title: Risks and safety of pandemic H1N1 influenza vaccine in pregnancy: exposure prevalence, preterm delivery, and specific birth defects.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Slone Epidemiology Center at Boston University, Boston, MA, United States; Vaccines and Medications in Pregnancy Surveillance System (VAMPSS), United States. Electronic address: clouik@bu.edu.
authors.forename: Carol
authors.initials: C
authors.lastname: Louik
authors.forename: Katherine
authors.initials: K
authors.lastname: Ahrens
authors.forename: Stephen
authors.initials: S
authors.lastname: Kerr
authors.forename: Junhee
authors.initials: J
authors.lastname: Pyo
authors.forename: Christina
authors.initials: C
authors.lastname: Chambers
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Jones
authors.forename: Michael
authors.initials: M
authors.lastname: Schatz
authors.forename: Allen A
authors.initials: AA
authors.lastname: Mitchell
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D000013:Congenital Abnormalities / Q000453:epidemiology*; D062665:Epidemiological Monitoring; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects*; D007251:Influenza, Human / Q000517:prevention & control; D011247:Pregnancy; D011264:Pregnancy Trimesters; D047928:Premature Birth / Q000453:epidemiology*; D015995:Prevalence; D012306:Risk; D014481:United States; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Birth defects; Pandemic H1N1 vaccine; Pregnancy; Preterm delivery