Table 1 Intake questions asked of participants in GIS

-Age/Male/Female

-Daily occupation? (School/work/home/other)

-Means of transportation? (Car/bike/public)

-How many times per year suffering from cold/ILI? (<2/2–5/>5)

-Recently vaccinated against flu? (Yes/no)

-Do you have asthma or diabetes? (No/asthma/diabetes)

-Do you smoke? (Yes/no)

-Do you follow the recommendations of the Dutch Food and Nutrition Centre? (No/occasionally/daily)

-Do you use vitamins? (No/occasionally/every day)

-Do you follow a diet? (No/vegetarian/veganistic/low-calorie)

-Do you exercise? (<1 hour/week; 1–4 hours; >4 hours per week)

-How many people at home? (Alone/with adults/with adults and children)

-Do the children attend school or nursery? (No/nursery/school)

-Do you have pets? (No/cat(s)/dog(s)/bird(s)/other)