Impact and effectiveness of 23-valent pneumococcal polysaccharide vaccine against invasive pneumococcal disease in the elderly in England and Wales

Abstract

In 2003 the existing 23-valent pneumococcal vaccine (PPV23) programme for high risk groups was extended to include all ≥ 65 year olds in England and Wales, starting with ≥ 80 year olds and moving to 75-79 and 65-74 year olds by 2005. We conducted an ecological study to assess the impact of the extended PPV23 programme on serotype-specific incidence of invasive pneumococcal disease (IPD) and a case-control study to assess vaccine effectiveness (VE) using the national IPD surveillance dataset. Between 1998 and 2006 IPD incidence caused by PPV23 serotypes in the targeted age-groups was unchanged. IPD caused by the serotypes covered by the 7-valent conjugate vaccine (PCV7) introduced for children in 2006 declined in ≥ 65 year olds after 2006 but was offset by an increase in non-PCV7 serotypes. This increase was similar for the additional 16 serotypes covered by PPV23 and the non-PPV23 serotypes. For the VE study, vaccine history was obtained for controls (n=1270) with non-PPV23 IPD diagnosed between November 2003 and December 2010 and a subset of cases (n=1272) matched for age and time period. VE declined from 48% (95% confidence interval; 32-60%) within two years of vaccination to 15% (-3% to 30%) after five years. Although differences in VE by age and having risk conditions were not statistically significant the highest estimates were in the youngest age group (65-74 years) and in those without risk conditions with a VE estimate of 65% (23-84%) within 2 years of vaccination for non-risk 65-74 year olds. VE differed by serotype (p=0.005), from -23% (-85% to 19%) for serotype 3 to 63% (29-81%) for 12F. In conclusion PPV23 was effective, particularly in healthy under 75 year olds, but protection waned after 5 years. There was no discernible impact of PPV23 on IPD incidence or PCV7-induced serotype replacement, consistent with the modest overall effectiveness, the 45% increased coverage over the former risk-based programme and lack of herd immunity from the PPV23 programme. Based on the VE estimates PPV23 was still considered a cost-effective intervention for the low risk elderly.