Maternal Influenza Vaccination and Effect on Influenza Virus Infection in Young Infants. Eick, etal. Arch Pediatr Adolesc Med. Published online October 4, 2010. doi:10.1001/archpediatrics.2010.192
Influenza vaccination program: effects on maternal health and pregnancy outcome. Deinard and Ogburn. Am J Obstet Gynecol, 140:240-5, 1981.
This most recent study was done on the Indian reservations in Navajo and White Mountain Apache areas. All 1,169 women who were a part of the study birthed during the influenza season. Among the infants whose mothers were vaccinated, there was a 41% reduction in the risk of laboratory-confirmed influenza virus infection in the babies compared with those whose mothers declined vaccination. At the same time the probability that any of these babies would be admitted to a hospital for treatment of flu or flu-like diseases went down by 39%. Evaluation of the babies’ blood samples showed a higher level of flu antibody titers in babies whose mothers had received vaccination against influenza during pregnancy. In addition they found significantly higher antibody titers in the 2- to 3-month-old infants who did not develop influenza compared to those who became ill.
This recent research parallels a study that is almost 30 years old. Those researchers found that if an expectant mother contracts influenza during her pregnancy (so-called natural immunization), then the chances that her baby will become infected with influenza is considerably lower especially in the initial six months after being born. The first six months are considered crucial with respect to the child’s health because the immune system of the newborn is not fully developed to ward off contagious diseases, and vaccination cannot be effectively administered during the first six months.
Dr. Albrecht’s Comments:
Studies have consistently identified the old and youngchildren and infants as well as pregnant women to be among those at the highest risk of influenza complications. Amonghealthy children younger than 5 years, annual influenza-associatedhospitalization rates are approximately 100 per 100,000,while children with underlying medical conditions have rates ofapproximately 500 per 100,000 in the United States. Influenza virus infection in infants is generally more frequentamong those aged 6 to 12 months than in the first 6 months oflife, potentially owing to the early protection conferred by maternalinfluenza antibodies acquired trans-placentally or through breastfeeding. However, during severe influenza seasons, morbidity and mortalityrates among infants younger than 6 months have been reportedto exceed those of older infants.
The US Advisory Committee on Immunization Practices recommendsthat pregnant women receive influenza vaccine because of theincreased risk of influenza complications in pregnant women. The findings in this study provide support for the added benefit of immunizing pregnant women for protecting their infants. This is especially important in the first 6 months of life when infants are not eligible for influenza vaccination but are at highest risk of severe influenza illness.
The exact mechanism by which vaccination of the mother conferred protection to the infant is not certain. It is probably due to maternal influenza antibodies being acquired transplacentally or through breastfeeding, or perhaps to reduced infant exposure to influenza illness from mothers who have been immunized. The take home message is get your influenza vaccination.