Influenza epidemiology and immunization during pregnancy: Final report of a World Health Organization working group

Abstract

From 2014 to 2017, the World Health Organization convened a working group to evaluate influenza disease burden and vaccine efficacy to inform estimates of maternal influenza immunization program impact. The group evaluated existing systematic reviews and relevant primary studies, and conducted four new systematic reviews. There was strong evidence that maternal influenza immunization prevented influenza illness in pregnant women and their infants, although data on severe illness prevention were lacking. The limited number of studies reporting influenza incidence in pregnant women and infants under six months had highly variable estimates and underrepresented low- and middle-income countries. The evidence that maternal influenza immunization reduces the risk of adverse birth outcomes was conflicting, and many observational studies were subject to substantial bias. The lack of scientific clarity regarding disease burden or magnitude of vaccine efficacy against severe illness poses challenges for robust estimation of the potential impact of maternal influenza immunization programs.

Characteristics and outcomes of pregnant women hospitalised with confirmed SARS-CoV-2 infection in the UK: a national cohort study using the UK Obstetric Surveillance System (UKOSS)

“…This supports the current guidance for strict social distancing measures amongst pregnant women, particularly in their third trimester 2 . It should be noted, however, that higher hospitalisation rates in the third trimester were also reported in the context of influenza, 31 and thought to be for precautionary reasons, rather than necessarily because of maternal compromise. Although case notification has been augmented through a link with the UK Early Pregnancy Surveillance System (UKEPSS), 32 it is also possible that the route of identification of the cases included in this series, through UK obstetric units, has led to under-ascertainment of women admitted in the early stages of pregnancy.…”

The safety of inactivated influenza vaccines in pregnancy for birth outcomes: a systematic review

“…Adjusted Odds Ratio inform estimates of maternal influenza immunisation programs. 69 Of the 40 included studies in this review, only 15 contained brand specific information. In addition, only 13 specified use of adjuvanted vaccines and 6 non-adjuvanted vaccines.…”

Immunogenicity and safety of a quadrivalent inactivated influenza vaccine in pregnant women: a randomized, observer-blind trial

“…Pregnant women and young infants are among the population subgroups at greatest risk of severe illness, complications, and death from influenza. 1,2 Hospital admissions for influenza illness are more frequent among pregnant women than nonpregnant women, 3,4 and influenza in young infants frequently leads to hospitalization, 5 bacterial co-infections, 6,7 and a higher mortality rate than in older children. 8 Severe influenza illness during pregnancy has also been associated with preterm birth and fetal death in the 2009 influenza A/H1N1 pandemic.…”

“…1 The World Health Organization (WHO) 1 and other advisory bodies [10][11][12] recommend that pregnant women are prioritized for influenza vaccination, since this provides both direct protection to pregnant women and indirect protection to their infants via transplacental maternal antibody transfer. 2,[13][14][15][16] This strategy is especially important for preventing influenza illness in infants aged less than 6 months because influenza vaccines are not licensed for use in this age group.…”