Does a Decrease in Bifidobacterium Harm Health? Exploring Dr. Sabine Hazan’s Claims

Introduction

The human gut is home to trillions of microbes that play crucial roles in digestion, immunity, and even brain health. Among these, Bifidobacterium is one of the most studied and respected “friendly bacteria.” Recently, some researchers, including gastroenterologist Dr. Sabine Hazan, have raised concerns that COVID-19 infection—and possibly mRNA vaccination—may reduce levels of Bifidobacterium. She argues that this decline may be linked to a variety of diseases, ranging from severe viral illness to autoimmune disorders.

What is Bifidobacterium?

Bifidobacterium is a genus of anaerobic, Gram-positive bacteria that colonizes the intestines, particularly in infants and healthy adults. They help maintain gut balance, ferment fibers into short-chain fatty acids (SCFAs) like acetate and lactate, and support immune function (O’Callaghan & van Sinderen, 2016). High levels of Bifidobacterium are generally considered a marker of gut health.

Dr. Sabine Hazan’s Observations

Dr. Hazan, founder of ProgenaBiome, has conducted microbiome research looking at the effects of COVID-19 and vaccination on gut bacteria. In preliminary studies and conference presentations, she suggested:

1. COVID-19 Severity

   • Patients with severe COVID-19 often show low levels of Bifidobacterium compared to those with mild cases (Hazan et al., 2022).

   • She proposed that loss of bifido worsens the risk of a cytokine storm, an immune overreaction linked to organ damage.

2. Vaccine Effects

   • In a poster and preprint, Hazan suggested that mRNA vaccination may also reduce bifidobacteria levels in some individuals (Hazan, 2024).

   • These results have not yet been widely peer-reviewed, but they have generated discussion.

3. Neurological and Developmental Disorders

   • Hazan has connected reduced Bifidobacterium to neurological issues such as autism spectrum disorder (ASD).

   • The rationale: bifido bacteria produce metabolites like GABA and tryptophan derivatives, which influence the gut-brain axis (Cryan et al., 2019).

4. Chronic and Autoimmune Conditions

   • She claims that a loss of bifido could increase risks for:

     • Autoimmune diseases (Crohn’s disease, multiple sclerosis)

     • Allergies and asthma (due to impaired immune tolerance)

     • Metabolic disorders (obesity, type 2 diabetes)

     • Inflammatory bowel disease (IBD)

Biological Mechanisms Behind the Claim

The reasoning behind Hazan’s argument centers on the protective role of Bifidobacterium:

• Immune Regulation: Bifido species help reduce inflammatory cytokines such as TNF-α and IL-6. Low levels may promote uncontrolled inflammation.

• Gut Barrier Integrity: Bifido-derived acetate strengthens intestinal lining; its absence may lead to leaky gut and systemic inflammation.

• Nutrient Production: Bifido synthesizes vitamins (B-group, folate, K). Reduced populations could lead to nutritional deficiencies.

• Gut–Brain Communication: Bifido contributes to neurotransmitter balance, so its reduction may disturb neurological health.

Controversy and Scientific Debate

While Bifidobacterium clearly plays an important role in health, Hazan’s vaccine-related claims remain controversial. Some of her findings are based on small-scale studies, preprints, or conference abstracts that have not undergone extensive peer review. Larger, controlled clinical trials are needed to confirm whether vaccines truly affect bifido levels in a way that causes disease.

It’s also important to note that other factors—diet, antibiotics, age, stress, and illness—can all reduce Bifidobacterium. Therefore, causation versus correlation remains a central debate.

Conclusion

Dr. Sabine Hazan has argued that a decrease in Bifidobacterium may worsen COVID-19 severity, increase the risk of cytokine storms, contribute to neurological issues like autism, and promote autoimmune and metabolic conditions. While her research has brought attention to the critical role of gut microbes in immune health, her most provocative claims—particularly regarding vaccines—require much stronger scientific validation.

What is clear, however, is that supporting gut health through diet, prebiotics, probiotics, and lifestyle may be one of the simplest ways to maintain a resilient immune system.

References (APA Style)

Cryan, J. F., O’Riordan, K. J., Cowan, C. S. M., Sandhu, K. V., Bastiaanssen, T. F., Boehme, M., … & Dinan, T. G. (2019). The microbiota-gut-brain axis. Physiological Reviews, 99(4), 1877–2013. https://doi.org/10.1152/physrev.00018.2018

Hazan, S. (2024). COVID-19 and vaccine effects on the microbiome [Preprint]. Preprints.org. https://www.preprints.org/manuscript/202407.1505/v1

Hazan, S., Stoll, B., & Wainstein, J. (2022). Messenger RNA SARS-CoV-2 vaccines affect the gut microbiome. American Journal of Gastroenterology, 117(10S), S227. https://doi.org/10.14309/01.ajg.0000867975.13534.e2

O’Callaghan, A., & van Sinderen, D. (2016). Bifidobacteria and their role as members of the human gut microbiota. Frontiers in Microbiology, 7, 925. https://doi.org/10.3389/fmicb.2016.00925