Assessing the safety of influenza immunization during pregnancy: The Vaccine Safety Datalink
HealthPartners Institute for Education and Research, Minneapolis, MN, USA.American journal of obstetrics and gynecology (Impact Factor: 4.7). 09/2012; 207(3 Suppl):S47-51. DOI: 10.1016/j.ajog.2012.06.073
The influenza vaccine can reduce maternal and neonatal morbidity and mortality and thus is recommended for all pregnant women. However, concerns regarding safety of influenza vaccine remain a barrier to vaccination. We describe ongoing analyses of influenza vaccine safety during pregnancy within the Vaccine Safety Datalink that includes the evaluation of acute events, adverse pregnancy and birth outcomes, and congenital anomalies. In addition, we highlight unique challenges and strategies for the study of vaccine safety among pregnant women with the use of large linked databases.
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ABSTRACT: Objective: To estimate the risks for medically attended events occurring within 42 days of receiving trivalent inactivated influenza vaccine and to evaluate specific risks of first-trimester vaccination. Methods: This retrospective observational cohort study compared rates of medically attended adverse events in trivalent inactivated influenza-vaccinated and unvaccinated pregnant women in the Vaccine Safety Datalink. Using a Poisson distribution and log link, we calculated maternal adjusted incident rate ratios for composite safety outcomes for the full cohort and the subset vaccinated during the first trimester. Results: The cohort included 75,906 vaccinated (28.4% in the first trimester) and 147,992 unvaccinated women matched by age, site, and pregnancy start date. In the first 3 days after vaccination, trivalent inactivated influenza vaccine was not associated with increased risk of specified medically attended events, including allergic reactions, cellulitis, and seizures (full cohort adjusted incident rate ratio 1.12, 95% confidence interval [CI] 0.81-1.55; P=.48; first-trimester adjusted incident rate ratio .97, 95% CI 0.53-1.78; P=.93). In the first 42 days, no incident cases of Guillain-Barré syndrome, optic neuritis, transverse myelitis, or Bells palsy were identified. Trivalent inactivated influenza vaccine was not associated with thrombocytopenia (full cohort adjusted incident rate ratio 0.90, 95% CI 0.68--1.19; P=.45; first-trimester adjusted incident rate ratio 0.56, 95% CI 0.22-1.39; P=.21) or an acute neurologic event (full cohort adjusted incident rate ratio 0.92, 95% CI 0.54-1.6; P=.75; first-trimester adjusted incident rate ratio 1.05, 95% CI 0.46-2.38; P=.91). Conclusions: Receipt of trivalent inactivated influenza vaccine during pregnancy was not associated with increased risk of adverse events in the 42 days after vaccination, supporting its safety for the mother.
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ABSTRACT: Background: The need for research on the safety of vaccination during pregnancy is widely recognized. Large, population-based data systems like the Vaccine Safety Datalink (VSD) may be useful for this research, but identifying pregnancies using electronic medical record (EMR) and claims data can be challenging. Methods: We modified an existing data processing algorithm to identify pregnancies within seven of the ten VSD sites. We validated the algorithm by calculating the agreement in pregnancy outcome type, end date, and gestational age between the algorithm and manual medical record review. At each participating site, we randomly sampled 15 episodes within four outcome type strata (live births, spontaneous abortions, elective abortions, and other pregnancy outcomes) for a total of 60 episodes per site. We also developed and validated methods to link mothers to their infants in the electronic data. Results: We identified 595,929 pregnancy episodes ending in 2002 through 2006 among women 12 through 55 years of age. Of these pregnancies, 75% ended in live births, 12% in spontaneous abortions, and 9% in elective abortions. We were able to confirm a pregnancy within 28 days of the algorithm-estimated pregnancy start date for 99% of live births, 93% of spontaneous abortions, 92% of elective abortions, and 90% of other outcomes sampled. The agreement between the algorithm-identified and the abstractor-identified outcome date ranged from 70% (elective abortion) to 96% (live birth) depending on outcome type. When gestational age was available in the EMR, agreement ranged from 82% (other) to 98% (live birth) depending on outcome type. We confirmed 100% of the 350 sampled mother-infant linkages with manual medical record review. Conclusions: The VSD algorithm accurately identifies pregnancy episodes and mother-infant pairs across participating sites. Additional manual record review may be needed to improve the precision of the pregnancy date estimates depending on specific study needs. These algorithms will allow us to conduct large, population-based studies of the safety of vaccination during pregnancy.
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