Impact of pneumococcal vaccination in Denmark during the first 3 years after PCV introduction in the childhood immunization programme.

BACKGROUND AND AIMS: The 7-valent pneumococcal conjugate vaccine (PCV7) was introduced in Denmark in October 2007 in a 2+1 schedule with a catch-up programme for children up to 17 months of age. To assess the impact of PCV we evaluated on the whole population: (1) direct and indirect effects on incidence of invasive pneumococcal disease (IPD), (2) changes in pneumococcal serotype distribution and (3) IPD related mortality.

METHODS: We compared disease incidence in pre-PCV (years 2000-2007) and PCV periods (years 2008-2010) based on national surveillance data.

RESULTS: In children aged 0-5 years the overall incidence of IPD decreased from 26.7 to 16.3 cases per 100,000 (IRR 0.58; 95% Confidence Interval (CI) [0.48-0.69]) and case fatality declined from 1.8% (12 deaths) in the eight-year pre-PCV period to 0% (no deaths) in the three-year PCV period. In the whole population the overall incidence of IPD and of IPD caused by vaccine serotypes declined significantly from 19.5 to 17.7 and from 7.7 to 3.8 cases per 100,000 persons comparing the two periods. The incidence of IPD due to non-vaccine serotypes (NVT-IPD) increased significantly from 11.8 to 13.9 cases per 100,000 in the whole population (incidence rate ratio 1.18; 95% CI [1.12-1.24]) with predominance of the serotypes 1.7F and 19A.

CONCLUSIONS: We report a marked decline in incidence in IPD in both vaccinated and non-vaccinated age groups and a minor but statistically significant increase in incidence of IPD due to NVTs in both vaccinated and non-vaccinated groups with predominance of serotypes covered by higher valence pneumococcal conjugate vaccines.