Third batch of Twelve Days of Norovirus answers – NoroCORE Food Virology

Third batch of Twelve Days of Norovirus answers

A large cluster of norovirus plushiesWe here at NoroCORE headquarters continue to be impressed by the great answers we have been receiving to our Twelve Days of Norovirus contest. Here is the third batch of question answers!


Question 7: There seems to be a lot of norovirus going around and Granny Grace is worried about catching it. Explain to Granny Grace the main ways people can catch norovirus.


Everyone gave thorough answers for this one, and you were spot on! As a fecal-oral (and vomit-oral) virus, you get norovirus by coming into contact with the stool and vomit of someone who is already infected with the virus, and letting those viruses enter through the mouth. This includes touching a surface that is contaminated with the virus, having close person-to-person contact with someone who is infected (such as sharing eating utensils), or consuming food or water that is contaminated with the virus.


Question 8: Neighbor Matt said some of his family, including Granny Grace, are now sick with norovirus but he feels fine. You invite him to Christmas dinner; do you think it’s possible for him to transmit norovirus even though he’s not showing symptoms?


It’s true, people can be asymptomatic (not showing norovirus symptoms) but still be shedding the virus. As many as 30% of norovirus infections are thought to be asymptomatic.

There have actually been a couple of outbreaks tied to people who were never sick but tested positive for the virus. Earlier this year, thirteen schools in Japan experienced norovirus outbreaks at the same time and had to temporarily close. It was quickly realized that the school cafeterias had all received bread from the same company, and testing of the bakery facility’s workers identified three people who had the virus. These three workers had been in direct contact with the bread that went to the schools, but none of them had ever had norovirus symptoms. It was a really interesting story, and you can read more about it here on our blog. Understandably, having asymptomatic people who still shed the virus complicates prevention and control measures.


Question 9: Neighbor Matt is worried that Granny Grace is going to catch norovirus again. How long do you think Granny Grace is immune to norovirus now that she’s had it?


We had some very detailed and astute answers on this one, and everyone got the take home message that it varies from person to person and from strain to strain. Researchers are still trying to understand how immunity to norovirus works, because it is so variable and because our antibodies to the virus do not always seem to be protective, or may only be protective for a short period of time.

We have a few human challenge studies to draw upon, which the CDC does a nice job of summarizing. In these studies, volunteers are given the virus and monitored in a clinical setting. Based on these studies, immunity to a specific strain of the norovirus is thought to be somewhere between six months and two years, but it could also be more like 8 weeks, and then there are people who may be immune for longer. It is also important to remember that there are many types of norovirus, and immunity to one strain may not mean you won’t get infected with a different strain down the road.

One caveat is that these human challenge studies give people higher doses of the virus than they would probably come into contact with naturally, so it may be that the immune system is doing a better job than we give it credit for.


Just three more questions to go before we announce our contest winner! Remember, each answered question is an entry into the drawing!


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