C  

Reasoning:  
• Children under 5 years (including those aged 1–5 years) are recognized high-risk groups for severe influenza complications; stating they are not high-risk is therefore false [Gill, 2015, 25481379].  
• Household secondary attack rates for influenza are commonly around 10–15 %, consistent with option A [Carcione, 2011, 21262182].  
• Detectable viral shedding can begin up to 1–2 days before symptom onset, supporting option B [Ip, 2016, 26518469].  
• Wild aquatic birds constitute the natural reservoir for influenza A viruses, validating option D [Griot, 2007, 18581906].