Understanding Norovirus: Staying Safe Amid Winter Surge

Norovirus, more commonly known as the "winter stomach bug," is an invisible yet pervasive threat, particularly during the colder months. As of December 2024, the U.S. has seen a worrying surge in Norovirus outbreaks, with the highest levels reported for this time of year since 2012.¹ In order to understand the burden of Norovirus, and why mRNA technology has the potential to be an important tool for combating it, it’s important to look at how it spreads and evolves.

The Burden of Norovirus

Norovirus is a leading cause of acute gastroenteritis worldwide, resulting in significant morbidity and economic losses.

• Global Impact: Norovirus causes 685 million cases annually, including 200 million in children under five. It accounts for 50,000 child deaths, primarily in low-income countries.²

• U.S. Statistics: Each year, norovirus causes 109,000 hospitalizations, 465,000 ER visits and 900 deaths, predominantly in adults aged 65 and older.³

• Economic Toll: The virus costs $2 billion annually in the U.S. alone due to healthcare expenses and lost productivity, with global costs soaring to $60 billion.⁴

Norovirus doesn't discriminate—it affects people of all ages. However, young children, older adults and immunocompromised individuals face the highest risks of severe outcomes.⁵

Why Norovirus Is So Challenging

The virus is exceptionally contagious and can spread through contaminated food or water, contact with contaminated surfaces or close contact with an infected person.

The existence of diverse norovirus genotypes and apparent lack of lifelong immunity from natural infection means individuals can be infected multiple times throughout their lives.⁶,⁷ Currently, there is no approved vaccine for Norovirus, so there are a few important practices to stay safe.⁸

1. Practice Good Hygiene:

   • Wash your hands thoroughly with soap and water, especially before eating and after using the bathroom.

   • Use hand sanitizers only as a supplement; they are less effective than soap and water against Norovirus.

2. Handle Food Safely:

   • Wash fruits and vegetables thoroughly.

   • Ensure seafood is cooked to the appropriate temperature.

   • Avoid preparing food if you are feeling unwell or recovering from illness.

3. Clean and Disinfect:

   • Clean high-touch surfaces regularly with a bleach-based cleaner.

   • Wash contaminated laundry immediately, using gloves and hot water.

4. Stay Home When Sick:

   • Norovirus can remain contagious for several days after symptoms resolve. Stay home for at least 48 hours post-recovery to prevent spreading the virus.

The Potential of mRNA

mRNA technology has the potential to be a groundbreaking tool for combating Norovirus due to several key advantages. As previously mentioned, Noroviruses have broad variability, and the prevalent circulating genotypes can change from year to year.⁹ Given this, vaccine development has been challenging to date. To provide coverage against >70-80% of prevalent circulating Norovirus genotypes in a given year, a multivalent vaccine design is required. Given its adaptable and scalable nature, mRNA technology could be an important tool for combatting Norovirus.¹⁰

There are currently no licensed vaccines for Norovirus, despite the significant burden it places on public health. At Moderna, we embrace the responsibility to explore mRNA’s full potential in addressing the global burden of Norovirus and are proud to have two vaccine candidates in our enteric vaccines pipeline, one of which is currently in Phase 3.

¹https://www.cdc.gov/norovirus/php/reporting/norostat-data.html

²https://www.cdc.gov/norovirus/data-research/index.html#:~:text=Norovirus%20worldwide&text=Worldwide%2C%20norovirus%20annually%20causes%20on,deaths%2C%20mostly%20in%20developing%20countries

³https://www.cdc.gov/norovirus/data-research/index.html#:~:text=Norovirus%20worldwide&text=Worldwide%2C%20norovirus%20annually%20causes%20on,deaths%2C%20mostly%20in%20developing%20countries

⁴https://pmc.ncbi.nlm.nih.gov/articles/PMC8171800/

⁵https://www.cdc.gov/norovirus/about/index.html#:~:text=Who%20is%20at%20risk,eat%20raw%20or%20undercooked%20shellfish.

⁶Chhabra P, de Graaf M, Parra GI, Chan MC, Green K, Martella V, et al. Updated classification of norovirus genogroups and genotypes. J Gen Virol. 2019; 100(10):1393-406.

⁷Simmons K, Gambhir M, Leon J & Lopman B. Duration of immunity to norovirus gastroenteritis. Emerging Infectious Diseases. 2013; 19(8):1260-7.

⁸https://www.cdc.gov/norovirus/about/index.html#:~:text=You%20can%20get%20norovirus%20illness,exactly%20how%20long%20protection%20lasts.

⁹Carlson KB, Mahood D, Nunna N, Viscidi E, Bollman BA, Arunkumar GA, et al. Global prevalence of norovirus genotypes across two decades of acute gastroenteritis cases. ID Week 2024. Poster number 1827570.

¹⁰NoV, norovirus; VP1, major capsid protein; Cannon et al Emerging Infect. Dis. 2021; Calderwood et al. Clin Infect Dis 2022; Carlson KB et al npj Vaccines 2024