Review
Safety of influenza vaccination during pregnancy

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The Centers for Disease Control and Prevention Advisory Committee on Immunization Practices recommends routine influenza vaccination for all women who are or will be pregnant during the influenza season. During seasonal influenza epidemics, during previous pandemics, and with the current influenza A (H1N1) pandemic, pregnancy places otherwise healthy women at increased risk for serious complications from influenza, including death. Inactivated influenza vaccine can be safely and effectively administered during any trimester of pregnancy. No study to date has demonstrated an increased risk of either maternal complications or adverse fetal outcomes associated with inactivated influenza vaccination. Moreover, no scientific evidence exists that thimerosal-containing vaccines are a cause of adverse events among children born to women who received influenza vaccine during pregnancy. In this article, we review the evidentiary basis for the recommendation of vaccination of all women who will be pregnant during the influenza season and safety data of influenza vaccination during pregnancy.

Section snippets

Evolution of US immunization recommendations

The serious consequences of influenza infection during pregnancy have been recognized for almost a century. In a series of 1350 pregnant women reported during the 1918 pandemic, about 50% developed pneumonia, and of these women, more than half died, with a case fatality rate of 27%. 2, 12 The highest mortality was seen in the third trimester. During the pandemic of 1957, nearly half of all women of childbearing age who died were pregnant. 3, 13, 14, 15

Over the years, as data regarding the

Risks of influenza infection in pregnancy

Pregnancy is associated with biochemical, mechanical, hemodynamic, as well as immunologic changes in the mother that become most pronounced by the third trimester. These changes include decreased lung capacity and tidal volume, along with increased cardiac output and oxygen consumption. 19, 20, 21 Adaptive humoral immunity remains generally intact with augmentation of the T-helper-type 2 antibody-mediated response. 22 This is in contrast to the selective suppression of T-helper-type 1

Safety of inactivated influenza vaccine for the pregnant woman

The lack of harmful effects of inactivated influenza vaccination on maternal health during pregnancy has been demonstrated in several studies (Table30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41). Munoz et al32 performed a retrospective analysis of data from 5 influenza seasons using an electronic database of a large multispecialty clinic in the United States. Outcomes of pregnancy were compared between a cohort of 225 healthy women who received influenza vaccine during the second and third

Benefits of influenza vaccination for the neonate

Studies from the United States and Hong Kong demonstrate high rates of hospitalization among infants with influenza, especially in the age group <6 months.45, 46, 47 A review of the US influenza mortality during the 2003-2004 influenza season revealed that childhood deaths associated with influenza were most frequent in infants aged <6 months. 48 Because of limited immunogenicity in this age group, inactivated influenza vaccine is not currently licensed for infants <6 months of age.1

Safety of maternal influenza vaccination for the fetus

Many pregnant women struggle with the concept of vaccination during pregnancy because of theoretical concerns regarding harm to the fetus. In the longitudinal, population-based Collaborative Perinatal Project that was conducted between 1959-1965, >2000 pregnant women received influenza vaccination, almost a third during the first trimester. The children of these women were followed up for the first 7 years of life, and maternal influenza immunization did not increase the number of stillbirths,

Influenza vaccination and thimerosal

Thimerosal, a mercury-containing compound, is a preservative that has been used in some vaccines, including multivial inactivated influenza vaccines, to reduce the likelihood of microbial growth. Concerns came to public attention in 1999 because of uncertainty regarding the applicability of guidelines for long-term exposure to methylmercury, primarily from fish consumption, to intermittent exposure to ethylmercury, a breakdown product of thimerosal. Subsequent studies have shown that

Conclusion

Inactivated influenza vaccine can be safely and effectively administered during any trimester of pregnancy. No study to date has demonstrated an increased risk of either maternal complications or untoward fetal outcomes associated with inactivated influenza vaccination. In addition, no scientific evidence exists that thimerosal-containing vaccines are a cause of adverse events among children born to women who received influenza vaccine during pregnancy. Immunization of the mother reduces 1

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    Dr Tamma is supported by a National Institutes of Health (NIH) fellowship training Grant. Dr del Rio is supported by Grants from NIH (HIV vaccine trials network and vaccine treatment and evaluation units), Centers for Disease Control and Prevention (CDC), Emory Global Health Institute, Merck and Co., Inc. (West Point, PA), and Sanofi Pasteur. Dr Steinhoff is supported by the Bill and Melinda Gates Foundation, NIH, and Wyeth Vaccines. Dr Halsey is supported by Berna, Intercel, Merck (North Wales, PA), Novartis, CDC, and NIH. Dr Omer is supported by the Bill and Melinda Gates Foundation, CDC, Merck (North Wales, PA), and Emory Global Health Institute.

    Dr Omer was awarded the Maurice R. Hilleman Early-stage Career Investigator Award by the National Foundation for Infectious Diseases, funded by an unrestricted educational Grant to the National Foundation for Infectious Diseases from Merck and Co., Inc. However, Dr Omer had no direct interaction with Merck and Co., Inc. related to this award.

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