System (PRAMS). This report summarizes the results of that analysis, which determined that vaccination coverage for pregnant women among the 10 states combined was 50.7% for seasonal influenza and 46.6% for 2009 H1N1. In addition, women to whom vaccination was offered or recommended by their health-care provider were significantly more likely to report being vaccinated against seasonal influenza (relative risk [RR] = 3.3) and 2009 H1N1 (RR = 10.1). These results indicate substantially higher influenza vaccination coverage among pregnant women than has been reported for previous influenza seasons (2,5,6) and support previous findings that receipt of influenza vaccination can be influenced greatly by health-care providers offering or recommending influenza vaccination (6,7).

CDC analyzed data from PRAMS, an ongoing, population-based surveillance system that collects information on a wide range of maternal behaviors and experiences before, during, and after pregnancy. PRAMS surveys currently are administered by 37 states and New York City. The surveys consist of monthly stratified random samples of 100--300 women with recent live births recorded in state birth certificate registries. Selected mothers are mailed a questionnaire 2--6 months after delivery, and those who do not respond by mail are contacted by telephone.*

To assess seasonal and 2009 H1N1 influenza vaccination coverage among pregnant women, supplemental questions were added to the PRAMS survey. During the 2009--10 influenza season, 30 states agreed to participate in the supplemental influenza assessment. For this analysis, 10 states† were selected that submitted their data to CDC by September 15 and had a response rate ≥65%. Included in this analysis were 6,225 women with non-missing data regarding seasonal influenza vaccination who had live births during September 1, 2009--March 12, 2010, and 5,112 women with non-missing data regarding 2009 H1N1 vaccination who had live births during October 1, 2009--March 12, 2010. In addition, to compare seasonal and 2009 H1N1 vaccination coverage within the same sample of women, data for the 5,052 women with complete data for both vaccinations who had live births during October 1, 2009--March 12, 2010, were analyzed. The 2009 H1N1 vaccination became available on October 5, 2009.

PRAMS data were analyzed to estimate seasonal and 2009 H1N1 influenza vaccination coverage; 95% confidence intervals (CIs) and Wald chi-square tests were used to assess statistically significant associations. In the seasonal influenza sample, participants were asked, "Since September 2009, did you get a seasonal flu shot?" and "At any time during your most recent pregnancy, did a doctor, nurse, or other health-care worker offer you a seasonal flu shot or tell you to get one?" Participants also were asked, "During your most recent pregnancy, did you get an H1N1 flu shot?" and "At any time during your most recent pregnancy, did a doctor, nurse, or other health-care worker offer you an H1N1 flu shot or tell you to get one?" Participants who did not receive seasonal or 2009 H1N1 vaccinations were asked to select any reasons that applied to them from a list of reasons for not receiving the vaccinations. The data were weighted to adjust for complex survey design and nonresponse. Nearly all (98.9%) PRAMS respondents who received the influenza supplement on the questionnaire also responded to the influenza questions.

Combining the data from all 10 states included in this analysis, 50.7% (state median: 50.7%; range: 36.6%--68.3%) of the 6,225 women in the seasonal influenza sample reported receiving the seasonal influenza vaccination since September 2009, and 46.6% (state median: 45.5%; range: 26.9%--72.4%) of the 5,112 women in the 2009 H1N1 sample reported receiving the 2009 H1N1 influenza vaccination while pregnant (Table). To compare seasonal and 2009 H1N1 vaccination coverage within the same sample, data for the 5,052 women with live births during October 1, 2009--March 12, 2010, and complete influenza vaccination data were analyzed; 66.0% received at least one of the vaccinations, and 34.0% received neither. Among the 5,052 women, 34.1% received both influenza vaccinations during their pregnancy, 19.7% received only the seasonal vaccination, and 12.2% received only the 2009 H1N1 vaccination (Table).

Large percentages of women reported that their health-care provider had offered or recommended the seasonal influenza vaccination (67.4%) and 2009 H1N1 vaccination (75.2%). Among those whose health-care provider offered or recommended the seasonal vaccination, larger proportions reported receiving the vaccination than among those whose health-care provider did not offer or recommend it (65.8% versus 19.6%) (RR = 3.3; CI = 2.9--3.9). Among those whose health-care provider offered or recommended the 2009 H1N1 vaccination, larger proportions reported receiving the vaccination than among those whose health-care provider did not offer or recommend it (60.1% versus 5.9%) (RR = 10.1; CI = 7.7--14.3).

Among 2,290 women who received the 2009 H1N1 vaccination, 50.9% reported receiving it at the office of their obstetrician/gynecologist, and 25.7% received it at a health department or community clinic (Table). Among 2,994 who did not receive the seasonal influenza vaccination, 47.7% cited safety concerns for their baby, and 45.2% cited safety concerns for themselves. Among 2,602 who did not receive the 2009 H1N1 vaccination, 63.6% cited safety concerns for their baby, and 61.4% cited safety concerns for themselves (Table).

