Baseline characteristics of index patients and household contacts.

*Vaccination defined as vaccination against pandemic influenza in season 2009/10 and trivalent seasonal vaccine in 2007/08, 2008/09 & 2010/11, at least 14 days before symptom onset in index patient or secondary household case. ** Antiviral therapy defined as treatment with oseltamivir or zanamivir within 2 days of symptom onset. *** ILI = Influenza-like-illness.#Asymptomatic = no fever, no cough, no sore throat.##Includes participants from all three intervention groups in seasons 3 and 4.