Rapid increase in non-vaccine serotypes causing invasive pneumococcal disease in England and Wales, 2000-17: a prospective national observational cohort study.

Background: Pneumococcal conjugate vaccines (PCVs) have substantially reduced the incidence of invasive pneumococcal disease caused by vaccine serotypes; however, replacement disease with non-PCV serotypes remains a concern. We describe the population effect of the seven-valent and 13-valent PCVs (PCV7 and PCV13) on invasive pneumococcal disease in England and Wales.
Methods: Using national invasive pneumococcal disease surveillance data for 2016/17, we compared incidence rate ratios (IRRs) against pre-PCV13 (2008/09-2009/10) and pre-PCV7 (2000/01-2005/06) baselines. We also estimated the number of invasive pneumococcal disease cases prevented since the introduction of PCVs.
Findings: In 2016/17, overall invasive pneumococcal disease incidence (9·87 cases per 100 000; 5450 cases) across all age groups was 37% lower (IRR 0·63, 95% CI 0·60-0·65) than pre-PCV7 incidence (14·79 per 100 000; 8167 cases) and 7% lower (0·93; 0·89-0·97) than pre-PCV13 incidence (10·13 per 100 000; 5595 cases). By 2016/17, PCV7-type invasive pneumococcal disease incidence across all age groups had decreased by 97% (0·24 per 100 000; 0·03, 0·02-0·04) compared with the pre-PCV7 period, whereas additional PCV13-type invasive pneumococcal disease decreased by 64% (1·66 per 100 000; 0·36, 0·32-0·40) since the introduction of PCV13. Invasive pneumococcal disease incidence due to non-PCV13 serotypes doubled (7·97 per 100 000; 1·97, 1·86-2·09) since the introduction of PCV7, and accelerated since 2013/14-especially serotypes 8, 12F, and 9N, which were responsible for more than 40% of invasive pneumococcal disease cases by 2016/17. Invasive pneumococcal disease incidence in children younger than 5 years remained stable since 2013/14, with nearly all replacement disease occurring in adults. We estimated 38 366 invasive pneumococcal disease cases were prevented in the 11 years since the introduction of PCV7.
Interpretation: Both PCV7 and PCV13 have had a major effect in reducing the burden of invasive pneumococcal disease in England and Wales; however, rapid increases in some non-PCV13 serotypes are compromising the benefits of the programme.
Funding: Public Health England.
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