pcb Chambers 2013.
| Methods | Prospective cohort study. The study has been carried out within the Organization of Teratology Information Specialists (OTIS) Research Group studies, whose aim is to evaluate the occurrence of pregnancy outcomes following an exposure to a medication or vaccine administered during pregnancy. OTIS services are located in academic institutions or hospitals throughout the US and Canada and provide counselling to about 70,000 callers annually who present with questions about the risks of exposures in pregnancy. Among these women, exposed and not exposed (comparison group) to the agent of interest are included in the study. In the present pH1N1 vaccine study, participants were enrolled between October 2009 and April 2012 and were exposed or not exposed to either the monovalent (2009–10 season) or trivalent (2009–12 seasons) pH1N1 vaccine in 1 of 3 influenza seasons. Information about exposure and outcomes of exposed and unexposed cohort were assessed by means of phone questionnaires. | |
| Participants | 841 pregnant women exposed to a pH1N‐containing vaccine 191 not exposed pregnant women |
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| Interventions | Information about vaccine type, date of vaccination, and medical setting where immunisation took place are present in the OTIS questionnaires. Participants were further asked to verify provided information on their vaccination record (when available) or to give permission to contact the participant’s provider to obtain this information. In cases where the vaccine was given in a non‐traditional setting, an attempt was made to determine the specific product used and the date and location of vaccine administration. The timing of vaccine exposure was divided into 4 categories:
In the 2009–10 season, some women received the 2009–10 seasonal vaccine (not containing the pH1N1 strain) prior to the pH1N1 monovalent vaccine becoming available, and were subsequently vaccinated with the monovalent pH1N1 vaccine. These women were classified as pH1N1 vaccine exposed; however, previous receipt of the non‐pandemic vaccine was considered a covariate. The comparison group consisted of women who received no influenza vaccine of any type throughout their pregnancy. Vaccines were monovalent pH1N1 (unspecified) in 2009‐10, and pH1N1‐containing TIV in 2010‐11 and 2011‐12. |
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| Outcomes | Outcomes were collected in the OTIS questionnaire (maternal interview) and medical records obtained from obstetrician, paediatrician, and delivery hospital. Ultrasound dating was used to correct gestational weeks as necessary using a standard algorithm, or if the LMP was unknown. The following definitions were used:
Analysis for the first 3 outcomes was performed considering timing of exposure. Crude and adjusted HH or OR estimate is provided, other than crude data. |
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| Notes | Funding source ‐ government This project has been funded in whole or in part with Federal funds from the Office of the Assistant Secretary for Preparedness and Response, Biomedical Advanced Research and Development Authority, Department of Health and Human Services, under Contract No. HHS0100201000029C and the OTIS Collaborative Research Group. |
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| Risk of bias | ||
| Bias | Authors' judgement | Support for judgement |
| PCS/RCS ‐ selection exposed cohort All outcomes | Low risk | Quite a representative sample of pregnant women enrolled in the OTIS registers |
| PCS/RCS ‐ selection non‐exposed cohort All outcomes | Low risk | Drawn from the same source as the exposed cohort |
| PCS/RCS ‐ comparability All outcomes | Unclear risk | Possible confounding factors have been taken into account. |
| PCS/RCS ‐ assessment of outcome All outcomes | Low risk | Secure records |
| Summary assessment | Low risk | Low risk of bias |