Possibility of application of new pneumococcal conjugate vaccines in children in Slovenia.

ABSTRACT

The emergence of pneumococcal strains resistant to penicillin caused a lot of problems in the therapy of invasive diseases, and added new dimensions to the role of immunisation. In addition to the currently available 23-valent pneumococcal polysaccharide vaccine (PPV) and a new 7-valent conjugate vaccine (PCV) (Prevnar, Wyeth Lederle), two new conjugate vaccines-a 9- and a 11-valent-are being developed. So far, the choice of most appropriate vaccines has depended on the established prevalence of serotypes causing invasive diseases and their antibiotic resistance in the Slovene children population. Between 1993 and 2001, 263 invasive pneumococcal strains isolated from children with invasive diseases were typed. During the period 1998-2001, the same 161 invasive strains were tested for their antibiotic sensitivity. Streptococcus pneumoniae was identified as the major cause of invasive bacterial diseases in the Slovene children population, especially in children under 4 years of age. Distribution by age groups showed the highest incidence in children aged 0-1 years. The predominant serotypes in all age groups were serotypes 14, 1, 19F, 23F, 6B, 18C and 6A. The distribution of penicillin-intermediate and penicillin-resistant strains showed the predominance of serotypes 23F, 14 and 19F. As concerns infection with S. pneumoniae serotypes, we have proved that children aged less than 5 years are more likely to be infected with penicillin-nonsusceptible or intermediate susceptible strains than older children. The 7-valent conjugate vaccine covers 74% of invasive strains in toddlers, but is less effective in older children. We can conclude that the 9-valent vaccine formulation is optimal for our country, but further cost-effectiveness analysis must be done for recommendation of wide use. At that moment it is reasonable to use the 7-valent conjugate vaccine for children with chronic cardiovascular, pulmonary, urinary and liver diseases, with asplenia, neoplasmia, diabetes, meningomyelocoele, before or after bone marrow transplantation and in cases of immunodeficiency.