Experimental design and virus shedding of AERO, intranasal and contact challenge. A Pigs were challenged with 1 × 104 EID50 (low) or 1 × 107 EID50 (high) of A/Sw/Eng/1353/09 virus by aerosol (AERO) or intra-nasally (IN). After 2 days three naïve pigs were co housed with each of the AERO high or IN high animals and after further 2 days moved to separate rooms. Horizontal lines indicate the time scale of the experiment and the vertical bars show challenge, time of contact and sacrifice. B Viral titers in nasal swab suspensions for indicated groups. The viral titres are represented by markers. Each line represents an individual within the indicated group.