Effectiveness of the 7-valent pneumococcal conjugate vaccine: A population-based case-control study

Background. The 7-valent pneumococcal conjugate vaccine (PCV7) has shown high efficacy in preventing invasive pneumococcal disease (IPD) caused by vaccine serotypes. We aimed to assess the overall effectiveness of PCV7 against IPD in Navarra, Spain. Methods. All children aged < 5 years who were diagnosed with IPD during the period 2001-2005 (n= 85) and 5 control subjects per case patient (n =425), individually matched by birth date and birth hospital, were analyzed. Vaccination records were obtained from the regional immunization registry. Conditional logistic regression was used to estimate odds ratios. Results. Eighteen case patients (21%) and 114 control subjects (27%) had received >= 1 dose of PCV7. PCV7 serotypes were responsible for 34 (51%) of the cases in unvaccinated children. The overall effectiveness for case prevention was 31% (odds ratio, 0.69; 95% confidence interval, 0.37-1.27). In a separate analysis, vaccination with PCV7 was 88% effective in preventing IPD due to vaccine serotypes (odds ratio, 0.12; 95% confidence interval, 0.02-0.91) and was associated with a higher risk of IPD due to nonvaccine serogroups (odds ratio, 6.16; 95% confidence interval, 1.63-23.3). Conclusions. These data reveal a higher risk of IPD caused by non-PCV7 serogroups among vaccinated children. Consequently, the overall effectiveness of PCV7 for IPD prevention may be greatly reduced.