A new study has identified a naturally occurring nasal bacterium that appears to protect people from developing Long COVID — and researchers believe it could be harnessed as a probiotic nasal spray to shield people before they're ever exposed.
The research, published in Microbiology Spectrum in March 2026 by scientists from the University of Louvain (UCLouvain) and Cliniques universitaires Saint-Luc in Belgium, found that patients with higher levels of Dolosigranulum pigrum in their respiratory microbiome were significantly less likely to develop persistent Long COVID symptoms.
What Is Dolosigranulum pigrum?
Dolosigranulum pigrum is a bacterium that naturally inhabits the upper respiratory tract of some people. It is considered a commensal organism — part of the healthy microbiome — and has previously been associated with protection against respiratory infections in children.
The UCLouvain team analysed 156 COVID-19 patients and found a strong correlation: those with higher nasal levels of D. pigrum reported significantly fewer and less severe Long COVID symptoms, including fatigue, cognitive difficulties ("brain fog"), and ongoing respiratory problems.
The Long COVID Problem
Long COVID — also known as Post-Acute Sequelae of SARS-CoV-2 (PASC) — affects an estimated 65 million people worldwide, with symptoms including debilitating fatigue, cognitive impairment, breathlessness, and pain that can persist for months or years after infection.
Despite the scale of the problem, effective preventive or therapeutic strategies remain limited. This discovery provides one of the first biological explanations for why some people develop Long COVID while others recover fully.
Toward a Nasal Spray
The researchers hope the findings will accelerate development of a probiotic nasal spray containing Dolosigranulum pigrum. Such a spray could potentially be used seasonally — before winter respiratory infection periods — to restore healthy mucosal microbiome balance and reduce the risk of severe or persistent outcomes from COVID-19, influenza, and other respiratory viruses.
"Our findings provide a strong rationale for developing targeted respiratory probiotics," the team stated. The study is registered at ClinicalTrials.gov (NCT05557539).
While the current research is observational — meaning it shows correlation but not yet proven causation — the findings open a promising new avenue for prevention that is inherently low-risk, low-cost, and potentially applicable at scale.
Source: Microbiology Spectrum, UCLouvain / Cliniques universitaires Saint-Luc, March 2026
