Abstract
BackgroundVarious studies have shown that infants under the age of 6 months are especially vulnerable for complications due to influenza. Currently there are no vaccines licensed for use in this age group. Vaccination of pregnant women during the last trimester, recommended by the WHO as protective measure for this vulnerable female population, may provide protection of newborns at this early age. Although it has been observed that maternal vaccination can passively transfer protection, maternal antibodies could possibly also interfere with subsequent active vaccination of the offspring.MethodsUsing a mouse model, we evaluated in depth the ability of maternal influenza vaccination to protect offspring and the effect of maternal immunization on the subsequent influenza vaccination of the offspring. By varying the regimen of maternal immunization we explored the impact of different levels of maternal antibodies on the longevity of these antibodies in their progeny. We subsequently assessed to what extent maternal antibodies can mediate direct protection against influenza in their offspring, and whether these antibodies interfere with protection induced by active vaccination of the offspring.ResultsThe number of immunizations of pregnant mice correlates to the level and longevity of maternal antibodies in the offspring. When these antibodies are present at time of influenza challenge they protect offspring against lethal influenza challenge, even in the absence of detectable HAI titers. Moreover, no detectable interference of passively-transferred maternal antibodies on the subsequent vaccination of the offspring was observed.ConclusionIn the absence of a licensed influenza vaccine for young children, vaccination of pregnant women is a promising measure to provide protection of young infants against severe influenza infection.
Highlights
Various studies have shown that infants under the age of 6 months are especially vulnerable for complications due to influenza
Prime/boost immunization trends towards higher titers in dams than prime only. This trend of influenza-specific maternal antibodies can been seen in the pups, when dams received multiple immunizations as compared to a single immunization (Fig. 1b, no formal statistical analysis was performed on these data)
Even more interesting was the observation that three vaccinations of mothers during pregnancy was able to confer protection against lethal influenza virus challenge to all offspring compared to mock immunization (p < 0.001), see Fig. 4b. These results indicate that multiple immunizations of mothers prior to delivery correlate to the level of homologous antibodies found in the offspring and to passive protection transferred against lethal influenza challenge
Summary
Various studies have shown that infants under the age of 6 months are especially vulnerable for complications due to influenza. Previous influenza pandemics including the recent 2009 swine flu pandemic have shown that pregnant women and young children under 6 years of age are at increased risk of complications from influenza infection [1,2,3,4]. The CDC Advisory Committee on Immunization Practices (ACIP) recommended vaccination against influenza for this vulnerable group since 2003, irrespective of the trimester of the pregnancy. A number of countries, including the USA [11], recommends to vaccinate all children between 6 months and 5 years of age. While vaccination is the main preventative countermeasure against influenza, there are currently no vaccines licensed for use in this vulnerable group of infants
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