Reported by

IB Ahluwalia, PhD, DJ Jamieson, MD, DV D'Angelo, MPH; Div of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion; JA Singleton, MS, T Santibanez, PhD, G Euler, DrPH, C Weinbaum, MD, Immunization Svcs Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note

Historically, seasonal influenza vaccination coverage among pregnant women has been low; during the 2007--08 influenza season, coverage was 24.2%, and during the 2008--09 season, it was 11.3%, according to the National Health Interview Survey (2). Vaccination of pregnant women with the seasonal influenza and monovalent 2009 H1N1 influenza vaccines was a focus of public health efforts during the 2009--10 influenza season (1,2,4,5), and the PRAMS data from 10 states in this report show higher vaccination coverage among pregnant women for both seasonal and 2009 H1N1 influenza vaccination. Estimated coverage for pregnant women in these states also was higher than estimates from a different survey for persons aged ≥18 years from the same 10 states; that survey found state median seasonal influenza vaccination coverage of 39.7% (range: 36.0%--48.5%) and 2009 H1N1 vaccination coverage of 21.4% (range: 8.7%--27.8%) (8,9).

The greater vaccination coverage for those who were offered vaccination or received a recommendation for vaccination from their health-care provider reinforces previous findings that doctor's recommendations for vaccination are key in vaccination acceptance (6). With a novel virus, 2009 H1N1, the role of health-care providers in reassuring pregnant women might have been critical because of patient concerns regarding the new vaccine. Although 46.6% of those sampled received the 2009 H1N1 vaccination, large percentages of those who were not vaccinated cited concerns over the safety of the vaccine for their babies and themselves, similar to previous studies (6,7,10).

During the 2009--10 influenza season, in addition to educational efforts aimed at providers and the general population, certain other factors might have contributed to the increase in influenza vaccination coverage among pregnant women. These include the designation of pregnant women as a high-priority group to receive the influenza vaccinations, extensive multisectoral (i.e., public and private entities) collaboration to implement the 2009 H1N1 vaccination campaign, media attention to the 2009 H1N1 pandemic, and provision of monovalent 2009 H1N1 vaccine at no cost to vaccination providers.

The findings in this report are subject to at least three limitations. First, these PRAMS data were only available from 10 states and are not generalizable to all pregnant women in the United States. Second, influenza vaccination status and information on provider recommendations were reported by the mother and not verified by medical record, and might be subject to recall bias. Finally, the cohort of women available for this analysis (September 1, 2009--March 12, 2010) represents a subset of all women who were pregnant during the periods when seasonal and 2009 H1N1 vaccines were available during the 2009--10 influenza season. Most of these women were in their second or third trimester of pregnancy during the vaccination period, and those delivering early in the vaccination period would have had less opportunity for vaccination. To estimate vaccination coverage for the entire influenza season, data from women giving birth throughout the influenza season would be needed.

Based on the findings in this report, influenza vaccination coverage among pregnant women was higher during the 2009--10 season than has been described in past influenza seasons. Approximately 4 million births occur annually in the United States, and a large proportion of women likely are pregnant during the usual influenza vaccination period. Continued education of both health-care providers and pregnant women is needed regarding the risk for influenza complications during pregnancy and the safety and protective effect of vaccinations for both mother and child (10).

Acknowledgments

The findings in this report are based, in part, on contributions by the PRAMS influenza working group, including T Austin, MPA, P Hastings, PhD, N Ruffo, MPA, and ME O'Neil, MPH.

References

1. American College of Obstetricians and Gynecologists Committee on Obstetric Practice. ACOG committee opinion number 305, November 2004. Influenza vaccination and treatment during pregnancy. Obstet Gynecol 2004;104(5 pt 1):1125--6.
2. CDC. Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2010. MMWR 2010;59(No. RR-8).
3. Novel Swine-Origin Influenza A (H1N1) Virus Investigation Team. Emergence of a novel swine-origin influenza A (H1N1) virus in humans. N Engl J Med 2009;360:2605--15.
4. Jamieson DJ, Honein MA, Rasmussen SA, et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet 2009;374:451--8.
5. CDC. Use of influenza A (H1N1) 2009 monovalent vaccine: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009. MMWR 2009;58(No. RR-10).
6. Ahluwalia IB, Jamieson DJ, Rasmussen SA, D'Angelo D, Goodman D, Kim H. Correlates of seasonal influenza vaccine among pregnant women in Georgia and Rhode Island. Obstet Gynecol 2010;116:949--55.
7. Broughton DE, Beigi RH, Switzer GE, Raker CA, Anderson BL. Obstetric health care worker's attitudes and beliefs regarding influenza vaccination in pregnancy. Obstet Gynecol 2009;114:981--7.
8. CDC. Interim results: state-specific seasonal influenza vaccination coverage---United States, August 2009--January 2010. MMWR 2010;59:477--84.
9. CDC. Interim results: state-specific influenza A (H1N1) 2009 monovalent vaccination coverage---United States, October 2009--January 2010. MMWR 2010;59:363--8.
10. Zaman K, Roy E, Arifeen SE, et al. Effectiveness of maternal influenza immunization in mothers and infants. N Engl J Med 2008;359:1555--64.

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