Scientists Identify “Good” Bacteria That May Prevent Long COVID

A small microbe in the respiratory tract may hold important clues about why long COVID persists.

According to the WHO, about 6% of people worldwide who get COVID-19, roughly 400 million people, later develop a long-lasting form of the illness. That shows the condition remains a significant public health challenge.

In 2021, during the COVID-19 pandemic, the University of Louvain (UCLouvain, Belgium) and its hospital, the Cliniques universitaires Saint-Luc, launched a large-scale study to see whether long-term symptoms could be predicted during the acute phase of infection. The goal was to better understand the biological mechanisms involved and potentially identify a preventive treatment.

A Bacterium Linked to Recovery

After five years of research, scientists identified an important role for Dolosigranulum pigrum, a bacterium that naturally lives in the respiratory microbiome. Higher levels of this bacterium were associated with a lower likelihood that long Covid symptoms would persist.

Jean Cyr Yombi, Leïla Belkir, and Julien De Greef, UCLouvain professors and infectious disease specialists at the Cliniques universitaires Saint-Luc, examined the severity of long Covid symptoms in 156 patients. They focused mainly on severe fatigue, cognitive problems, and respiratory issues (shortness of breath).

Laure Elens and Patrice Cani, also UCLouvain professors, along with Bradley Ward, a postdoctoral researcher at the UCLouvain Louvain Drug Research Institute, then analyzed blood samples and nasopharyngeal swabs for molecular signatures linked to this more severe form of the disease. These signatures may help explain why symptoms persist in some patients but not in others.

Clues From the Respiratory Microbiome

UCLouvain and Cliniques universitaires Saint-Luc researchers stated, “This study suggests that certain so-called protective bacteria in the respiratory microbiome may be associated with improved recovery following viral respiratory infections (such as long Covid or influenza), and that their alteration (particularly in the context of severe infection or non-targeted antibiotic therapy) may influence longer-term clinical outcomes.”

In simpler terms, when this bacterium is present in higher amounts, it appears to help protect against long Covid or severe influenza (through a mechanism that has yet to be elucidated). When it is present at low levels, researchers found a greater tendency toward developing a persistent form of the disease.

Implications for Future Treatments

Researchers already knew this bacterium had a protective effect in infectious influenza. The new findings, published in Microbiology Spectrum, add to the evidence that Dolosigranulum pigrum may be beneficial.

Scientists hope the discovery will speed up research and support new treatment strategies, including the possible development of a probiotic, for example, in the form of a nasal spray, that could be used before winter to help protect people from severe infectious diseases such as Covid-19 or influenza.

The study also found that non-targeted antibiotics can affect the respiratory microbiome’s ability to defend against severe infections. That is another reason careful antibiotic use remains important.

Reference: “Association of nasopharyngeal Dolosigranulum pigrum and Corynebacterium species with post-acute sequelae of SARS-CoV-2 in a longitudinal cohort” by Bradley Ward, Laure B. Bindels, Jean-Luc Balligand, Bertrand Bearzatto, Guido Bommer, Patrice D. Cani, Julien De Greef, Joseph P. Dewulf, Laurent Gatto, Vincent Haufroid, Sébastien Jodogne, Benoît Kabamba, Sébastien Pyr dit Ruys, Didier Vertommen, Jean Cyr Yombi, Leïla Belkhir and Laure Elens, 17 March 2026, Microbiology Spectrum.
DOI: 10.1128/spectrum.02313-25

This research involved the University of Louvain HYGIEIA consortium and the Cliniques universitaires Saint-Luc, and was made possible thanks to the support of the Sofina Covid Solidarity Fund and partnerships with the Fondation Saint-Luc, the FNRS (via an emergency research grant) and the WEL Research Institute of the Walloon Region.

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