Current research suggests that some people are more susceptible to viral gastroenteritis than others. In a study where volunteers were infected with Norowalk virus, (anyone want to volunteer for that?) 82% became infected and 18% did not (lucky ducks). Of the 82% that became infected about 1/3 were asymptomatic and did not get sick (more lucky ducks)1. However, these asymptomatic people were carrying and transmitting the virus without knowing it.
A person’s blood type has also been shown to affect their susceptibility2. For the Norwalk virus strain, it has been determined that people with type B blood are less susceptible and people with type O blood get the sickest3. However, for another strain of norovirus, people with type O blood were less affected4. Here is a research paper that indicated that people with type A blood are less susceptible to norovirus.6 So, different strains of the virus affect people differently and scientists are still trying to figure it out.
There is something else that is important in determining norovirus susceptibility. The GII norviruses, including GII.4 Sydney, rarely infect people who are "non-secretors". People who are non-secretors have mutations in the genes called FUT2. Because of these mutations, these people do not express their ABO blood group antigens in their saliva or gastrointestinal tract5. It is thought that Norovirus needs to bind to these ABO antigens in order to infect a person. Since these people don't have the antigens in their intestinal tract, they usually don't get sick from norovirus! The company 23 and Me USED to do this genetic test, but they are not allowed to do it anymore. I had my DNA evaluated by 23 and Me. As I expected, I am NOT resistant to norovirus.
--Annie Pryor, Ph.D.
I have never had the stomach flu and I've never caught it from my kids. I have blood type B+.