H1n1 flu symptoms: - acute respiratory illness - fever - cough - sore throat - body aches - headaches - chills and fatigue - diarrhea and vomiting h1n1 flu is a highly contagious viral infection caused by the influenza a (h1n1) virus. the symptoms of h1n1 flu are listed in the box below. an antiviral agent administered within 48 hours of the appearance of symptoms can reduce the severity of the illness. why is it important to administer an antiviral agent to an infected person within 48 hours of the appearance of symptoms? a. the h1n1 virus is dormant in cells. b. the h1n1 virus replicates quickly. c. the h1n1 virus does not mutate. d. the h1n1 virus is transmitted through a vector host, such as a mosquito.