Flu Shot During Pregnancy Improves Perinatal Outcomes

Reading time: 4 – 6 minutes

During pregnancy, women need to take special care to avoid becoming ill. There are several reasons for this. The first is that a pregnant woman’s immune system is not as strong during pregnancy as it generally is; this helps to prevent the mother’s body from attacking the developing fetus. Unfortunately, however, the weakened immune system also means that pregnant mothers are more susceptible to pathogens that they’d otherwise fight off relatively easily. Increased susceptibility aside, there’s also the concern that some illnesses — influenza included — can impact the developing fetus. Finally, there’s the simple fact that many of the medications used to treat illnesses and their accompanying symptoms aren’t appropriate for pregnant women.

Currently, the American College of Obstetrics and Gynecology recommends flu shots during the fall and winter months for all pregnant women. This is an expansion of the previous policy, which recommended shots during later — but not earlier — pregnancy. The vaccination is important for helping to prevent influenza, to which pregnant women are particularly susceptible [1], and which can become particularly severe in pregnant women and increase the risk of pregnancy complications [2].

Several studies have shown that the flu shot is quite effective at preventing flu in pregnant women [3-5], and that the rate of adverse reactions to the flu shot is quite small, and no greater in pregnant than in non-pregnant women [6-8]. Further, a new study demonstrates that the benefits associated with flu shot during pregnancy extend to the developing fetus as well as to the mother. In a very large study of more than 55,000 pregnant mothers, those who received the flu shot during pregnancy were less likely to experience a number of negative birth outcomes [9]. These women were 27% less likely give birth significantly preterm, 19% less likely to have a very-small-for-gestational-age neonate, and 34% less likely to have a baby who died prenatally or perinatally. The study looked specifically at vaccination for the H1N1 influenza during a pandemic.

The authors concluded on the basis of these results that, while more research is needed in order to examine the mechanism for the improved birth outcomes, there is nevertheless evidence that influenza vaccination during pregnancy is associated with improved infant outcomes. Coupled with the recommendation of the American College of Obstetrics and Gynecology and the evidence that the flu shot is safe and effective during pregnancy, this is a powerful suggestion for routine influenza vaccination in pregnant women.

References

1. Jamieson et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet. 2009 Aug 8;374(9688):451-8. Epub 2009 Jul 28.
   View abstract
2. Reader et al. Influenza virus infection in the second and third trimesters of pregnancy: a clinical and seroepidemiological study. BJOG. 2000 Oct;107(10):1282-9.
   View abstract
3. Murray et al. Antibody response to monovalent A/New Jersey/8/76 influenza vaccine in pregnant women. J Clin Microbiol. 1979 Aug;10(2):184-7.
   View abstract
4. Sumaya et al. Immunization of pregnant women with influenza A/New Jersey/76 virus vaccine: reactogenicity and immunogenicity in mother and infant. J Infect Dis. 1979 Aug;140(2):141-6.
   View abstract
5. Zaman et al. Effectiveness of Maternal Influenza Immunization in Mothers and Infants. N Engl J Med. 2008 Oct 9;359(15):1555-64. Epub 2008 Sep 17.
   View abstract
6. Mak et al. Influenza vaccination in pregnancy: current evidence and selected national policies. Lancet Infect Dis. 2008 Jan;8(1):44-52.
   View abstract
7. Munoz et al. Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol. 2005 Apr;192(4):1098-106.
   View abstract
8. Tamma et al. Safety of influenza vaccination during pregnancy. Am J Obstet Gynecol. 2009 Dec;201(6):547-52. Epub 2009 Oct 21.
   View abstract
9. Fell et al. H1N1 Influenza Vaccination During Pregnancy and Fetal and Neonatal Outcomes. Am J Public Health. 2012 Jun;102(6):e33-40. Epub 2012 Apr 19.
   View abstract