Impact of 13-valent pneumococcal conjugate vaccination introduction in children on pneumonia hospitalizations among adults aged 65 or more in Portugal

Background The incidence of pneumonia and pneumonia related hospitalizations still increasing in different European and American Countries. However, in western countries this increase is driven by secondary diagnoses, recurrent pneumonia episodes in elderly and among those with comorbidities. Given the high frequency of Streptococcus pneumoniae among all pneumonia, it is reasonable to expect that a wide use of pneumococcal vaccines would reduce the burden of pneumonia in the elderly due to a direct and indirect effect. In Portugal, pneumococcal vaccines are available since 1996: pneumococcal polysaccharide vaccine (PPSV23) in 1996; heptavalent conjugated pneumococcal vaccines (PCV7) in 2001; PCV10 in April 2009 and PCV13 in January 2010. PPSV23 and PCV13 are widely recommended for risk groups and elderly. PCV7 serotypes reduced from 31% in 1999–2003 to 11% in 2009–2011 in non-invasive pneumococcal pneumonia (PP), but no decreasing trend was observed for PCV13 and PPSV23 serotypes until 2011. Trends in pneumococcal pneumonia after PCV13 introduction are not known in Portugal. Thus, this study aims to assess population level impact of infant PCV13 introduction on burden of pneumonia among adults aged 65 or more in Portugal through comparison of trends in PP hospitalization rates before and after PCV13 introduction. Methods We performed an ecological study using hospital discharge registry data. Pneumococcal Pneumonia was defined as having a principal diagnosis coded as 481 (International Classification for Diseases - 9th version). To assess trends in hospitalization rates before (July 2003–June 2009) and after (July 2010–June 2016) PCV13 introduction interrupted time series analysis was used. Annual average change of pneumonia hospitalization rates was estimated by Poisson regression models adjusted for seasonality and allowing for over-depression. PP hospitalization rates estimated after immunization program introduction were compared with those projected based on pre-vaccination period trend. Bacterial pneumonia caused by pathogens other than S. pneumoniae was used for sensitivity analysis. Results At baseline, the overall PP hospitalization rate was 10.2/10 4 . The rates varied markedly by age group, the highest baseline rates were observed among those aged 85 years or more, 38.6/10 4 in males and 23.4/10 4 in females. Statistically significant decline in overall PP hospitalization rate was verified during pre-PCV13 period, the rate decreased on average by 4.6% per year (IRR = 0.954; 95% CI: 0.943 to 0.964). The decreasing trend continued after PCV13 introduction, with more pronounced decline of 12.8% (IRR = 0.872; 95% CI: 0.858 to 0.886) per year. The decrease in PP hospitalizations was significant in all subgroups, the largest decline in both pre-PCV13 (5.8% per year) and PCV13 (14.3% per year) periods was verified for males aged 75–84. Smaller decrease was observed for Bacterial pneumonia after 2010 (IRR = 0.915; 95% CI: 0.913 to 0.937). Conclusions Using population-based nationwide registry data, we found considerable decrease in hospitalizations’ rates for PP in adults aged 65 or more years following infant PCV13 introduction in Portugal. Given the ecological design, we cannot exclude the effect of factors other than vaccination, namely changes in diagnosis and coding practices or the reduction of other pneumonia risk factors as tobacco, since decreasing trend was also observed for bacterial pneumonia after 2010.