Norovirus outbreaks and the necessity of a future NoV vaccine

Dear Editor,

Norovirus (NoV) is a viral illness considered the leading cause of acute gastroenteritis (AGE) for all ages globally. An estimated 685 million cases of norovirus are reported annually, including 200 million cases among children under 5. The burden of NoV is significant, causing an estimated 200,000 deaths yearly, including 50,000 child deaths, primarily impacting low-income countries. It has been estimated to cost $60 billion globally due to healthcare costs and economic losses. ¹ Just recently, NoV, also known as “stomach flu” or “vomiting bug,” has been spiking across the United States. From August 1, 2024, to December 11, 2024, 495 NoV outbreaks were reported by the 14 states participating in the U.S. Centers for Disease Control and Prevention’s (CDC) noroSTAT surveillance program. This is an increase from the 363 outbreaks from the same states during the previous year, 2023.

Last year, 2024, a NoV outbreak hospitalized more than 300 in a village on the shore of Lake Garda in Italy. At the Athletic World Championships 2017 in London, at least 30 athletes and team members at the world athletics championships were infected in a suspected Nov outbreak. In 2012, there was a case in Germany where a medium-sized cruise ship had to be put under quarantine in Wiesbaden after 67 tourists fell ill because of the virus. ² In Baguio City, Philippines, another outbreak was declared last January 2024, with 3087 self-reported NoV-related cases. The majority of those who fell ill are female, aged 21–30, presenting symptoms like diarrhea, abdominal cramps, and vomiting. ³ One of the most number of outbreak cases was recorded in China, with a total of 419 outbreaks, which were reported in the 394 articles being evaluated in a study from 2000 to 2018. ⁴ Currently, the steep surge of NoV cases, especially in the United States, is due to the new strain called GII.17[P17]. The new strain has been active around the country, including in many cruise ship outbreaks where there is a lower population immunity. More than 7 in 10 outbreaks have been linked to this new strain this season. ⁵

It is important to reiterate that no currently available and licensed NoV vaccines exist. The primary barrier to developing an effective human norovirus (HuNoV) is the lack of a robust and reproducible in vitro cultivation system. However, NoV vaccine development is advancing. HuNoV immunogens alone or combined with other viral immunogens have been designed to assess whether they can induce protective immune responses against different viruses simultaneously. In addition, monovalent and multivalent vaccines from different HuNoV genotypes, including GI and GII HuNoV virus-like particles, have been assessed to induce broad protection. ⁶

Despite the positive and promising development of NoV vaccines, one barrier that can hinder a successful vaccination program in the future is still vaccine hesitancy. It is necessary to address this barrier to increase the uptake of vaccines for future licensed vaccines. One critical intervention is a massive and comprehensive information campaign regarding the benefits and efficacy of vaccines. All forms of media, especially the various popular social media platforms, such as Facebook, YouTube, TikTok, Instagram, etc., must be fully utilized by the government through its healthcare department. The battle against health misinformation or “fake news” regarding the vaccine must also be included in the campaign, and with this, enhancing the public’s health and media literacy is vital. This is where regular educational and health programs are needed to battle unreliable sources of information. Another intervention is the incentive or reward system for those willing to get vaccinated. This program became popular during the COVID-19 pandemic when massive food was scarce in the Philippines. Incentives such as cash, groceries, and rice are distributed to convince more people to vaccinate. Mobile vaccination is another strategy. Since some people have difficulty going to vaccination sites due to transportation expenses or busy schedules, mobile vans/clinics will go to public places to serve as vaccination sites. Lastly, the use of “vaccine champions” who will serve as role models can make a significant impact in addressing vaccine hesitancy. These people are government officials, healthcare providers, and community and religious group leaders, who will get the vaccine first and show the public that everything is beneficial for everyone’s protection.

As everyone awaits a licensed and effective NoV vaccine, it is necessary to follow the minimum health protocols to prevent the spread of the virus. Practicing personal hygiene always contributes to cleanliness and the prevention of any disease. The barrier of vaccine hesitancy must be addressed because it deprives everyone of living in a safe and healthy environment. With the help and collaboration from the different sectors of society and the public’s full cooperation, there will surely be a robust fight against NoV-caused illnesses and, thus, a healthier society.