Children younger than 3 years old receive roughly the same amount of protection from the flu vaccine regardless of which method (injection, nasal spray, or one of each) is used to give the two recommended doses to them, according to a new federal study. 
The US National Institute of Allergy and Infectious Diseases (NIAID) found that “children younger than three years old receive roughly the same amount of protection from the flu vaccine regardless of which method (injection, nasal spray, or one of each),” although children who receive one or more doses of the nasal vaccine showed the broadest immune response.
Researchers concluded that the “best regimen for children younger than 24 months might be one injected dose followed by one live, attenuated dose of the seasonal flu vaccine.”
Both work well, but nasal spray produces broadest immune response in youngsters, research shows.