Young adults at risk of emerging serotype 4 invasive pneumococcal disease vs. other serotypes in Andalusia (Spain), 2022 to 2024: optimising conjugated vaccines strategies

BACKGROUND: In Spain in 2023, most reported cases of invasive pneumococcal disease (IPD) were caused by serotypes 8, 3, 22F, and 4. Almost 70.0% of serotype 4 cases were notified in Andalusia (southern Spain). Our aim was to characterize socio-demographic and clinical factors associated with serotype 4 versus other serotypes, and to describe theoretical coverage of currently approved vaccines. METHODS: We conducted an observational longitudinal study including individuals with confirmed invasive pneumococcal disease (IPD) reported to the Andalusian Epidemiological Surveillance System from 2022, to 2024. Cases with unavailable pneumococcal serotype data were excluded. Descriptive analyses and multivariable logistic regression were performed to assess the characteristics of IPD cases according to serotype (serotype 4 vs. other serotypes), using R software. RESULTS: A total of 1359 IPD patients were analysed. The 3 most frequent serotypes reported were 8 (20.1%), 3 (17.1%), 4 (10.6%). Factors associated with increased odds of serotype 4 were male sex (OR = 2.36, 95%CI: 1.54-3.71); age groups of 45-64 years (OR = 3.58, 95%CI: 2.22-5.97) and 15-44 years (OR = 3.34, 95%CI: 1.92-5.91) compared to age group ≥65 years old; no previous pneumococcal vaccination (OR = 3.77, 95%CI: 2.15-7.07) and pneumonia (OR = 3.08, 95%CI: 2.03-4.80). History of psychoactive drug use (OR = 2.50, 95%CI: 1.04-5.77) was associated with serotype 4. CONCLUSIONS: Social and demographic factors such as younger age, male sex, location, no previous pneumococcal vaccination, toxic habits and pneumonia as clinical form, were associated with emerging serotype 4 IPD. Public health strategies should adapt and reinforce local vaccination programs to prevent and reduce IPD.