Background: Influenza vaccination during pregnancy is the primary intervention to protect pregnant women, their fetus and infant from influenza infection. The World Health Organization recommends that countries expanding or initiating influenza immunization programs should consider pregnant women as the highest priority group. However, it is considered to be an expensive public health measure and data on the effectiveness and safety of the vaccine has been lacking and inconsistent. Evidence of the vaccine's effectiveness and safety is critical to the decision making process of governments and policy-makers, as well as clinicians and pregnant women.
Objectives: To synthesize the best available evidence on the effectiveness and safety of influenza vaccination during pregnancy for pregnant women, their fetus and infant up to six months of age.
Inclusion criteria
Types of participants
Pregnant women with or without risk factors for complications from influenza infection, their fetus and infants up to the age of 6 months.
Types of intervention
Inactivated influenza vaccination, irrespective of antigenic configuration or adjuvant, administered via any route and any dose, to pregnant women of any trimester.
Types of studies
Studies using quantitative research methods were considered for this systematic review.
Types of outcomes
This systematic review considered studies that reported on the effectiveness of maternal influenza vaccination at reducing the rate and severity of influenza and influenza-like illness for pregnant women and infants up to six months of age. The review also investigated the safety outcomes for pregnant women and fetus following influenza vaccination during pregnancy. Outcomes for pregnant women included both adverse events and serious adverse events. For the fetus, outcomes included spontaneous abortion, fetal death, premature birth, low birth weight, small for gestational age and congenital malformation.
Search strategy: An extensive search of the literature was undertaken to find both published and unpublished English language studies between the inception of each database to March 2014.
Methodological quality: Papers selected for retrieval were assessed by two independent reviewers for methodological validity prior to inclusion in the review.
Data collection: Data were extracted from included papers using data extraction tools developed by the Joanna Briggs Institute.
Data synthesis: Data were, where possible, pooled in statistical meta-analysis. Where statistical pooling was not possible the findings were presented in narrative and table form.
Results: A total of 46 relevant studies were included in the review following critical appraisal. Birthing and fetal outcomes were included from 23 studies and adverse event outcomes for pregnant women from 28 studies. The effectiveness of maternal influenza vaccination in reducing illness in pregnant women and infants up to six months included outcomes from another 10 studies.
Conclusions: Influenza vaccine administered during pregnancy is effective and provides a similar reduction in influenza-like illness as it does for a healthy adult population. Despite this, there is no evidence on the effectiveness of the influenza vaccine at reducing severe illness or hospitalization in pregnant women. Infants of pregnant women vaccinated during their second or third trimester can expect to have reduced rates of influenza and influenza-related hospitalization, for their first six months of life.
Influenza vaccination during pregnancy had no association with adverse outcomes for the fetus including premature birth, small for gestational age, congenital malformation, spontaneous abortion and fetal death.