What is the difference between the flu vaccine shot and the nasal spray (Intranasal influenza vaccine)?

Flu Vaccine: Shot vs Nasal Spray

For most patients, the intramuscular flu shot (inactivated influenza vaccine) is the preferred option because it can be given to anyone 6 months and older, including those with chronic medical conditions, while the nasal spray (live attenuated influenza vaccine) is restricted to healthy, non-pregnant individuals aged 2-49 years only. 1, 2

Key Differences Between the Two Vaccines

Vaccine Composition and Administration

• The flu shot contains killed (inactivated) virus particles that cannot cause infection, administered via intramuscular injection into the deltoid muscle (adults/older children) or anterolateral thigh (infants/young children) 1, 2
• The nasal spray contains live but weakened (attenuated) viruses that are cold-adapted and temperature-sensitive, administered as 0.1 mL spray into each nostril 1, 2
• Both vaccines contain the same three influenza strains (two influenza A and one influenza B), are grown in eggs, and must be given annually 1

Age and Population Restrictions

Inactivated Vaccine (Shot):

• Approved for anyone ≥6 months of age, including those with chronic medical conditions 1, 2
• Can be given to pregnant women, immunocompromised patients, and those with asthma or other chronic diseases 1
• The only option for infants 6-23 months, adults ≥50 years, and anyone with underlying health conditions 1, 2

Live Attenuated Vaccine (Nasal Spray):

• Approved ONLY for healthy, non-pregnant persons aged 2-49 years 1, 2
• Absolutely contraindicated in multiple populations 1, 2:
  • Children <2 years or adults ≥50 years
  • Anyone with asthma, reactive airways disease, or chronic pulmonary/cardiovascular conditions
  • Immunocompromised individuals or those on immunosuppressive therapy
  • Pregnant women
  • Children/adolescents on aspirin or salicylate therapy
  • Anyone with diabetes, renal dysfunction, or hemoglobinopathies
  • Solid organ transplant recipients 1

Special Considerations for Healthcare Settings

• Healthcare workers caring for severely immunocompromised patients should preferentially receive the inactivated vaccine rather than nasal spray due to theoretical risk of viral transmission 1, 2
• If household contacts of immunocompromised individuals receive nasal spray, they should minimize contact with the immunocompromised person for 7 days post-vaccination, as vaccine virus can be shed for 2-7 days 1, 2
• The inactivated vaccine is preferred for close contacts of transplant recipients 1

Efficacy Considerations

• In young children (6 months to 7 years), the nasal spray has shown superior efficacy with pooled efficacy of 83% compared to 59% for the shot in adults 3
• For adults aged 18-65 years, the inactivated vaccine demonstrates 59% efficacy against virologically confirmed influenza 3
• Recent data from 2023-24 season shows vaccine effectiveness of 59-67% in children and 33-49% in adults for preventing outpatient influenza visits 4

Dosing Differences

Inactivated Vaccine:

• 0.25 mL for children 6-35 months; 0.5 mL for ≥36 months and adults 1, 5
• Children <9 years receiving vaccine for first time need 2 doses ≥4 weeks apart 1, 5

Nasal Spray:

• Single 0.2 mL dose (0.1 mL per nostril) 1
• Children <9 years receiving vaccine for first time need 2 doses ≥6 weeks apart 1

Common Pitfalls to Avoid

• Do not give nasal spray to anyone with nasal congestion, as it will impede delivery to nasopharyngeal mucosa 1
• Never assume a "healthy" child qualifies for nasal spray without screening for asthma/reactive airways disease, particularly in children aged 2-4 years with history of wheezing 1, 6
• Do not give nasal spray to children on aspirin therapy (e.g., juvenile idiopathic arthritis, Kawasaki disease) due to risk of Reye syndrome 1

Cost and Practical Considerations

• The nasal spray is more expensive than the intramuscular vaccine 1
• The shot requires needle injection, which some patients prefer to avoid, but this must be weighed against the extensive contraindications of the nasal spray 1

Bottom line: Unless the patient is a healthy, non-pregnant individual aged 2-49 years without asthma, chronic disease, immunosuppression, or aspirin therapy, the intramuscular flu shot is the appropriate choice. 1, 2