Am I still immune to norovirus after having it two years ago, given my current exposure to a relative with the infection and my frequent handwashing and other hygiene practices?

Norovirus Immunity After Two Years

You are NOT immune to norovirus two years after your previous infection, and your hygiene practices alone—especially without soap in your bathroom—are insufficient to protect you from this highly contagious virus. 1

Why You're Still Vulnerable

Short-Lived Immunity

• Immunity to norovirus lasts only 8 weeks to 6 months maximum, even against the exact same strain you had before. 1
• After two years, any protective antibodies from your previous infection have long since waned, leaving you fully susceptible to reinfection. 1
• Even worse, you can get infected with different norovirus strains (heterologous strains) regardless of your previous infection history. 1

Viral Evolution Outpaces Immunity

• New norovirus variants (particularly GII.4 strains) continuously emerge and actively evade whatever immunity the population has built up. 1
• The strain your friend has now is almost certainly different from what you had two years ago, meaning your previous infection provides essentially zero protection. 1

Your Current Hygiene Strategy Has Critical Gaps

The Soap Problem is Serious

• Handwashing with soap and running water for at least 20 seconds is the ONLY truly effective method to reduce norovirus contamination on hands. 1, 2, 3
• Without soap, you're relying solely on mechanical removal, which is dramatically less effective against this virus. 1
• Not touching your face is good practice, but it's an unrealistic long-term strategy—people touch their faces unconsciously hundreds of times per day, and one slip-up is all it takes. 1

Why This Virus is So Dangerous

• Norovirus requires as few as 18 viral particles to cause infection—meaning approximately 5 billion infectious doses exist in each gram of an infected person's feces during peak shedding. 1
• The virus spreads through multiple routes: direct person-to-person contact, aerosolized vomit particles, and contaminated surfaces (fomites). 1
• Your friend is shedding massive amounts of virus right now (peak shedding occurs 2-5 days after infection), and will continue shedding for an average of 4 weeks, though at lower levels. 1, 3

What You Must Do Immediately

Fix Your Handwashing Situation

• Get soap for your bathroom TODAY—this is non-negotiable for norovirus prevention. 1, 2
• Wash hands with soap and running water for a full 20 seconds after any potential exposure, before eating, and after using the bathroom. 1, 3
• Alcohol-based hand sanitizers have limited to no efficacy against norovirus and should never replace proper handwashing. 1, 4

Minimize Exposure to Your Friend

• Avoid close contact with your friend until they've been symptom-free for at least 48-72 hours. 2, 3
• Remember that up to 30% of norovirus infections are asymptomatic, so your friend may still be contagious even after feeling better. 1
• If you share living spaces, disinfect high-touch surfaces with chlorine bleach solution (1,000-5,000 ppm), as standard cleaners won't kill norovirus. 4

The Reality Check

Attack Rates Tell the Story

• Even in outbreak settings with infection control measures, attack rates rarely exceed 50%, meaning you have roughly a coin-flip chance of getting infected with significant exposure. 1
• This 50% ceiling exists because of a combination of innate genetic resistance (secretor status), acquired immunity, and asymptomatic infections—but after two years, you only have potential genetic resistance working in your favor. 1

Your Genetic Lottery Ticket

• About 20% of people have a genetic mutation (FUT2 gene) that makes them "non-secretors" who are naturally resistant to many norovirus strains. 1
• If you've only had norovirus once in your life despite multiple exposures, you might be a non-secretor—but this isn't guaranteed protection against all strains. 1
• If you're a "secretor" (the other 80% of people), you're fully susceptible right now. 1

What to Expect If You Get Infected

• Symptoms begin 12-48 hours after exposure with acute onset of nausea, vomiting, and diarrhea. 2, 3
• Illness typically lasts 12-72 hours in healthy adults and is self-limited. 2, 3
• About 10% of infected people require medical attention for dehydration. 2, 3
• Treatment is supportive with oral rehydration therapy; there are no antivirals available. 2, 3

Bottom line: Get soap immediately, wash your hands properly and frequently, and understand that your previous infection two years ago provides you with essentially zero protection against current norovirus strains. 1, 2