Abstract
Despite significant advances in child survival in the last few decades, infectious diseases continue to be one of the main causes of morbidity and mortality, especially in the neonatal period. Newborns are at increased risk of infections because their dynamic developing immune system is not always able to mount an efficient protective immune response against pathogens.
Vaccination remains one of the most cost-effective ways of preventing infection. Extended vaccination programs worldwide (WHO) have significantly improved child survival by preventing infections such as polio, pertussis, smallpox, and measles. However, when it comes to neonatal immunization, there are just a few vaccines licensed for administration in the first days of life including vaccination against tuberculosis, hepatitis B, and polio.
Several factors might affect the insufficient contribution of vaccines to mortality reduction in neonates. First, programming of the immune system in early life and immune response might differ both at neonatal and later age. The neonatal immune response is characterized by high reliance on innate immune mechanisms, since the child’s adaptive immune response requires time to organize its architecture and generate protective immunity. There is still scarce knowledge and awareness of risks and benefits of neonatal immunization. Finally, current vaccines administered to neonates do not specifically target the pathogens that cause severe infection in the first weeks of life such as Group B Streptococcus, Klebsiella species, Staphylococcus aureus, Escherichia coli, Respiratory Syncytial Virus. Interestingly, epidemiologic studies have linked early life BCG immunization to an unanticipated reduction (50%) in all cause mortality, which greatly exceeds a reduction in mortality attributable to TB. These observations suggest that BCG induces heterologous protection against antigenically diverse, unrelated pathogens. One of the suggested mechanisms for heterologous protection against infection in the context of BCG vaccination is innate immune memory, also known as “trained immunity”.
A natural tool to protect the vulnerable infants until their immune system can adequately respond to vaccinations or infections is maternal passive immunization. Maternally derived pathogen-antigen specific antibodies are passively transferred throughout the placenta and later in colostrum and breast milk, ready to be used against infections in early life. The dynamic exchange that takes place at the fetal-maternal interface during intrauterine life and through breastfeeding in post natal life, allows also the transfer of antigen presenting cells and maternal immune cells, probably in order to stimulate the developing fetal immune system in a harmless way. This topic is object of the ongoing research and will extend the impact of maternal immunization to other mechanisms other than passive immunity by itself.
Presented by Dr. Eva Piano Mortari, Bambino Gesù Children’s Hospital, Rome, Italy
Chaired by Michela Ciocca, DISCAB, UNIVAQ
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