Serotype epidemiology and case-fatality risk of invasive pneumococcal disease: a nationwide population study from Switzerland, 2012-2022.

In Switzerland, thirteen-valent pneumococcal conjugate vaccine (PCV13) has been introduced in 2011. During the COVID-19 pandemic, cases of invasive pneumococcal disease (IPD) have decreased but consequences on the serotype epidemiology are less clear. The objective of the study has been to analyse the impact of PCV13 introduction and the COVID-19 pandemic on the IPD epidemiology and investigate the changes in the case fatality risk (CFR). We analysed data from the Swiss nationwide surveillance for the period 2012-2022. Poisson and logistic regression analyses were performed allowing us to inspect trends over time and to define serotypes that are associated with case fatality. In total, 8747 IPD cases were included from 2012 to 2022. IPD incidence dropped in the years 2020 (6.0/100,000) and 2021 (5.5/100,000) but recovered in 2022 (9.1/100,000). While the incidence numbers of patients >65 years did not reach the pre-pandemic level, numbers significantly increased in infants <1 year in 2022 (IRR 1.08, 95%CI: 1.01-1.16). The incidence of PCV13 serotypes among all IPD cases decreased until 2019 before increasing again during the pandemic (in 2022). Logistic regression analyses revealed that the PCV20 serotype 11A (OR: 1.76, 95%CI: 1.14-2.64), and the PCV13 serotypes 3 (OR: 1.26, 95% CI: 1.04-1.53) and 19F (OR: 1.76, 95%CI: 1.14-2.65) were significantly associated with increased CFR. In conclusion, the COVID-19 pandemic has had only minor temporary effects on the serotype distribution. Continued use of vaccines with extended serotype coverage may further reduce IPD disease burden and mortality.