Maternal immunization with inactivated influenza vaccine: rationale and experience
Introduction
Inactivated influenza vaccine is currently recommended for the prevention of influenza disease in high-risk populations within the United States. Populations for whom the vaccine is currently recommended include those healthy persons aged 50 years and older, residents of chronic care facilities, individuals with chronic pulmonary and cardiovascular disease, including asthma, metabolic diseases, renal disease, hemoglobinopathies, immunosuppressed individuals, and women who will be in the second or third trimester of pregnancy during influenza season [1]. The use of influenza vaccine during pregnancy was routine during the 1950s and 1960s, but was not recently included in official recommendations until 1997 [2]. Currently, at least two vaccines are recommended for routine use in pregnant women if medically indicated: tetanus toxoid vaccine and trivalent inactivated influenza virus vaccine (TIV) [3]. Other vaccines recommended to be administered to pregnant women under special circumstances include polysaccharide vaccines, such as pneumococcal polysaccharide vaccine and meningococcal polysaccharide vaccine, as well as inactivated viral vaccines such as hepatitis A and B, rabies virus, or inactivated poliovirus vaccines [3]. All of these vaccines have the benefit of protecting the pregnant women from serious disease during pregnancy or the postpartum period, and giving potential benefit for the fetus and neonate with no known or reported risks.
Use of any vaccine in pregnant women should be carefully considered. Obstetricians and family practitioners provide much of the point of contact for the use of any vaccine during pregnancy, and in general do not advocate the use of any medical intervention unless indicated. A working group of the American College of Obstetrics and Gynecology (ACOG) has developed guidelines for immunization during pregnancy. These considerations include documentation that women in the category considered for immunization have a high risk for exposure to disease, that infection with the infectious agent poses a special risk to the mother, that the infection poses a special risk to the fetus, and a vaccine is available which is unlikely to cause harm [4]. This paper will address these considerations, and summarize studies and reports evaluating the safety and immunogenicity of inactivated influenza vaccine in this population.
Section snippets
Risk of influenza in pregnant women
The overall risk of exposure of pregnant women to influenza is high. Influenza is known to infect approximately 10% of adults and up to 30% of children annually [5]. Women in the childbearing age range have increased exposure to young children, who have an increased risk of becoming infected with influenza. These women are likely to have an increased rate of exposure compared to the general adult population. In one serological study which prospectively evaluated over 1500 pregnant women for
Impact of influenza on the fetus and infant
Influenza in pregnant women during the pandemics of 1918 and 1957 was associated with pneumonia. In half the cases of influenza pneumonia in pregnant women, pregnancy was interrupted due to spontaneous abortion or delivery [7], [8]. Numerous case reports of stillbirths and neonatal deaths associated with maternal infection (often associated with the death of the mother) have been reported since that time [10], [11], [13], [17], [18], [19]. However, the documentation of these statistics with the
Transplacentally-acquired antibody
Infants are protected from symptomatic influenza A virus infection by transplacentally-acquired antibody. One prospective study carried out at Baylor College of Medicine prospectively collected cord blood at delivery and followed infants during the succeeding respiratory virus season to demonstrate protection from serious disease in those infants with higher cord antibody levels [28]. Another prospective study enrolled 158 mother–infant pairs at birth to demonstrate that passive maternal
Practical aspects of immunization with influenza during pregnancy
Although routine immunization of pregnant women during the latter two trimesters of pregnancy is recommended by advisory groups and the CDC [1], [36], this practice is not implemented in many clinical settings. Current data estimates that <10% of pregnant women who are at highest risk for influenza during pregnancy receive influenza vaccine, compared to nearly 16% of nonpregnant females in the same age group, or 66% of individuals over the age of 65, or 5–32% of children with reactive airway
Summary of available data
Available data clearly indicate that pregnant women are at increased risk for influenza-related complications, and these complications include conditions that may put the unborn fetus at some risk. Safety of this vaccine in the pregnant woman has been established, and increasing vaccine use during pregnancy has the potential to benefit both the woman and her infant.
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