Delivery

• The flu shot is given in a single arm injection for adults and a second injection a month later for children younger than 9, according to the Centers for Disease Control and Prevention.
  
  The flu spray, which is also known as live attenuated influenza vaccine or LAIV, is delivered in a spray to each nostril. The spray is administered twice to increase to ensure effectiveness.
  
  

Difference in Makeup

• The flu vaccine contains inactivated viruses, meaning the viruses have been killed. The presence of these viruses--even though they are not living--helps the body to build immunity against the flu.
  
  The nasal spray contains live--but very weak--viruses. The spray vaccine also helps the body to build up immunity to the flu virus. In very rare instances, the vaccine can be transmitted to others because the spray is placed in the nasal passages, and a person can pass the viruses on by sneezing or breathing.
  
  

Qualifications

• The nasal spray is not recommended for all ages and demographics because the spray contains live viruses. The Centers for Disease Control and Prevention says the following groups should not receive the spray: children younger than age 2; children with asthma; adults older than 50; pregnant women; those with chronic medical conditions or those who are ill and having difficulty breathing.
  
  The shot is recommended for almost all ages, excepting those younger than 6 months and those who are allergic to eggs, which is what the virus is grown and harvested in.
  
  

Side Effects

• Neither vaccine delivery method causes the flu, however both may cause some side effects. The spray causes side effects such as a runny nose, headache, sore throat or cough in adults and muscle aches, nausea, fever and respiratory problems, such as coughing or wheezing, in children.
  
  Side effects of the shot include soreness or swelling where the injection was given as well as muscle aches and a low-grade fever.
  
  

Effectiveness

• The effectiveness rate of each administration method most often depends upon the person's age: the shot is more effective in children and is helpful in reducing the overall spread of flu in the community where the flu spray was given, according to everydayhealth.com.
  
  However, in adults the flu shot is significantly more effective than the spray: according to the Mayo Clinic, the spray was between 30 and 57 percent effective in adults compared to the 70 to 90 percent effectiveness of the shot in adults younger than 65.