[Immunogenicity of hepatitis B vaccination in preterm infants started soon after birth: the implications for prevention].

Infections by the hepatitis B virus (VHB) that occur during infancy, acquired from a mother carrying the virus, account for 40% of all infections and are of great clinical and epidemiological relevance worldwide. Despite the acute infection being symptomatic in less than 10% of children, the development of a chronic infection and its consequences, after an acute infection, is inversely proportional to age of exposure. The risk of a chronic infection is at a maximum (70-90%) in children who acquire an infection during the perinatal period and it is these children that constitute the main virus reservoir for spreading the infection to other individuals.