DOI: 10.1111/1471-0528.12977

Systematic review

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Fetal death and preterm birth associated with maternal influenza vaccination: systematic review DB Fell,a,b RW Platt,a A Lanes,c K Wilson,d,e,f JS Kaufman,a O Basso,a D Buckeridgea a

Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, QC, Canada b Better Outcomes Registry & Network (BORN) Ontario, Ottawa, ON, Canada c Department of Epidemiology and Community Medicine, University of Ottawa, Ottawa, ON, Canada d Department of Medicine, University of Ottawa, Ottawa, ON, Canada e Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada f Institute for Clinical Evaluative Sciences, Ottawa, ON, Canada Correspondence: DB Fell, Better Outcomes Registry & Network (BORN) Ontario, Children’s Hospital of Eastern Ontario Research Institute, 401 Smyth Road, Centre for Practice Changing Research, Ottawa, Ontario, Canada K1H 8L1. Email [email protected] Accepted 13 May 2014. Published Online 10 July 2014.

Background Before 2012, few studies had addressed pregnancy

outcomes following maternal influenza vaccination; however, the number of publications on this topic has increased recently. Objectives To review comparative studies evaluating fetal death or

preterm birth associated with influenza vaccination during pregnancy. Search strategy We searched bibliographic databases from

inception to April 2014. Selection criteria Experimental or observational studies assessing

the relationship between influenza vaccination during pregnancy and fetal death or preterm birth. Data collection and analysis Two reviewers independently abstracted data from studies meeting the inclusion criteria. Main results We included one randomised clinical trial and 26

observational studies. Meta-analyses were not considered appropriate because of high clinical and statistical heterogeneity. Three studies of fetal death at any gestational age reported

adjusted effect estimates in the range 0.56–0.79, and four of five studies of fetal death at 75%) were deemed to be inappropriate for meta-analysis; however, we attempted to explain heterogeneity using random-effects meta-regression on study-level variables (i.e. vaccine type, study quality) when ten or more studies were available for a given outcome.36,37 As a result of concerns about bias in observational studies of influenza vaccine effectiveness,38 we only considered studies that reported an effect measure addressing confounding in the design (e.g. matching or randomisation) or analysis (e.g. multivariable regression) for possible meta-analysis. STATA SE 12.1 software (STATA-Corp LP, College Station, TX, USA) was used to generate Forest plots and for all analyses.

Results Bibliographic database searches identified 4446 titles and abstracts, corresponding to 2199 unique records following de-duplication. Of these, 1544 were not relevant to our review, 472 were editorials (e.g. commentaries and annual influenza vaccination recommendations), 102 were review articles, 30 had no comparison group (e.g. pharmacovigilance study) or an inappropriate comparison group (e.g. comparison of one influenza vaccine directly with another39) and five did not meet language criteria. We retrieved the full text for the remaining 45 articles, of which a further 18 were excluded for the reasons provided in Figure 1. Our full-text review included two conference abstracts for which we contacted the lead author to determine whether there were journal articles reporting the same study. One was a clinical trial of influenza vaccination during the third trimester in Mali (ClinicalTrials.gov identifier: NCT01430689), which was underway but incomplete,40 and the second was a Canadian prospective cohort study that

had not yet been published.41 Both were excluded for having ‘insufficient information’ (Figure 1). Four other conference abstracts were excluded as ‘duplicates’, as all were superseded by journal articles that had already been included in the full-text review.42–45 Finally, one PhD dissertation was identified and ultimately retained in our review after the author confirmed that the results had not been published elsewhere.30 We included 27 studies, four of which were published prior to 2012,46–49 and the remainder between 2012 and April 2014. One study was an RCT,43 three used a case–control design30,50,51 and 23 used cohort designs. Studies originated from 13 countries, with the majority performed in the USA (Table S3). Fourteen studies were of monovalent H1N1 vaccines,8,44,45,52–62 ten examined TIVs,30,42,43,46–50,63,64 and three51,65,66 did not distinguish between TIVs (with or without H1N1) and monovalent H1N1 vaccines (Table S1). Among the 26 observational studies, scores for the Newcastle–Ottawa Scale were in the range 5–9 (median 8.5; Table S3). The scores for the Downs–Black quality assessment tool were in the range 15–29 with a median value of 25. The major area of concern for the three studies with a low Downs–Black score (

Fetal death and preterm birth associated with maternal influenza vaccination: systematic review.

Before 2012, few studies had addressed pregnancy outcomes following maternal influenza vaccination; however, the number of publications on this topic ...
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