The World Health Organization recommends immunisation of pregnant women with inactivated influenza vaccine to reduce the risks associated with influenza infection in mothers and infants; however, the vaccine is not licensed for infants under 6 months of age.

This prospective blinded randomised controlled trial assessed the safety and immunogenicity of pneumococcal vaccine (control group) and the clinical efficacy of influenza vaccine on influenza illness in mothers and infants. The primary outcome in infants was the first episode of laboratory-confirmed influenza before 24 weeks of age. Other outcomes included fever >38°C with or without episodes of respiratory illness.

Three hundred and forty women in the third trimester of pregnancy were randomised. Most were followed through pregnancy and delivery until the infant was 24 weeks old; 172 mothers received the influenza vaccine and 168 the pneumococcal vaccine. There were 56 episodes of respiratory illness with fever in the maternal influenza group compared with 77 in the control group, reducing the incidence by 36%. Among the infants whose mothers received influenza vaccine (n = 159), six had laboratory-confirmed influenza compared with 16 (out of 157 infants) in the control group, reducing the incidence by 63%. There was a 29% reduction in the rate of infant respiratory illness with fever, 42% reduction in infant clinic visits for respiratory illness with fever and 49% reduction in clinician testing for influenza.

Maternal influenza vaccination prevents influenza infection in both the mother and infant. Five pregnant women would need to be vaccinated to prevent one case of respiratory illness and fever in a mother or infant. This system may be of benefit in regions with limited financial resources.

▸ Zaman K, Roy E, Arifeen SE, et al. Effectiveness of maternal influenza immunization in mothers and infants. N Engl J Med 2008;359:1555–64.