Pneumococcal serotype epidemiology and resistance after PCV13 replacement with PCV10, Sweden

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.

Respiratory tract (RT) S. pneumoniae isolates (n=1615; 2020-2023) were serotyped, tested for antimicrobial susceptibility and compared with invasive pneumococcal disease (IPD) isolates (n=397) and PCV13-era data (2016-2018).

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.

Serotypes 19A and 3 re-emerged as predominant, indicating the need for continued surveillance. Our study emphasises the risk of rapid serotype resurgence when lower-valency vaccines are reintroduced.