Risks and safety of pandemic H1N1 influenza vaccine in pregnancy: Exposure prevalence, preterm delivery, and specific birth defects

Vaccines and Medications in Pregnancy Surveillance System (VAMPSS), United States. Electronic address: .
Vaccine (Impact Factor: 3.62). 09/2013; 31(44). DOI: 10.1016/j.vaccine.2013.08.096
Source: PubMed


We estimated exposure prevalence and studied potential risks for preterm delivery (PTD) and specific birth defects associated with exposure to the unadjuvanted pH1N1-containing vaccines in the 2009-2010 and 2010-2011 influenza seasons. We used data from 4 regional centers in the United States collected as part of the Slone Epidemiology Center's Birth Defects Study. For PTD, propensity score-adjusted time-varying hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated for exposure anytime in pregnancy and for each trimester. For 41 specific major birth defects, propensity score-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated. Among 4191 subjects, there were 3104 mothers of malformed (cases) and 1087 mothers of nonmalformed (controls). Exposure prevalences among controls were 47% for the 2009-2010 season and 38% for the 2010-2011 season; prevalence varied by geographic region. Results for PTD differed between the two seasons, with risks above and below the null for the 2009-2010 and 2010-2011 seasons, respectively. For 41 specific birth defects, most adjusted ORs were close to 1.0. Three defects had adjusted ORs>2.0 and four had risks<0.5; however, 95% CIs for these were wide.
Among women exposed to pH1N1 vaccine, we found a decreased risk for PTD in the 2010-2011 season; risk was increased in 2009-2010, particularly following exposure in the first trimester, though the decrease in gestational length was less than 2 days. For specific major defects, we found no meaningful evidence of increased risk for specific congenital malformations following pH1N1 influenza vaccinations in the 2009-2010 and 2010-2011 seasons.

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    ABSTRACT: There is a need for additional information on the fetal risks and relative safety of the pandemic H1N1 monovalent or trivalent influenza (pH1N1)-containing vaccines in women exposed during pregnancy. To assess risks and relative safety of the pH1N1-containing vaccines, we conducted a prospective cohort study of pH1N1-vaccine-exposed and unexposed comparison women residing in the U.S. or Canada who were recruited during pregnancy and followed to outcome between October 2009 and August 2012. For exposure to the pH1N1 vaccine, adjusted relative risks (RRs) and 95% confidence intervals (CIs) were estimated for major birth defects and infants small for gestational age. Adjusted hazard ratios (HRs) and 95% CIs were estimated for spontaneous abortion and preterm delivery for time-varying exposure. There were 1032 subjects available for analysis; 841 women were exposed to a pH1N1-containing vaccine in pregnancy, and 191 women were unexposed to any influenza vaccine in pregnancy. Nine of 328 (2.7%) first-trimester-exposed pregnancies resulted in an infant with a major birth defect compared to 6/188 (3.2%) in the unexposed (adjusted RR 0.79, 95% CI 0.26-2.42). The HR for spontaneous abortion was not elevated (adjusted HR 0.92, 95% CI 0.31-2.72). Adjusted HRs for preterm delivery were elevated for exposure anytime in pregnancy (3.28, 95% CI 1.25-8.63), specifically with exposure in the 1st or 2nd trimester. However, the mean decrease in gestational age in the exposed pregnancies was approximately three days. Adjusted RRs for small for gestational age infants on weight and length approximated 1.0. For the 2009-12 influenza seasons combined, we found no meaningful evidence of increased RR or HR for major birth defects, spontaneous abortion, or small for gestational age infants. There was some evidence of an increased HR for preterm delivery following pH1N1-influenza vaccine exposure; however the decrease in gestational age on average was approximately three days.
    Vaccine 09/2013; 31(44). DOI:10.1016/j.vaccine.2013.08.097 · 3.62 Impact Factor
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    ABSTRACT: Vaccination during pregnancy with certain vaccines can prevent morbidity and mortality in pregnant women and their infants. However, previous recommendations often focused on the potential risks of vaccines to the fetus when used during pregnancy. In recent years, additional data have become available on the absence of increased risks for adverse events associated with vaccines when administered during pregnancy and on their benefits to mothers and infants. Currently two vaccines - (i) inactivated influenza, and (ii) tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) - are recommended for use by all pregnant women by the United States Advisory Committee on Immunization Practices. Here we review the history of vaccination during pregnancy, the current status of recommendations for vaccination during pregnancy in the USA, and the potential for future advances in this area, including key barriers that must be overcome to accommodate these advances.
    Seminars in Fetal and Neonatal Medicine 12/2013; 19(3). DOI:10.1016/j.siny.2013.11.014 · 3.03 Impact Factor
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