In this volunteer infection study, volunteers were exposed to varying concentrations of norovirus. In addition, secretor vs. non-secretor status was tested via functional and genetic tests. Among the secretors, combining all different doses, 34 out of 55 became infected after exposure. Of the non-secretors, none were infected, regardless of dose (0 out of 22), a p-value of 0.00016 using a two-tailed Fisher’s Exact test.
Norwalk virus-like particles were found to bind only saliva from secretor (Se+) volunteers.
The paper also describes the impact of Norovirus in the US as “an estimated 23,000,000 infections, 50,000 hospitalizations and 300 deaths per year”.
A recent review paper compiling various studies regarding norovirus susceptibility and genotypes (secretor status and ABO blood types). These studies are both voluntary infection studies, and cases of natural infections. FUT2, along with FUT1, is responsible for expression of the H antigens — these are what become modified to become A, B, and O types. FUT1 is responsible for expression in red blood cells, while FUT2 is responsible for secretion in mucosal tissues & saliva. This variant (FUT2-W154X) results in “non-secretor” status: individuals homozygous for this do not express the ABO antigens on their mucosal tissues / saliva (but still do on their red blood cells).
In general non-secretors are found to be almost completely resistant to norovirus. Notably, there are reports of some strains where non-secretors are susceptible. Consistent with this, binding studies using virus-like particles find a secretor-dependent binding pattern. These seem to be an exception among norovirus strains, however.
Groups have also reported variable binding to the different ABO in some strains (while other strains do not have such a bias) — for example, blood type B doesn’t seem to be bound by the GI.1 strain (while O, A, and AB are). This may explain why there are some reports of variability in norovirus susceptibility base on ABO type (with O generally more sensitive).