STATISTICAL ANALYSIS
The databases from the two SMV human challenge studies were merged into a single database for analyses. Data were analyzed using SAS 9.4 (SAS, Cary, NC) for Windows. Categorical data were analyzed using a chi-square test or Fisher’s exact test. Continuous variables were analyzed using the t test or Mann-Whitney U test. A P-value of <0.05 was considered significant. Severity scores of illness were calculated using an 18-point numerical scoring system, which was modified from Ruuska and Vesikari’s score system [14]. The scoring system used information on the duration of diarrhea and vomiting, the maximum number of episodes of diarrhea and vomiting within a 24- hour period, and whether the subject experienced certain clinical signs or symptoms, including headache, fever, chill, fatigue, nausea, abdominal cramp, and myalgia (“yes”, “more than one” or “no”). Fever was further graded at four levels (≤37.0°C, 37.1°C-38.4°C, 38.5°C-38.9°C, ≥39°C) by the clinical staff. Table 1 shows the severity score criteria of the modified Vesikari score system [14].