The Caliciviruses, Reoviruses and Astroviruses

Cement foundations and a few scattered pillars are all that now remains of the Bronson Norwalk Elementary School in Ohio in the United States. While the school was demolished more than 40 years ago, for the virus that made its first sickening appearance there, the past four decades have been ones of prolific growth and spread.  

The first outbreak of Norwalk Virus—now known as Norovirus—produced “a lot of puking kids”, according to doctors dealing with it at the time. But that was just the start.  Since Norovirus sparked this first known outbreak in Ohio in 1968, it has grown to become a world leader as a cause of vomiting and diarrhoea, with almost 700 million people being struck down by it each year.  

In 2012, scientists in Britain eager to investigate how Norovirus manages to be so prolific and resilient even created a "humanoid simulated vomiting system".  

“Vomiting Larry”—as the system was nicknamed—showed that Norovirus particles can travel an astonishing three metres (almost 10 feet) in an episode of projectile sickness. And since it takes fewer than 20 virus particles to infect someone, each droplet of vomit or gram of faeces from an infected person can contain enough virus to infect more than 100,000 people.

The illness that Norovirus causes, also known more generally as gastroenteritis, can also be caused by a range of other viral disease threats. These include the relatively well-known Rotavirus, which is the leading cause of fatal diarrhoea around the world and causes more than 250 million infections globally each year, and the less well known Human Astrovirus.  

All three use a similar mode of attack: entering the human body via what is known as the faecal-oral route. This means they get in when people fail to wash their hands after going to the toilet and then put their fingers in their mouth, or when splashes of vomit from an infected person find their way via contaminated surfaces and unwashed hands into a new victim’s digestive system.  

While they share many rather gross common traits, these persistent viruses come from three different families of pathogens—the Calciviruses, the Reoviruses and the Astroviruses. All three are among The Viral Most Wanted

Scientists relentlessly pursued a number of lines of enquiry on the main culprit in the Reovirus family, with their work bearing fruit first in 1998 and again in 2006 with the development of vaccines against Rotavirus.  Now, the discovery of Rotavirus as a major cause of deadly diarrhoea and the subsequent development and widespread use of multiple safe and effectives vaccines to prevent it are described by global health experts as among the most important contributions of medical research to global human health.

The World Health Organization first recommended including the Rotavirus vaccine in national immunisation programmes in the Americas and the European region and in 2005. Four years later, this advice was extended to all regions of the world. Today, these vaccines are used in more than 100 countries and have contributed to dramatic declines in hospitalisations and deaths from diarrhoea.

For Caliciviruses, researchers are also following multiple lines of enquiry in the pursuit of safe and effective vaccines to prevent infection. For Norovirus, the U.S. biotech company Moderna is developing a vaccine called mRNA-1403 that uses messenger RNA technology and is designed to target multiple strains of the virus. A large global late-stage clinical trial of this Moderna vaccine started in the summer of 2024.

A separate group of U.S. researchers at the Washington University School of Medicine  is also working on an experimental vaccine against both Rotavirus and Norovirus. The potential dual vaccine, which has yet to be tested in large-scale trials, was designed by incorporating a protein gene from the outer surface of human Norovirus into the genome of a laboratory Rotavirus strain.

For Astroviruses, there are currently no vaccines approved, and disease detectives’ efforts in this field are at relatively early stages—in part due to the comparatively lower threat posed by this viral family as compared to Caliciviruses and Reoviruses.