American Journal of Epidemiology Advance Access originally published online on December 7, 2006
American Journal of Epidemiology 2007 165(3):352-353; doi:10.1093/aje/kwk104
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LETTERS TO THE EDITOR |
TWO OF THE AUTHORS REPLY
Center for Health Research, Kaiser Permanente Northwest, Portland, OR 97227
(e-mail: allison.naleway{at}kpchr.org)
We thank Drs. Ayoub and Yazbak (1) for their comments on our article (2). Our recent review of the literature on influenza vaccination during pregnancy referenced several studies that describe influenza-related morbidity and mortality in pregnant women (2). Despite examining different populations over a wide range of influenza seasons and using differing study designs and outcome measures, when considered as a whole, these studies indicate that pregnant women have an increased risk of influenza and influenza-related complications relative to nonpregnant women. This increased risk is especially pronounced in the second and third trimesters, and in pregnant women with underlying medical conditions such as asthma. Although the rates of influenza-related hospitalizations cited in these studies are generally low, they are similar to hospitalization rates in other high-risk groups for which annual influenza vaccination is recommended by the Advisory Committee on Immunization Practices (ACIP) (3).
Influenza vaccine has been administered to pregnant women in the United States since the 1950s. While treatment technology has improved since that time, the goal of vaccinating pregnant women remains preventing influenza infection and its related complications, such as pneumonia and pulmonary edema. In the 1990s, the ACIP determined that these benefits warranted a recommendation for inactivated influenza vaccination during the second and third trimesters for healthy pregnant women, and at any time for pregnant women with certain chronic, underlying medical conditions. In 2004, the committee expanded its recommendation to include all pregnant women regardless of trimester (3).
We acknowledge that the few published studies of vaccine effectiveness during pregnancy have reported conflicting results, but serologic studies show that pregnant women are able to mount a protective immune response to vaccination (4, 5). In addition, several authors conclude that antibodies may be transmitted across the placenta to provide passive immunity to infants (4–7). In our review (2), we highlight several areas in which the state of current research is either inconclusive or could benefit from additional work. More studies of vaccine effectiveness and vaccine safety during pregnancy would be good additions to the literature. A safety study examining fetal viability after vaccination is especially important given the limitations of previous studies that have examined only livebirths, but the costs and methodological complexities associated with such a study may be prohibitive. Currently, no peer-reviewed scientific evidence indicates an association between the inactivated influenza vaccine and adverse maternal reactions, delivery complications, or poor fetal and newborn outcomes.
Although most adult influenza vaccine in the United States currently contains thimerosal, a mercury-containing preservative, the availability of thimerosal-free inactivated influenza vaccine is increasing (3, 8). This change may help lessen concerns about the safety of influenza vaccination during pregnancy and may in turn increase vaccination coverage rates among pregnant women.
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ACKNOWLEDGMENTS |
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Conflict of interest: none declared.
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References |
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 TOP References |
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- Ayoub DM and Yazbak EF. (2007) Re: "Delivering influenza vaccine to pregnant women." (Letter). Am J Epidemiol 165:351–2.
[Free Full Text] - Naleway AL, Smith WJ, Mullooly JP. (2006) Delivering influenza vaccine to pregnant women. Epidemiol Rev 28:47–53 (DOI: 10.1093/epirev/mxj002).
[Abstract/Free Full Text] - Harper SA, Fukuda K, Uyeki TM, et al. (2004) Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep 53:(RR-6)1–40.[Medline]
- Sumaya CV and Gibbs RS. (1979) Immunization of pregnant women with influenza A/New Jersey/76 virus vaccine: reactogenicity and immunogenicity in mother and infant. J Infect Dis 140:141–6.[Web of Science][Medline]
- Englund JA, Mbawuike IN, Hammill H, et al. (1993) Maternal immunization with influenza or tetanus toxoid vaccine for passive antibody protection in young infants. J Infect Dis 168:647–56.[Web of Science][Medline]
- Puck JM, Glezen WP, Frank AL, et al. (1980) Protection of infants from infection with influenza A virus by transplacentally acquired antibody. J Infect Dis 142:844–9.[Web of Science][Medline]
- Reuman PD, Ayoub EM, Small PA. (1987) Effect of passive maternal antibody on influenza illness in children: a prospective study of influenza A in mother-infant pairs. Pediatr Infect Dis J 6:398–403.[Web of Science][Medline]
- US Food and Drug Administration, Center for Biologics Evaluation and Research. Thimerosal in vaccines. Rockville, MD: Center for Biologics Evaluation and Research, 2006. (http://www.fda.gov/cber/vaccine/thimerosal.htm).
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