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Evolution of Invasive Pneumococcal Disease in Adults in Spain (2009-2024): Impact of Conjugate Vaccines Pcv20 Y Pcv21

Year: 2026

Type: article

Abstract: Streptococcus pneumoniae has a critical relevance in public health due to its ability to cause severe invasive diseases. Conjugate vaccines have been essential to control its impact. The recently implemented PCV-20 and PCV-21 protect against 20 and 21 serotypes, respectively. Besides, the PCV-21 contains serotypes never before included, being also a vaccine mainly directed to adults. However, serotype replacement has emerged with many non-vaccine serotypes showing antibiotic resistance, specially to β-lactams, macrolides and tetracyclines. This study is part of the microbiological surveillance work carried out by the National Microbiology Centre (CNM), where the Pneumococcus Unit acts as the National Reference Laboratory (LNR). Pneumococcus isolates were analysed between 2009 and 2024. Given that these represent approximately 80% of the actual total number of cases, a correction factor was applied to estimate the incidence. The isolates were identified using optochin discs and bile salt solubility tests. Subsequently, antimicrobial sensitivity was evaluated using the disc-plate method, and the minimum inhibitory concentration (MIC) was determined in those isolates that showed resistance. Serotyping was performed by dot-blot. In inconclusive cases, PCR and sequencing of the capsular wzy gene were used. Since the introduction of PCV13 in 2010, PCV20-non-21 serotypes have markedly declined, while PCV21-non-20 serotypes have increased, especially among adults over 65 and 80 years old. During the COVID-19 pandemic, cases sharply declined at all ages due to non-pharmacological measures like masking, isolation, and social distancing. From 2021 onwards, coinciding with the lifting of these measures, is observed a gradual increase and recovery in incidence, reaching pre-pandemic levels in the period 2023-2024. The PCV20-non-21 serotypes showed a heterogeneous distribution, with a few of them causing the most cases. After PCV13 introduction, some, like 1 and 5, declined strongly. Serotype 4 has notably increased, becoming one of the most prevalent after the COVID-19 pandemic, while 9V and 19F remain frequent and with a high antimicrobial resistance. In contrast, serotypes PCV21-non-20 showed a more uniform distribution, although with an increasing incidence in recent years in all age groups. In addition, were analysed the MIC and MIC of serotypes with increasing circulation associated with high antibiotic resistance. Serotypes 9V, 14, and 19F, belonging to PCV20-non-21, showed much higher MIC values and against more antibiotic families, which can be explained by the fact that they have been exposed to a selective pressure by the vaccine. Serotypes 15A, 23B, and 35B, belonging to PCV21-non-20, showed lower MICs and were also susceptible to more antibiotic families, which can be explained by the lack of selective pressure. PCV13 has been shown to be effective in reducing the incidence of ENI caused by vaccine serotypes in adults. A phenomenon of serotype replacement has been identified, with a progressive increase in serotypes not covered by current vaccines. Despite the use of PCV13, vaccine serotype 4 has expanded since the COVID-19 pandemic, and other vaccine serotypes such as 14 or 19F continue to have a significant disease burden. The serotypes included in PCV20-no-21 have a higher level of antibiotic resistance, with higher MIC50 and MIC90 values. The introduction of PCV21 could represent a significant advance in public health, especially in older adults.

Source: Open Respiratory Archives

DOI: 10.1016/j.opresp.2026.100571