Effects of pneumococcal conjugate vaccine 2 years after its introduction, the Netherlands

Abstract

In the Netherlands, the 7-valent pneumococcal conjugate vaccine (PCV-7) was implemented in a 3+1-dose schedule in the national immunization program for infants born after April 1, 2006. To assess the vaccine's effectiveness, we compared disease incidence before and after vaccine implementation (June 2004-June 2006 and June 2006-June 2008, respectively). We serotyped 2,552 invasive pneumococcal isolates from throughout the Netherlands, covering 25% of the country's population. Clinical characteristics were extracted from hospital records. After June 2006, vaccine-serotype invasive pneumococcal disease (IPD) decreased 90% (95% confidence interval [CI] 68%-97%) in children age eligible for PCV-7; simultaneously, however, non-vaccine-serotype IPD increased by 71% (not significant), resulting in a 44% total net IPD reduction (95% CI 7%-66%). IPD rates did not change for other age groups. In the Netherlands, PCV-7 offered high protection against vaccine-serotype IPD in vaccinated children, but increases of non-vaccine-serotype IPD reduced net vaccine benefits.

Figure 1

Incidence of invasive pneumococcal disease in children <2 years of age in the birth group born after April 1, 2006 (age eligible for 7-valent pneumococcal conjugate vaccine [PCV-7]) and children born before April 1, 2006 (age noneligible for PCV-7), in the postimplementation period compared with age-matched children in the preimplementation period, the Netherlands. Incidence per 100,000 children <2 years of age per year; Pre, preimplementation period (June 2004–June 2006); post, postimplementation period (June 2006–June 2008).

Figure 2

Serotype distribution of invasive pneumococcal disease with regard to preimplementation and postimplementation of 7-valent pneumococcal conjugate vaccine (PCV-7); among persons of all ages, the Netherlands. Preimplementation period June 2004–June 2006; postimplementation period June 2006–June 2008; *p<0.05; proportion of serotypes preimplementation vs. postimplementation period. Calculated using Fisher exact test; all p values are 2 sided.

Figure 3

Serotype distribution of invasive pneumococcal disease cases among children born after April 1, 2006 (age eligible for 7-valent pneumococcal conjugate vaccine [PCV-7]) in the postimplementation period compared with age-matched children in the preimplementation period, the Netherlands. Preimplementation period, June 2004–June 2006; postimplementation period, June 2006–June 2008; other serotypes are 15A, 16F, 22F, 3, 33F, 5, and 9N. *p<0.05; preimplementation vs. postimplementation periods. Proportions calculated using Fisher exact test; all p values are 2 sided.

Figure 4

Age group–specific distribution of clinical invasive pneumococcal disease (IPD) syndromes in the preimplementation and postimplementation periods of 7-valent pneumococcal conjugate vaccine (PCV-7), the Netherlands. Incidence is IPD cases per 100,000 persons per year. Pre, preimplementation period (June 2004–June 2006); post, postimplementation period (June 2006–June 2008).

Figure 5

Age group–specific theoretical coverage of pneumococcal conjugate vaccines during the preimplementation and postimplementation periods of 7-valent pneumococcal conjugate vaccine (PCV-7), the Netherlands. IPD, invasive pneumococcal disease; PCV-10/PCV13, additional coverage by PCV-10 and PCV-13; PCV-13, additional coverage by PCV-13 alone; pre, preimplementation period (June 2004–June 2006); post, postimplementation period (June 2006–June 2008).