Which of the following statements is true about the epidemological determinants of measles -

<p> Measles epidemiologic determinants:- AGENT FACTORS:- 1. Agent-RNA paramyxovirus. Only one serotype . The virus cannot survive outside the human body for any length of time. 2. Source-case of measles. 3. Infective material-Secretions of nose,throat and respiratory tract. 4. Communicability- 4 days before the appearance of rash to 4 days after. 5. Secondary attack rate-infection confers life long immunity. HOST FACTORS:- 1. Age- affects viually everyone. More incidence seen in children between 6 months-3years. 2. Sex- equal incidence. 3. Immunity- one attack provides life long immunity. Infants protected upto 6 months of age. 4. Nutrition-severe in malnourished children. Possibly due to poor cell mediated immunity. {Reference: park&;s textbook of preventive and social medicine, 23rd edition, pg no.147}</p>