UK maternal influenza immunization rates are still subpar

Takeaway

• Administering inactivated influenza vaccine to pregnant women prevents laboratory-confirmed influenza infection, hospitalizations in infants aged <6 months, even in seasons with drifted strain circulation. 
• Related editorial.

Why this matters

• Encourage inactivated influenza vaccine uptake in pregnant women to prevent infant influenza, influenza-related hospitalizations.
• Reinforce that maternal vaccination protects young infants through transplacental antibody transfer. 

Key results

• 37 infants had confirmed influenza in 2013-2014 and 81 did in 2014-2015. 
• 19% and 25% had vaccinated mothers in these respective time frames. 
• Overall vaccine uptake was 45.2% and 49.2% for these years.
• Vaccine effectiveness (VE) was 70% (95% CI, 26%-88%) in 2013-2014 and 50% (95% CI, 12%-78%) in 2014-2015. 
• By strain: in 2014-2015, VE was 50% (95% CI, 11%-72%), antigenetically/genetically mismatched, A(H3N2)-dominant vs in 2013-2014, when VE was 66% (95% CI, 18%-84%), matched A(H1N1)pdm09-dominant. 
• Overall VE adjusted for week, season, region, ethnicity was 66% (P=.46).

Study design

• Retrospective cohort analysis reassessing maternal seasonal influenza vaccination for preventing influenza, influenza-related hospitalizations in UK infants aged <6 months, 2013-2014.
• Database: Clinical Practice Research Datalink pregnancy registry.
• Funding: National Institute for Health Research.

Limitations

• Retrospective.
• Residual confounding. 
• VE covariates limited by data availability.