Pneumococcal vaccines do not reduce pneumonia hospitalizations in at-risk adults
Community-acquired pneumonia represents a significant burden of morbidity and mortality, particularly among adults with chronic illnesses. Among the responsible agents, the bacterium Streptococcus pneumoniae is the most frequent cause, followed by viruses, whose impact has been better understood since the COVID-19 pandemic. Pneumococcal vaccines, designed to prevent severe forms of the disease, come in two main types: polysaccharide vaccines and conjugate vaccines, which target different strains of this bacterium.
A recent study conducted in Spain between 2020 and 2024 evaluated the effectiveness of these vaccines in adults aged 18 to 64 with risk factors. The researchers compared 805 patients hospitalized for pneumonia with 806 patients hospitalized for other reasons, all of whom had underlying medical conditions. Participants were classified according to their vaccination status: polysaccharide vaccine only, conjugate vaccine only, sequential vaccination, or unvaccinated.
The results show that none of the tested vaccination strategies significantly reduced the risk of hospitalization for pneumonia. Among immunocompromised individuals, the polysaccharide vaccine was even associated with negative efficacy—meaning an apparent increase in risk—likely due to confounding bias: the most fragile patients, who are most likely to develop severe forms, are also the ones most often vaccinated.
This lack of protection could be explained by several factors. First, current vaccines do not cover all existing types of pneumococci—more than 100 have been identified to date. Second, the pneumonias included in the study may have been caused by pathogens other than those targeted by the vaccines. Finally, the study period, marked by the COVID-19 pandemic, may have influenced the results, as public health measures such as mask-wearing and social distancing temporarily reduced the circulation of many respiratory viruses.
The researchers emphasize that, despite these disappointing results, vaccination remains an important tool, especially for very high-risk populations. They suggest considering optimized strategies, such as the use of broader-spectrum conjugate vaccines or better-adapted sequential vaccination schedules. However, current data do not confirm a clear benefit for adults under 65 with risk factors.
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Original Publication
DOI: https://doi.org/10.1186/s41479-026-00201-6
Title: A multicentre case-control study about effectiveness of pneumococcal vaccination against pneumonia hospitalization in at-risk adults
Journal: Pneumonia
Publisher: Springer Science and Business Media LLC
Authors: María Liébana; Diana Toledo; Núria Soldevila; María Morales-Suarez-Varela; Concepción Prados-Sánchez; Amelia Fernandez-Sierra; Gemma Navarro; Vicente Martín; Judith Chamorro; Mikel Egurrola; Marta Rodriguez-Suárez; Angela Domínguez; ; María Liébana; Diana Toledo; Núria Soldevila; María Morales-Suarez-Varela; Concepción Prados-Sánchez; Amelia Fernandez-Sierra; Gemma Navarro; Vicente Martín; Judith Chamorro; Mikel Egurrola; Marta Rodriguez-Suárez; Angela Domínguez; Aurea Morillo; Raquel Valencia; Mª Mar Rodríguez; José Antonio Marín; Gerardo Rubiera; Tania Fernández-Villa; Graciela López-Muñiz; Carmen Fernández-Martínez-de-Septien; Silvia Fernández; María Grau; Núria Torner; Carles Vilaplana; Lluís Forcadell; Cristina Rius; Anna Vilella; Silvia Simó-Nebot; Eva del Amo; Magda Campins; Xavier Martínez; José Angel Rodrigo; Judith Martínez; Ramon Boixeda; Julia Jaumandreu; Jenaro Astray; Alberto Mangas-Moro; Juan Carlos Galán; Amaranta McGee-Laso; Laura Moreno-Galarraga; Nerea Díaz-Sánchez; Idaira Fernandez-Rodriguez; Cristina Llonch; Itziar Casado; Fernando Baigorria-Feltrin; Alba Gasque; Sara Marquínez-Noriega; Patricia García; Isabel Peraita-Costa; Francisco Sanz