The answer to the question above is 2. The girl should receive 2 doses of influenza vaccine this flu season. Basically, influenza is contagious. This virus can spread from person-to-person. Children at this age is highly susceptible to this kind of serious illness because their immune system is not fully competent enough compared to adults. Even adults can acquire this illness if they are immunocompromised. This is the reason why children need 2 doses.