Changes in serotypes causing invasive pneumococcal disease (2005-2007 vs. 1997-1999) in children under 2 years of age in a population with intermediate coverage of the 7-valent pneumococcal conjugated vaccine.

Serotypes causing invasive pneumococcal disease (IPD) in children aged <2 years in Catalonia (Spain) before and after licensing of the 7-valent pneumococcal conjugated vaccine (7vPCV) were assessed, using samples taken during 1997-1999 and 2005-2007 respectively. The distribution of serotypes causing IPD within these groups was obtained by serotyping strains sent by 22 Catalan hospitals to the Carlos III Health Institute, Madrid. Between 1997-99 and 2005-2007, the proportion of vaccine serotypes causing IPD in Catalonia fell from 70.54% to 31.67% (p <0.0001). The proportion of vaccine-related serotypes, mainly serotype 19A, increased from 9.82% to 32.50% (p <0.0001). The proportion of non-vaccine, non-related serotypes (serotypes not related to vaccine serotypes) rose from 19.64% to 35.83% (p <0.05). Within this group, the proportions of serotype 24F increased significantly. There has been a change in the distribution of serotypes isolated from cases of IPD in children <2 years old in Catalonia, comprising a reduction in the proportion of 7-valent vaccine serotypes, a rise in vaccine-related serotypes, especially 19A, and a smaller rise in non-vaccine, non-related serotypes, especially serotype 24F. A new 13-valent vaccine will cover 77.91% of the serotypes causing IPD in children <2 years old in Catalonia from 2005 to 2007.