Differential effects of pneumococcal vaccines against serotypes 6A and 6C.
BACKGROUND
Because classic pneumococcal serotyping methods cannot distinguish between serotypes 6A and 6C, the effects of pneumococcal vaccines against serotype 6C are unknown. Pneumococcal vaccines contain serotype 6B but not serotypes 6A and 6C.


METHODS
We used a phagocytic killing assay to estimate the immunogenicity of the 7-valent conjugate vaccine (PCV7) in children and the 23-valent polysaccharide vaccine (PPV23) in adults against serotypes 6A and 6C. We evaluated trends in invasive pneumococcal disease (IPD) caused by serotypes 6A and 6C in the United States, using active surveillance.


RESULTS
Serum specimens from PCV7-immunized children had median opsonization indices of 150 and < 20 for serotypes 6A and 6C, respectively. Similarly, only 52% of adults (25 of 48) vaccinated with PPV23 showed opsonic indices of > 20 against serotype 6C. During 1999--2006, the incidence of serotype 6A IPD decreased by 91% (from 4.9 to 0.46 cases per 100,000 persons; P < .05) among individuals aged < 5 years and by 58% (from 0.86 to 0.36 cases per 100,000 persons; P < .05) among those aged > or = 5 years. Although the incidence of 6C IPD showed no consistent trend (range, 0-0.6 cases per 100,000 persons) among individuals aged < 5 years, it increased from 0.25 to 0.62 cases per 100,000 persons (P < .05) among those aged > or = 5 years.


CONCLUSIONS
PCV7 introduction has led to reductions in serotype 6A IPD but not serotype 6C IPD in the United States.
Park
In H
IH
Departments of Pathology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
Moore
Matthew R
MR
Treanor
John J
JJ
Pelton
Stephen I
SI
Pilishvili
Tamara
T
Beall
Bernard
B
Shelly
Mark A
MA
Mahon
Barbara E
BE
Nahm
Moon H
MH
D000368:Aged; D002648:Child; D002675:Child, Preschool; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D010587:Phagocytosis / Q000502:physiology*; D022242:Pneumococcal Vaccines / Q000276:immunology*; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000276:immunology*; D018074:Vaccines, Conjugate / Q000276:immunology
C414006:23-valent pneumococcal capsular polysaccharide vaccine; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate