Pneumococcal vaccination in older adults in the era of childhood vaccination: Public health insights from a Norwegian statistical prediction study.

Two different vaccines, a 23-valent polysaccharide vaccine (PPV23) and a 13-valent conjugate vaccine (PCV13), are available for prevention of invasive pneumococcal disease (IPD) in the population aged 65 years and older (65+). The IPD epidemiology in the 65+ is undergoing change due to indirect effects of childhood immunisation. Vaccine recommendations for the 65+ must take into account these trends in epidemiology. We therefore explored the preventive potential of vaccination strategies to prevent IPD in the 65+, including PPV23, PCV13 or PCV13 + PPV23 in 2014-2019. Quasi-Poisson regression models were fitted to 2004-2014 population-wide surveillance data and used to predict incidences for vaccine-type and non-vaccine type IPD. We determined the number of people needed to be vaccinated to prevent one case per season (NNV) for each strategy and estimated the public health impact on the IPD case counts from increasing the vaccine uptake to 28-45%. Our results indicate that PCV13-IPD will decrease by 71% from 58 (95% prediction interval 55-61) cases in 2014/15 to 17 (6-52) in 2018/19 and PPV23-IPD by 32% from 168 (162-175) to 115 (49-313) cases. The NNV will increase over time for all strategies because of a decreasing vaccine-type IPD incidence. In 2018/19, the PCV13-NNV will be 5.3 times higher than the PPV23-NNV. Increasing the vaccine uptake will lead to a larger public health impact for all scenarios. Combining PCV13 and PPV23 is most effective, but the additional effect of PCV13 will decrease and is only marginal in 2018/19. Our study demonstrates the importance of increasing PPV23 uptake and of developing vaccines that confer broader immunity.