The effect of polyvalent pneumococcal polysaccharide vaccine on nasopharyngeal and nasal carriage of Streptococcus pneumoniae.

To investigate the possible effect of a polyvalent pneumococcal vaccine on the nasopharyngeal and nasal carriage of Streptococcus pneumoniae, we studied 313 children under 8 years of age who had received either 14-valent pneumococcal capsular polysaccharide vaccine (Pn) or Haemophilus influenzae type b capsular polysaccharide vaccine (Hib) after having recovered from acute otitis media. Nasopharyngeal and nasal swabs were obtained during a symptomless phase, 6 to 12 months after the vaccination, and cultured by routine bacteriological methods. All S. pneumoniae strains were serotyped and among H. influenzae strains, type b was identified. In the group that had received the Pn vaccine, the carriage rate of S. pneumoniae types present in the vaccine (type 6 excluded) was 20%, somewhat but not significantly lower than the 30% carriage in the group having received the Hib vaccine. Conversely, the carriage rate of H. influenzae was slightly higher in the Pn (26%) than in the Hib (19%) vaccine group. 14% of the H. influenzae strains were of type b, and this proportion was the same in both vaccine groups. There were no differences between the two vaccination groups in the carriage rates of other S. pneumoniae types or of Staphylococcus aureus or of group A hemolytic streptococci. S. pneumoniae was more often cultured from nasopharyngeal than nasal swabs, especially in children over 6 years, whereas the total carriage rates of S. pneumoniae and H. influenzae were largely unaffected by age.