Effectiveness of 23-Valent Polysaccharide Pneumococcal Vaccine and Changes in Invasive Pneumococcal Disease Incidence from 2000 to 2017 in Those Aged 65 and Over in England and Wales.

Background: Invasive Pneumococcal Disease (IPD) is a major public health concern. The effectiveness of 23-valent polysaccharide pneumococcal vaccine (PPV23) against IPD in older age-groups is not fully understood. We measured PPV23 effectiveness against IPD and interpreted changes in IPD incidence between 2000 and 2017. Methods: Public Health England conducts enhanced national IPD surveillance in England and Wales. The indirect cohort method was used to estimate PPV23 effectiveness against IPD in individuals aged ≥ 65 years eligible for PPV23 vaccination during 2012-2016. IPD incidence in 2016/17 was compared to rates during 2000-2003, when neither PPV23 nor pneumococcal conjugate vaccines (PCVs) were routinely used in England and Wales. Findings: PPV23 effectiveness, irrespective of time since vaccination, was 27% (95% CI, 17-35) after adjusting for age, co-morbidity and year of infection. Vaccine effectiveness reduced non-significantly (p = 0.13) with time since vaccination, from 41% (95% CI, 23-54) for those vaccinated within two years, to 34% (95% CI, 16-48) for those vaccinated 2-4 years previously, and 23% (95% CI, 12-32) for those vaccinated ≥ 5 years previously. Vaccine effectiveness did not vary significantly by age but was highest in previously healthy individuals (45%; 95%CI, 27-59). IPD incidence for PPV23 serotypes not included in the PCVs did not decrease after routine PPV23 use but increased significantly since PCV introduction in 2006. Interpretation: PPV23 offers moderate short-term protection against IPD in older adults. PPV23 serotypes comprise an increasing proportion of IPD cases in older adults because of serotype replacement following routine PCV use in children. Funding: European Union's Horizon 2020