Methods: Cases (women with SAB) and controls (women with live births or stillbirths) were identified using administrative, clinical, and claims data; medical records were abstracted to confirm pregnancy, vaccinations, and estimate the SAB date. Cases and controls were matched on VSD site, last menstrual period, and age (<30, ≥30 years). The primary exposure was IIV in the 1-28 days before SAB; two other risk windows (29-56 and >56 days) were also evaluated. The analysis adjusted for age and other potential confounders. A post-hoc analysis assessed whether vaccination in the prior season modified the association between IIV and SAB.
Results: The analysis included 485 matched pairs. The adjusted odds ratio (aOR) was 2.0 (95% CI 1.1-3.6) for IIV in the 1-28 days before SAB compared to unvaccinated women; there was no association in the other risk windows. In season-specific analyses, the aOR in the 1‑28 days was 3.7 (95% CI 1.4-9.4) in 2010-11 and 1.4 (95% CI 0.6-3.3) in 2011-12. Among all women who received pH1N1-containing vaccine in the influenza season prior to study entry, the aOR in the 1-28 days was 7.7 (95% CI 2.2-27.3); the aOR was 1.3 (95% CI 0.7-2.7) among women not vaccinated in the prior season (P=0.02 for effect modification). This effect modification due to prior season vaccination was observed in each season. There was no association in the other risk windows regardless of past exposure to pH1N1-containing vaccine.
Conclusion: In the primary analysis that included two influenza seasons, SAB was associated with IIV in the 1‑28 days before SAB; the elevated risk was confined to women who also received pH1N1-containing vaccine in the prior season. The overall association between IIV and SAB in the 1-28 days was significant in 2010-11, but not in 2011‑12. However, the elevated risk among women previously vaccinated with pH1N1-containing vaccine was observed in each season.
J. King, None
F. Destefano, None
M. Mascola, None
S. Irving, None
C. Cheetham, None
J. Glanz, None
L. A. Jackson, None
N. P. Klein, GSK: Grant Investigator , Research grant
Sanofi Pasteur: Grant Investigator , Research grant
Pfizer: Grant Investigator , Research grant
Merck: Grant Investigator , Research grant
Novartis: Grant Investigator , Research grant
Nuron Biotech: Grant Investigator , Research grant
Protein Science: Grant Investigator , Research grant and Research support
MedImmune: Grant Investigator , Research grant
A. Naleway, GlaxoSmithKline: Investigator , Research support
E. Weintraub, None
E. Belongia, Medimmune: Investigator , Research support