Impact of heptavalent pneumococcal conjugate vaccine on nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae among day-care center attendees in central Greece.

BACKGROUND

In Greece, the heptavalent pneumococcal conjugate vaccine (PCV7) became available in October 2004 and it was incorporated into the national immunization schedule in January 2006.

METHODS

In February 2005, a yearly surveillance of the nasopharyngeal colonization with Streptococcus pneumoniae in children attending day-care centers in Central Greece began.

RESULTS

Between February 2005 and May 2007, nasopharyngeal cultures were obtained from 1829 children aged 13-76 months (median age, 47 months). The proportion of attendees vaccinated with > or =1 doses of PCV7 increased from 13% (2005) to 33% (2006) and to 70% (2007); 98% had been immunized on toddler catch-up schedules. Among vaccinated carriers, the proportion of PCV7 serotypes decreased from 33% (2005) to 29% (2006) and to 8.6% (2007) (chi for trend, P < 0.001), the proportion of PCV7-related serotypes increased from 13% (2005) to 26% (2006) and to 28% (2007) (P = 0.16), whereas the proportion of non-PCV7 serotypes was 48% in 2005, 31% in 2006, and 55% in 2007 (P = 0.17). The proportion of PCV7 serotypes declined also among unvaccinated carriers. The carriage of serotype 19A did not increase. Among vaccinated carriers, the rate of highly penicillin-resistant isolates decreased from year 1 to year 3, respectively, 11%, 7.7%, and 0.6% (P = 0.001), whereas the proportion of penicillin-intermediate pneumococci was 13% in 2005, 23% in 2006, and 26% in 2007 (P = 0.22).

CONCLUSIONS

In Central Greece, widespread PCV vaccination was followed by a significant reduction of carriage of highly penicillin-resistant pneumococci. The frequency of penicillin-intermediate isolates did not change significantly among vaccinated carriers.