By Dr Chun Tang — MBChB (Manchester), MRCGP, MBA · Practising NHS & Private GP · Founder, Little Ox

Dr Tang in the Press: Why You Can Catch Norovirus Twice — And What It Tells Us About Gut Immunity

Earlier this year, I was quoted in several national outlets — including KentOnline, Surrey Live and The Portugal News — on one of the questions I was getting most frequently from patients: why are people getting norovirus again when they already had it this winter?

The answer is important, and it connects directly to something I think about a lot in the context of healthy ageing and supplementation: the relationship between your gut microbiome and your immune system.

What I Said in the Press

My core explanation was this: norovirus doesn't give you long-term immunity. Unlike some viruses where one infection provides lasting protection, norovirus immunity is short-lived — typically lasting only months — and it's strain-specific. The GII.4 and GII.17 strains circulating this season behave differently enough to each other that immunity to one doesn't reliably protect you against the other.

As I explained to KentOnline: the virus spreads through tiny particles in vomit and stool that can linger on surfaces, and you only need a very small number of viral particles to become infected. This is why outbreaks move so fast in shared spaces — schools, offices, care homes.

The practical advice I gave: wash hands with soap and water (alcohol hand sanitisers do not kill norovirus), stay home for at least 48 hours after symptoms resolve, and — critically — stay hydrated. Dehydration is the real danger, particularly for young children and older adults.

What This Tells Us About Gut Immunity

The reason I find norovirus clinically interesting beyond the immediate illness is what it reveals about the relationship between your gut microbiome and immune resilience. Roughly 70–80% of your immune system resides in your gut — in the gut-associated lymphoid tissue (GALT) that lines your digestive tract. A diverse, healthy microbiome actively trains your immune system, regulates inflammatory responses, and produces antimicrobial compounds that help resist pathogens.

When microbiome diversity is low — as it commonly is in adults over 50, in people who've had recent courses of antibiotics, or in those with poor dietary fibre intake — immune responses can be blunted. You're not just more vulnerable to infections like norovirus; your recovery takes longer and the inflammatory aftermath can be more pronounced.

What I Recommend for Year-Round Gut and Immune Support

The two things I consistently recommend to patients who want to support gut immunity are:

1. A high-quality, high-diversity live culture. Not all live cultures are created equal. Single-strain products do little for microbiome diversity. Our Bio Cultures Complex delivers 75 billion CFU across 25 strains, with FOS and inulin prebiotics to sustain the bacteria being introduced. This is the standard I apply when recommending live cultures to my own patients.

2. NAD+ restoration via NMN. The connection between NAD+ and immune function is underappreciated. NAD+ is essential for the function of immune cells including T-cells and macrophages, and NAD+ depletion — which accelerates after 40 — impairs the speed and effectiveness of immune responses. Restoring NAD+ via NMN Pure supports immune cell function at the cellular level, alongside the energy and metabolic benefits it's better known for.

The gut-immune axis is one of the most important and most neglected areas of preventative health. If you're finding yourself repeatedly unwell, or recovering more slowly than you used to, it's worth looking at gut health first.

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