Vaccine-preventable disease incidence of pneumococcal conjugate vaccine in the Finnish invasive pneumococcal disease vaccine trial

Estimation of the full disease burden caused by Streptococcus pneumoniae is challenging due to the difficulties in assigning the aetiology especially in lower and upper respiratory infections. We estimated the pneumococcal disease burden by using the vaccine-preventable disease incidence (VPDI) of PHiD-CV10 vaccine (GSK) in our clinical trial setting. Finnish Invasive Pneumococcal disease (FinIP) trial was a cluster-randomized, double-blind trial in children <19 months who received PHiD-CV10 in 52 clusters or hepatitis B/A vaccine as control in 26 clusters according to 3+1 or 2+1 schedules (infants < 7 months) or catch-up schedules (children 7-18 months). Outcome data were collected using Finnish routine health-care registers, consisting of THL National Infectious Diseases Register, THL Care register, and Benefits Register of Social Insurance Institution of Finland. Blinded follow-up lasted from the date of first vaccination (trial enrolment Feb-2009 through Aug-2010) to January 31, 2012 for Invasive Pneumococcal Disease (IPD) and to end of December 2011 for four other outcomes: non-laboratory-confirmed IPD, hospital-diagnosed pneumonia, tympanostomy tube placements, and antimicrobial purchases. VPDI was estimated as difference in disease incidences between PHiD-CV10 clusters and control clusters. Altogether >47,000 children were enrolled. In 30,527 vaccinated infants <7 months at first dose, the VPDIs per 100,000 person-years were 75 for laboratory-confirmed IPD, 210 for non-laboratory-confirmed IPD, 271 for hospital-diagnosed pneumonia, 1143 for any tympanostomy tube placements and 11,381 for antimicrobial outpatient prescription, mainly due to otitis media. In a European developed-country setting, over 95% of the disease episode reductions in vaccinated children were seen in mild upper respiratory infections. The VPDIs of severe diseases are underestimated, because the majority of invasive disease goes undetected with routine blood-culture-based definitions. Evaluation of the absolute reduction achievable with vaccinations using sensitive case detection is essential for understanding the full disease burden, for valid cost-effectiveness analyses and for appropriate vaccination policy decisions. Registration: ClinicalTrials.gov, NCT00861380 and NCT00839254 .