Effectiveness of maternal influenza immunization in mothers and infants. Zaman K, Roy E, Arifeen SE, et al. 2008. New Engl J Med 359: 1555-64.
Does influenza immunization of pregnant women protect the mother and her infant against influenza?
This trial included 340 women in the third trimester of pregnancy. It was conducted in Dhaka, Bangladesh between August 2004 and May 2005.
Mothers were immunized with either trivalent inactivated influenza virus vaccine (TIV) or 23-valent pneumococcal polysaccharide vaccine (PPS). Mothers who had a history of systemic disease, previous complicated pregnancy or preterm delivery, abortion, congenital anomaly, or hypersensitivity to one of the vaccines, were excluded. All mothers were interviewed for adverse events at 8, 24, 48, and 72 hours and then at one week after immunization.
The researchers followed each mother from 2 weeks after immunization through pregnancy and delivery and then she was interviewed weekly about her child’s illnesses from birth through 24 weeks of age. Mothers were given digital thermometers and were asked to bring their infants to the study clinic for illness where clinicians assessed the children for acute febrile respiratory illness and collected throat swabs for detection of influenza virus antigens. Surveillance for influenza virus in Dhaka showed evidence of influenza virus activity during 10 of the 11 months of the study.
Minor local and systemic adverse reactions were similar in both groups, although mothers who received the pneumococcal vaccine (PPS) experienced more local pain at the site of injection.
Mothers who received influenza vaccine (TIV) were less likely to have febrile respiratory illness compared with those who received PPS. Maternal TIV immunization reduced the rates of febrile respiratory illnesses, clinic visits for febrile respiratory illnesses, and of laboratory-confirmed influenza febrile illnesses in their infants. The data suggested that maternal TIV immunization might protect infants for up to 5 to 6 months of age.
Immunization of pregnant women reduced febrile respiratory illnesses in both the mothers and her newborn infant. Culture proven illness was reduced by 63% in infants up to 6 months of age and prevented about one third of illnesses in both the mother and infant.
Maternal immunization with influenza vaccine is a strategy with substantial benefits for both mothers and infants. Although this study did not study a large enough group of patients to be able to evaluate whether maternal TIV immunization affected the rates of severe influenza—such as illnesses that led to hospitalization—the substantial reduction of febrile respiratory illnesses in both mothers and children would suggest that this might well be the case.