• Nasopharyngeal bacterial (pneumococcal) colonization at 6 weeks, 6, 12, 18 and 24 months in infants and at 12 and 24 months of family members [ Time Frame: duration of study, 23 months per subject ]
  
• transmission to family members( sib, caregiver) [ Time Frame: at infants age of 12 and 24 months ]
  

• anti-pneumococcal antibody levels at 12 and 24 months of age [ Time Frame: 23 months ]
  
• antibody levels and B-memory cells after vaccination at 24 months [ Time Frame: 23 months ]
  

Two(2 and 4 months) and three vaccinations (2,4 and 11 months) with 7-valent pneumococcal conjugate vaccine Prevnar in infants are presumed to provide about 90% protection against invasive pneumococcal disease (IPD) for vaccine type pneumococci, at least until 18-24 months of age. Licensure of the vaccine however is based on studies with 3 vaccinations before 6 months and a booster vaccination half a year later (3+1 scheme). Cost-effectiveness in national infant vaccination programs (NIPs)is much improved by high herd-immunity effects,as observed in the USA after licensure of Prevnar in 2000, both for IPD and AOM. However, overall pneumococcal carriage reduction (and nasopharyngeal replacement) has not been assessed in studies with reduced doses.

With reduced carriage reduction, effects on respiratory tract infections and herd immunity may be significantly less.

The primary aim of the current study is to compare effect of 2-doses (at ages 2 and 4 months) with a 3-doses scheme(2+1, at 2, 4 and 11 months) on nasopharyngeal pneumococcal carriage and replacement and family transmission(sibs and caregivers), in order to allow modelling for herd-immunity.

The secondary aim is to determine the effect of a reduced doses scheme on serum antipneumococcal antibody levels at the age of 12 and 24 months.

A third aim is to determine antipneumococcal antibody levels and memory B-cell development after booster vaccination at 24 months of age, after 2 or 2+1 doses and compare these with a first vaccination at 24 months of age.

Opportunities are the determination of nasopharyngeal colonizing pneumococci in unvaccinated infants in the Netherlands before implementation of Prevnar in the NIP, evaluation of replacing pneumococci in the nasopharynx after vaccinations and analysis of effects on other colonizing bacteria like H.influenzae, M. catarrhalis and S.aureus. Furthermore, the relation between colonizing pneumococci and serotypes causing IPD in the Netherlands can be evaluated.

Methods : 1000 infants and families will be included in a randomized,controlled study with 3 interventions groups

1. Prevnar at 2 and 4 months
2. Prevnar at 2, 4 and 11 months
3. Prevnar at 24 months (controls)

The children will be followed until 2 years of age with nasopharyngeal swabs for bacterial culture before the first vaccination, at 6, 12, 18 and 24 months of age. One sibling and one parent/caregiver will be swabbed when the infant is 12 and 24 months. Blood for antibody determination will be obtained from 80 children of groups 1 and 2, and from 30 children in the control group. Questionnaires on health and respiratory infections and antibiotic prescription for RTI will be obtained.

At 24 months of age, all children of groups 1 and 2 will be offered a booster vaccination. Antibody levels will be measured before and 4 weeks after this vaccination at 2 years of age in a subset of 80 children per group and compared with 80 children who received a first vaccination at 24 months of age.