Maternal influenza immunisation in resource-limited settings

Abstract

Pregnant women and young infants are at high risk of developing severe infl uenza. 1,2 Among infants, those younger than 6 months have the highest risk of developing complications associated with infl uenza; 3 however, antiviral treatments and infl uenza vaccines are not approved in this age group. Given that infl uenza vaccines administered to pregnant women have shown a good safety profi le 4 and effi cacy to prevent infl uenza in infants younger than 6 months, 5,6 maternal immunisation seems to be an important strategy to protect both pregnant women and their infants. WHO targets seasonal infl uenza vaccination of pregnant women as a high priority. 7 Most high-income countries recommend maternal infl uenza immunisation to reduce the burden of infl uenza in the pregnant woman and her infant. 8 However, additional data are needed to support decisions about introduction of infl uenza vaccine in pregnant women in resource-limited settings. The Bill & Melinda Gates Foundation funded three large trials in South Africa, Mali, and Nepal, with the objective of increasing the evidence base for the eff ect of maternal infl uenza immunisation. 9 In The Lancet Infectious Diseases, Milagritos D Tapias and colleagues 10 report results of the trial done in Mali—a poorly-resourced country with high infant and maternal mortality. This is the largest randomised controlled trial evaluating the effi cacy, safety, and immuno genicity of trivalent inactivated infl uenza vaccine administered to third-trimester pregnant women to prevent infl uenza in infants younger than 6 months. 4193 women were immunised: 2018 with tri valent inactivated infl uenza vaccine and 2085 with conjugate quadrivalent meningococcal vaccine. Vaccine effi cacy against fi rst-episode laboratory confi rmed infl uenza in infants (the primary outcome) was 33·1% (95% CI 3·7–53·9) in infants born to women immunised at any time prepartum (intention-to-treat analysis), and 37·3% (7·6–57·8) in those born to women vaccinated at least 14 days prepartum (per-protocol analysis). Among participating women, vaccine effi cacy was 70·3% (95% CI 42·2–85·8) overall, 76·6% (28·4–94·3) in pregnant women, and 70·1% (28·0–89·1) in the post-partum period. There was no benefi cial eff ect of the trivalent inactivated infl uenza vaccine on birthweight. The technical and logistical feasibility of implementation of a new maternal immunisation programme was also shown with a high rate of recruitment among eligible women. Evidence of the effi cacy of maternal infl uenza immunisation to prevent infl uenza in infants in low-income countries from this trial is convincing and in agreement with fi ndings from the two previously reported randomised trials from Bangladesh (63% vaccine effi cacy, 95% CI 5–85) 5 and South Africa (48·8%, 11·6–70·4).