Norovirus Vaccine - A Step Closer to Safety

Introduction:

Noroviruses cause acute gastroenteritis in the United States and worldwide. These infections are more common in the fall and winter months. There are no licensed vaccines available for noroviruses in the world. Vaccinations are yet to be finalized as they are under trails yet. Widespread vaccination can minimize the norovirus burden and can benefit the entire population. Many additional norovirus platforms are under development which may help improve the norovirus vaccine in the future.

Is There a Vaccine for Norovirus?

No, There has been never a vaccine licensed for norovirus in the world. Though many candidates are under development, projections state that the effective vaccine could have both economic and clinical benefits.

What Is the Effectiveness of Norovirus Vaccines?

It was noted that by the age of five years, almost all children would have been affected by at least one norovirus infection, and many would have many infections and disease episodes. Hence, almost all older children have pre-existing antibodies from natural infection.

Immunizing these age groups involves only boosting pre-existing immunity. Therefore, only a single dose or a limited number of doses may be needed for a protective immune response.

Infants and young children will not have antibodies from previous infections. Hence they may need multiple doses of vaccines.

The predictions suggest that a norovirus vaccine with a 50 percent efficacy rate may be protective for 12 months. This could prevent around 1 million to 2.2 million norovirus cases per year in the United States.

What Are Norovirus Vaccine Safety and Potential Side Effects?

The norovirus vaccine was found to be well tolerated. It did not show any dose-limiting toxicities. The adverse effects were found to be mild to moderate. The side effects include sudden nausea, vomiting, diarrhea, stomach pain, tiredness, weakness, muscle pains, and fever.

What Are the Types of Norovirus Vaccines?

Norovirus vaccines are of three types. These include:

1. Non-replicating virus-like particles (VLPs).

2. P particles.

3. Recombinant adenoviruses.

All these vaccine developmental platforms have challenges and limitations.

VLPs are protein structures that are similar to the organization and conformation of wild-type viruses. P particles are nanoparticles from the norovirus’s capsid domain. Adenoviruses are vector-based systems that express capsid proteins that induce cellular, humoral, and mucosal immune responses. It was noted that many vaccine candidates have reached different phases of clinical trials.

What Is the Importance of Norovirus Vaccination?

The noroviruses can cause epidemic gastroenteritis in all age groups. These are linked with high-profile outbreaks in hospitals, nursing homes, cruise ships, and the military. The norovirus vaccination can help decrease the burden of norovirus disease. This can benefit the entire population.

Targeted vaccination of particular groups of the population like healthcare workers, may further help decrease the disease burden and deaths in vulnerable populations.

What Is the Commotion About the Norovirus Vaccine?

It can be disheartening to know that for several years, there was no vaccine to prevent the incidence of Norovirus disease. However, it is vital to understand that not everyone is susceptible to any one strain of Norovirus. A subset of the world's population has a genetic makeup that prevents particular viral strains from infecting. Therefore, it is suspected that not everyone infected with the virus shows symptoms. This further complicates the efforts required to prevent and control the spread of the virus. Additionally, because the virus is shed in large amounts in vomit and feces and is persistent and resistant, it is clear that a Norovirus outbreak can result from one ill individual or contamination event, thereby necessitating the need for a vaccine to minimize casualties and maximize prevention.

Owing to advancements in medicine and research today, several studies have been undertaken to create a novel vaccine that can help contain Norovirus disease. The studies, however, have been done on virus-like particles that mimic the Norovirus and on animals such as mice. A few of the vaccines under trial are as follows -

• The Takeda Norovirus vaccine.

• The Vaxart Norovirus vaccine.

• The NVSI Norovirus vaccine.

• The Longkoma Norovirus vaccine.

The studies have concluded that the vaccines can help reduce the symptoms, such as vomiting and diarrhea, by a significant proportion, if not eliminate the disease. A substantial reduction in such symptoms can help in faster recovery in a large part of the population, and prevent further casualties, especially in individuals with other debilitating conditions, which, combined with the Norovirus disease, can prove fatal.

What Are the Challenges in the Development of a Vaccine Against Norovirus Disease?

Several factors challenge scientists when creating a novel vaccine. The obstacles include the following factors -

• The Norovirus has a broad spectrum of antigenic and genetic diversity; an infection by a single strain does not confer long-term immunity.

• Infections with Noroviruses trigger cellular and humoral immunological reactions. Although antibody-mediated immunity is generally well understood, little is known about the cellular immune response to Norovirus infection, further complicating the process.

• The human Norovirus cannot be grown under artificial conditions, such as in cell cultures.

Conclusion

Although it may seem like food poisoning, the Norovirus disease differs from food poisoning and can be highly debilitating for the affected. It can result in many symptoms, rendering an individual weak and dehydrated. Such individuals experience bouts of vomiting and diarrhea and should be monitored closely, ensuring proper fluid intake to prevent dehydration and its unkind consequences. Like any viral disease, it runs its due course and takes time to be flushed out from the system. Considering its high rate of infectivity, The World Health Organization has prioritized creating a vaccine that can help prevent and contain this disease. Until then, palliative care and isolation of the affected individuals remain the only methods to combat this disease.