True about Diptheria -

Ans. is 'b' i.e.,Incubation period 2-5 days . Diptheria is caused by Gram positive bacilli, Corynebacterium diphtheriae . Incubation period of most common form of diphtheria ( faucial/ tonsiliopharyngeal diphtheria) is 2-5 days. . For chemoprophylaxis erythromycin or penicillin are used. " Previously immunized asymptomatic household contact should receive booster dose of diphtheria toxoid. Those not fully immunized but asymptomatic contacts should receive immunization for their age".---0.P. Ghai 7th/221 "Lifelong immunity is usually, but not always, acquired after disease or inapparent infection"---health.vic.gov.au> IDAES home > blue book . So, child recovered from illness is already is immune. No active immunization is required.