Objectives: To evaluate the impact of the 2018 switch from PCV13 to PCV10 in Sweden's childhood immunisation programme on the serotype distribution of Streptococcus pneumoniae. J o u r n a l P r e -p r o o fMethods: Respiratory tract (RT) S. pneumoniae isolates (n=1,615; 2020-2023) were serotyped, tested for antimicrobial susceptibility and compared with invasive pneumococcal disease (IPD) isolates (n=397) and PCV13-era data (2016)(2017)(2018).Results: Predominant serotypes were 3 (13%), 19A (11%), 23B (10%), and 11A (7.5%).PCV10 coverage was low (4.1%), but increased with PCV13 (29%), PCV15 (30%), PCV20 (47%) and PCV21 (71%).After reintroduction of PCV10, the proportions of serotypes 3 (8.7% to 13%) and 19A (4.5% to 11%) increased (p<0.001), and an increase in serotype 19A was also observed in IPD (5.6% to 19%, p<0.001).Serotype 8 dominated IPD (21%) but was uncommon in RT isolates (2.8%).Among RT isolates, reduced benzylpenicillin susceptibility was observed in 11%.Resistance was highest to trimethoprim/sulfamethoxazole (13%), followed by erythromycin (9.3%), tetracycline (8.5%), and clindamycin (6.9%).Multidrug-and extensively drug-resistant isolates were uncommon (7.9% and 1.1%) and were predominantly serotypes 15A and 19A.Conclusions: Serotypes 19A and 3 re-emerged as predominant, indicating the need for continued surveillance.Our study emphasises the risk of rapid serotype resurgence when lowervalency vaccines are reintroduced.
Yamba et al. (2026) studied this question.