Nikhil Prasad Fact checked by:Thailand Medical News Team Aug 13, 2026 38 minutes ago
A commonly used mucus-clearing drug could have a potentially broader role against respiratory viral infections. Researchers are proposing that bromhexine hydrochloride may help reduce the severity of COVID-19 and influenza when used prophylactically, while potentially allowing enough viral exposure for the immune system to develop longer-lasting protection.
Bromhexine is being investigated as a potential prophylactic approach that could reduce the clinical impact of
COVID-19 and influenza while preserving immune responses
The new concept centers on bromhexine’s ability to interfere with TMPRSS2, a human protein that SARS-CoV-2 and influenza viruses can exploit when entering respiratory cells. Importantly, the researchers are not claiming that bromhexine completely prevents infection. Instead, they propose that reducing viral entry could limit early viral multiplication and tissue damage.
The research was conducted by Vanyo Mitev from the Research Institute of Innovative Medical Science, Medical University-Sofia, Sofia, Bulgaria, and the Department of Medical Chemistry and Biochemistry, Medical Faculty, Medical University-Sofia, Sofia, Bulgaria.
A Different Approach to Viral Prophylaxis
According to the proposed mechanism, bromhexine inhibits TMPRSS2-dependent viral entry but may not completely block infection because viruses can use alternative entry pathways. The researchers believe this partial restriction could create an unusual balance: less viral replication and disease, but sufficient viral antigens to stimulate adaptive immunity.
They describe this proposed process as Pharmacologically Attenuated Natural Immunization, or PANI. The idea is that controlled exposure could activate B cells and T cells and ultimately generate immune memory while reducing the likelihood of clinically significant illness.
Strong Immune Response Despite Minimal COVID-19 Symptoms
A key observation involved a 72-year-old man who had been taking bromhexine at 8 milligrams twice daily for approximately two weeks before SARS-CoV-2 infection was detected.
His infection was almost clinically silent, with only mild throat irritation. Yet approximately three months later, his anti-spike antibody concentration reached 2,080 BAU/mL. Around nine months after infection, anti-spike IgG remained strongly positive, with a Vircell anti-S IgG ratio of 22.209.
Researchers considered this especially noteworthy because strong antibody reactivity persisted despite the patient's age, when immune responses can sometimes become less robust.
This Thailand
Medical News report also highlights that the researchers interpret the combination of minimal disease and sustained antibodies as supporting their hypothesis that viral entry might have been attenuated without eliminating the antigen exposure required for immune priming.
High-Risk Household Observation
The man's 71-year-old wife, who was also taking bromhexine prophylactically, had several major risk factors
, including COPD, severe underweight, previous pancreatic cancer surgery and heavy smoking.
Despite presumed household exposure, she remained clinically asymptomatic. Around three months later, her anti-spike antibody concentration measured 1,040 BAU/mL, while anti-spike IgG remained detectable approximately nine months later.
However, researchers caution that her previous COVID-19 vaccination means the antibody response cannot conclusively demonstrate a new infection.
Other Observations Strengthen the Hypothesis
The paper also describes elderly individuals with multiple medical conditions, heavy smokers receiving long-term bromhexine and an eight-year-old child receiving seasonal prophylaxis. Across these observations, researchers reported absent or markedly attenuated clinically apparent COVID-19 or influenza.
Previous research from the group also found prophylactic bromhexine use associated with substantially lower reported COVID-19 infection rates, although prospective controlled trials remain necessary to confirm efficacy.
Conclusions
The observations suggest that bromhexine deserves further investigation as a host-directed prophylactic strategy against COVID-19, influenza and potentially other TMPRSS2-dependent respiratory viruses. However, the proposed PANI mechanism remains a hypothesis, and randomized prospective studies measuring viral loads, neutralizing antibodies and cellular immunity are needed before preventive effectiveness can be established.
The study findings were published as a non-peer-reviewed concept paper on Preprints.org and have not yet been published in a peer-reviewed journal.
https://www.preprints.org/manuscript/202608.0777
Read Also:
https://www.thailandmedical.news/articles/coronavirus
https://www.thailandmedical.news/articles/influenza-or-flu
https://www.thailandmedical.news/articles/covid19-drugs
https://www.thailandmedical.news/articles/long-covid 
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