In contrast to SARS, which is contagious only once fever breaks out, novel H1N1 is contagious from the day before symptoms strike until around seven days after. Indeed some 30 % of those who contract the illness experience no fever at all. Thus screening cannot be achieved just by use of ultraviolet sensors, and H1N1 prevention efforts have quickly moved from airports and borders into communities.
不同於 SARS 在發燒時才具有傳染性，新流感的感染性更強，在發病前一天、後 7 天都具有感染力，有 3 成患者甚至不發燒，無法以紅外線感測異狀，因此新流感的防治很快就從機場及海關棄守，轉而投入社區防治。