Figure 1.

Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) flow diagram showing study selection process. ^aDescriptive studies and systematic reviews were screened as part of the overall evidence review, but are not reported in this publication. ^bYates et al. (2010)32 and Pierce et al. (2011)33 used the same study population, the former representing an earlier version of the study, published before full follow‐up had been completed. Only the Pierce et al. study33 is reported in this review. ^cSubsequent to the original screening, a placebo‐controlled randomised clinical trial (RCT) of influenza immunisation during pregnancy was included.11