There are two types of influenza viruses available in the United States: the trivalent inactivated influenza vaccine (TIV) and live attenuated influenza vaccine (LAIV). Both vaccines contain antigens of two influenza A viruses (H1N1 and H3N2) and an influenza B virus. TIV, or the "flu shot," contains antigens from killed influenza viruses; either split viruses or subunits of influenza viruses. LAIV, or "nasal spray" flu vaccine, contains attenuated (weakened) flu viruses that are cold-adapted, which means that the viruses replicate most efficiently at temperatures found in the upper respiratory tract.
The flu shot is recommended for pregnant women by the American College of Obstetricians and Gynecologists, the American Academy of Family Physicians, and the CDC’s Advisory Committee on Immunization Practices (ACIP). Inactivated influenza vaccine has been recommended for pregnant women since the 1960s. Since that time, numerous studies have assessed the safety of the flu shot for both mother and baby and none have found serious adverse effects for either mother or baby (ACOG, 2010; CDC, 2010; MacDonald et al., 2009; Moro et al. 2011; Tamma et al., 2009).
Because LAIV is a live-virus vaccine, there is a theoretical risk of infecting a fetus with the vaccine virus, so LAIV is not recommended for pregnant women. Although LAIV recipients can shed vaccine virus, pregnant women do not need to avoid people who have received the vaccine; in fact, pregnant women can safely administer LAIV (CDC, 2006). Postpartum and breastfeeding women may receive LAIV (CDC, 2010).
Newborn babies are protected from a number of diseases by antibodies that they receive from their mothers through the placenta (maternal antibodies can also interfere with a baby's immune response to vaccines). There is evidence that giving a flu shot to a pregnant woman protects her baby from influenza (Benowitz et al., 2010; Eick et al., 2011; Poehling et al., 2011; Zaman et al., 2008).
Side effects:The most common side effect of the flu shot is pain at the injection site. Other side effects include headache, muscle aches, and fever. The most common side effects of LAIV are runny nose, cough, and sore throat. Severe allergic reactions to flu vaccine are rare (CDC, 2010). The viruses for both TIV and LAIV are grown on chicken eggs. In general, flu vaccines are not contraindicated for people who can eat eggs. People with severe egg allergies should talk to a health care provider about flu vaccine (CDC, 2011).
There are a few more points I'd like to make about influenza vaccines, but I don't want my posts to run too long. Instead, I'll post a gratuitous picture of Holly's ultrasound from a couple of weeks ago:
American College of Obstetricians and Gynecologists. (2010). Influenza vaccination during pregnancy. Committee Opinion No. 468. Obstetrics & Gynecology, 116(4), 1006-1007. http://www.acog.org/Resources_And_Publications/Committee_Opinions/Committee_on_Obstetric_Practice/Influenza_Vaccination_During_Pregnancy.aspx.
Benowitz, I., Esposito, D. B., Gracey, K. D., Shapiro, E. D., & Vazquez, M. (2010).
Influenza vaccine given to pregnant women reduces hospitalization due to influenza in their infants. Clinical Infectious Diseases, 51(12), 1355-1361. http://cid.oxfordjournals.org/content/51/12/1355.full.
Centers for Disease Control and Prevention. (2006). Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices. Morbidity and Mortality Weekly Report, 55(10), 1-42. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5510a1.htm?s_cid=rr5510a1_e.
Centers for Disease Control and Prevention. (2010). Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices. Morbidity and Mortality Weekly Report, 59(8) 1-62. http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5908a1.htm.
Centers for Disease Control and Prevention. (2011). Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2011. Morbidity and Mortality Weekly Report, 60(33), 1128-1132. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6033a3.htm?s_cid=mm6033a3_w.
Eick, A. A., Uyeki, T. M., Klimov, A., Hall, H., Reid, R., Santosham, M. et al. (2011). Maternal influenza vaccination and effect on influenza virus infection in young infants. Archives of Pediatrics & Adolescent Medicine, 165(2), 104-111. doi:10.1001/archpediatrics.2010.192.
MacDonald, N. E., Riley, L. E., & Steinhoff, M. C. (2009). Influenza immunization in pregnancy. Obstetrics & Gynecology, 114(2, Part 1), 365-368. doi:10.1097/AOG.0b013e3181af6ce8.
Moro, P. L., Broder, K., Zheteyeva, Y., Walton, K., Rohan, P., Sutherland, A. et al. (2011). Adverse events in pregnant women following administration of trivalent inactivated influenza vaccine and live attenuated influenza vaccine in the Vaccine Adverse Event Reporting System, 1990-2009. American Journal of Obstetrics and Gynecology, 204(2), 146.e1-146.e7. doi:10.1016/j.ajog.2010.08.050.
Poehling, K.A., Szilagyi,P. G., Staat, M. A., Snively, B. M., Payne, D. C., Bridges, C. B. et al. (2011). Impact of maternal immunization on influenza hospitalizations in infants. American Journal of Obstetrics & Gynecology, 204(6 Supple. 1), S141-S148. http://www.ajog.org/article/S0002-9378(11)00232-8/fulltext.
Tamma, P. D., Ault, K. A., del Rio, C., Steinhoff, M. C., Halsey, N. A. & Omer, S. B. (2009). Safety of influenza vaccination during pregnancy. American Journal of Obstetrics and Gynecology, 201(6), 547-552. http://www.ajog.org/article/S0002-9378(09)01108-9/fulltext.
Zaman, K., Roy, E., Arifeen, S. E., Rahman, M., Raqib, R., Wilson, E. et al. (2008). Effectiveness of maternal influenza immunization in mothers and infants. New England Journal of Medicine, 359(15), 1555-1564. http://www.nejm.org/doi/full/10.1056/NEJMoa0708630.