<prompt> True about influenza ?Incubation period 2-3 weeksMost infections are subclinicalType-A virus causes Reyes syndromePandemic is caused by Type-B virus  <response>: Ans. is b i.e., Most infections are subclinical Influenza Influenza virus a RNA virus, belongs to ohomyxovirus. There are three viral subtypes : i Type A causes all pandemics and most epidemics; type B; and type C not circulating currently. Currently the influenza viruses circulating in the world are : 111 N, of type A causes swine flu; H2 N2 of type A; H3 N2 of type A ; H5 NI of type A causes birdflu or an influenza; H7 N9 of type A caused epidemic of an influenza in China in 2013; and type B. Influenza shows cyclic trend with epidemic occuring every 2-3 years in case of influenza - A and every 4-7 years in case of influenza-B. Pandemics are caused by only influenza - A every 10-15 years. Influenza affects all ages and both sexes. Source of infection of influenza is a clinical case or subclinical case. Major reservoir of influenza virus exists in animal and birds. Incubation period is 18-72 hours. Most of the infections are subclinical. Clinical cases present with cough, fever, myalgia and headache. 