Norovirus is a highly contagious virus, the primary cause of acute gastroenteritis. This widespread pathogen leads to sudden onset of vomiting, diarrhea, and stomach pain, impacting individuals across all age groups globally. While symptoms typically resolve within one to three days, the virus’s high contagiousness and rapid spread, often through contaminated food, water, or surfaces, contribute to millions of illnesses each year.
Current Status of Norovirus Vaccines
Despite the significant global health and economic burden caused by norovirus, there is currently no licensed vaccine widely available to the general public. Research and development efforts are ongoing, with several vaccine candidates progressing through various stages of clinical trials. The World Health Organization (WHO) has recognized the development of a norovirus vaccine as a high priority since 2016.
Companies like Takeda Pharmaceutical Company, Moderna, and Vaxart are among those actively developing vaccine candidates. These investigational vaccines are in various clinical trial phases, but none have yet received approval. The absence of an approved vaccine highlights the complexities involved in creating effective protection against this resilient virus.
Challenges in Norovirus Vaccine Development
Developing a norovirus vaccine presents several scientific complexities. One significant hurdle is the extensive genetic diversity of noroviruses, which comprise numerous genotypes and genogroups that constantly evolve. This rapid evolution makes it challenging to design a single vaccine that can protect against all or most circulating strains.
Another difficulty stems from the nature of immunity after natural infection, which often does not provide long-lasting protection. This short-lived immunity complicates vaccine design, as a vaccine aims to induce more robust and durable protection than natural exposure.
Additionally, noroviruses have been notoriously difficult to grow in traditional laboratory cell cultures, which has historically hindered research and vaccine production efforts. While recent breakthroughs are improving culturing capabilities, the lack of robust animal models has also posed challenges for testing vaccine efficacy.
Promising Vaccine Candidates
Despite the challenges, research continues to explore different approaches for a norovirus vaccine. A common strategy involves using virus-like particles (VLPs), which are non-infectious shells that mimic the outer structure of the virus. These VLPs can trigger an immune response without causing illness because they do not contain the virus’s genetic material.
Other promising candidates include P-particle and adenovirus-vectored vaccines. Adenovirus-vectored vaccines use a modified adenovirus to deliver norovirus genetic material, prompting an immune response.
Takeda’s bivalent VLP vaccine candidate is one example. Moderna is also developing an mRNA-based vaccine, with a Phase 3 clinical trial underway. Vaxart is developing an oral tablet vaccine.
Preventing Norovirus
Given the current absence of a widely available norovirus vaccine, preventive measures are crucial for limiting its spread. Thorough and frequent handwashing with soap and water is a primary defense, especially after using the bathroom, changing diapers, and before eating or preparing food. It is important to note that alcohol-based hand sanitizers are less effective against norovirus compared to washing hands with soap and water.
Food safety practices are also essential. This includes carefully washing fruits and vegetables, and thoroughly cooking shellfish. Avoiding consumption of potentially contaminated food or water is also advised.
Cleaning and disinfecting contaminated surfaces with bleach-based cleaners is another key preventive action. Finally, individuals experiencing symptoms should stay home to prevent further transmission, particularly avoiding preparing food for others, and should maintain isolation for at least 48 hours after symptoms cease.