BOSTON, MARCH 22, 2026 —
Key Takeaways
- Scientists at the University of Louvain identified a naturally occurring bacterium called Dolosigranulum pigrum living in the respiratory tract that appears to significantly reduce the risk of developing long COVID
- People with higher levels of this bacterium were far less likely to develop persistent long COVID symptoms — including crushing fatigue, brain fog, and shortness of breath — after infection
- The discovery opens the door to a potential nasal spray probiotic that could be taken before winter to protect against both long COVID and severe influenza
More than 10 million Americans are currently living with long COVID. They did not ask for it. They cannot predict when it will end. And for years, medicine had almost nothing to offer them — no reliable biomarker, no proven treatment, no clear explanation for why some people recover fully while others spend months unable to get off the couch.
A study published this week in the peer-reviewed journal Microbiology Spectrum may have just changed that. After five years of research, scientists in Belgium have identified a specific bacterium living naturally in the human respiratory tract that appears to play a powerful protective role against long COVID. It does not come from a drug. It does not require a prescription. It is already living inside some people’s noses right now — and its presence, or absence, may be quietly determining who gets long COVID and who does not.
What the Research Found
The study was launched in 2021, at the height of the COVID-19 pandemic, by researchers at the University of Louvain and its affiliated hospital, the Cliniques universitaires Saint-Luc in Belgium. Their goal was straightforward: could they identify, during the acute phase of a COVID-19 infection, which patients were most likely to go on to develop long COVID?
After tracking 156 patients and analyzing their blood samples and nasopharyngeal swabs — the same type of swab used in a standard COVID test — for molecular signatures linked to persistent disease, the team zeroed in on a single bacterium: Dolosigranulum pigrum.
The finding was clear. Patients with higher levels of Dolosigranulum pigrum in their respiratory tract during the acute phase of infection were significantly less likely to develop the long COVID symptoms that the study focused on: severe fatigue, cognitive problems, and respiratory issues including shortness of breath. Patients with lower levels of the bacterium showed a significantly greater tendency to develop persistent, debilitating symptoms.
The research team described the bacterium as part of the respiratory microbiome — the community of microorganisms that naturally live in the airways, just as the gut microbiome lives in the digestive tract. And just like the gut, the balance of that respiratory community appears to matter enormously for long-term health.
Why This Bacterium — and Why Now
Dolosigranulum pigrum is not a new discovery. Scientists had already identified its protective role against severe influenza in earlier research. What makes this week’s study significant is that it extends that protection to long COVID — a completely different disease with a completely different mechanism — suggesting the bacterium may play a broader role in helping the body regulate its immune response to serious respiratory infections.
The research team believes the bacterium works by influencing how the immune system behaves in the aftermath of a viral infection. Long COVID is not simply a case of the virus lingering indefinitely. It involves a complex, poorly understood interaction between viral persistence, immune dysregulation, and chronic inflammation. Researchers at UC San Francisco confirmed earlier this year that SARS-CoV-2 can persist for months in tissues across the body — the lungs, brain, liver, heart, and gut — driving ongoing inflammation long after the acute infection ends.
The Belgian team’s findings suggest that Dolosigranulum pigrum may help regulate that inflammatory response — keeping the immune system from the kind of prolonged overactivation that appears to drive long COVID’s most debilitating symptoms.
Long COVID — Who It Affects and What It Costs
Long COVID at a Glance — 2026
| Metric | Figure |
|---|---|
| Americans with long COVID | 10+ million |
| Global long COVID cases | ~400 million |
| Share of COVID patients who develop it | ~6% worldwide |
| Most common symptoms | Fatigue, brain fog, shortness of breath |
| Average duration of symptoms | Months to years |
| Annual economic cost to U.S. | Estimated $3.7 billion in lost productivity |
| Current FDA-approved treatments | Zero |
What Comes Next — A Nasal Spray That Prevents Long COVID?
The most exciting implication of this research is what it points toward. If Dolosigranulum pigrum can be shown to actively protect against long COVID — not just correlate with better outcomes — then the path toward a practical intervention becomes clear. The research team itself has flagged the possibility of developing a probiotic nasal spray containing the bacterium, designed to be taken before the winter respiratory season to boost natural protection against both long COVID and severe influenza.
The concept is not as far-fetched as it sounds. Probiotic interventions for the gut microbiome are already commercially available and widely studied. A respiratory microbiome equivalent — delivered directly to the nose where the bacterium naturally lives — would require rigorous clinical trials to confirm safety and efficacy, but the biological rationale is now established.
The study also produced a secondary finding with immediate practical implications. Non-targeted broad-spectrum antibiotics — the kind prescribed for a wide range of infections, often without a specific bacterial diagnosis — were found to disrupt the respiratory microbiome in ways that reduced the presence of protective bacteria like Dolosigranulum pigrum. In plain terms: overuse of antibiotics may be quietly depleting the very microbes that protect against long COVID.
That single finding reframes something millions of Americans do every winter without a second thought. Taking antibiotics for a respiratory illness they do not technically need — a viral infection that antibiotics cannot treat — may be removing a layer of natural protection that the body depends on.
The research does not yet tell doctors how to restore Dolosigranulum pigrum once it is depleted, or whether a future nasal spray will work the way early results suggest. But for the 10 million Americans still waking up exhausted, still struggling to think clearly months after their COVID infection ended, and still waiting for medicine to offer them anything concrete — this week’s discovery is the most specific biological lead the field has produced in years. And it was living in someone’s nose the whole time.
