Is the influenza (flu) vaccine a live vaccine?

Influenza Vaccine Types: Live vs. Inactivated

The influenza (flu) vaccine is available in both inactivated and live attenuated forms, but the standard flu shot most people receive is an inactivated (killed) vaccine, not a live vaccine.

Types of Influenza Vaccines

• There are two main types of influenza vaccines available:

  • Inactivated influenza vaccine (IIV) - administered intramuscularly as an injection 1
  • Live attenuated influenza vaccine (LAIV) - administered intranasally as a spray 1

• The inactivated influenza vaccine contains killed virus particles that cannot cause infection 1

• The live attenuated influenza vaccine contains live but weakened (attenuated) influenza viruses that are:

  • Temperature-sensitive - limited in replication at normal body temperature
  • Cold-adapted - able to replicate efficiently only at lower temperatures
  • Attenuated - producing mild or no symptoms related to influenza infection 1

Key Differences Between Vaccine Types

Inactivated Influenza Vaccine (IIV)

• Administered via intramuscular injection 1
• Contains killed virus particles 1
• Approved for persons aged 6 months and older 1
• Can be given to people with chronic medical conditions 1
• Standard formulation for most people receiving flu vaccination 1

Live Attenuated Influenza Vaccine (LAIV)

• Administered via intranasal spray 1
• Contains live but weakened virus 1
• Approved only for healthy persons aged 2-49 years 1
• Cannot be given to people with certain medical conditions, including asthma, immunocompromised states, and pregnancy 1
• Recipients may shed vaccine virus for up to 2-7 days after vaccination 1

Restrictions on LAIV Use

The live attenuated vaccine should not be given to:

• Persons younger than 2 years or 50 years and older 1
• Persons with asthma, reactive airways disease, or other chronic disorders 1
• Immunocompromised individuals 1
• Pregnant women 1
• Children or adolescents receiving aspirin or salicylates 1
• Healthcare personnel who work with severely immunocompromised patients 1
• Solid organ transplant recipients 1

Efficacy Considerations

• Both vaccines stimulate an immune response, though through somewhat different mechanisms 2, 3
• Efficacy can vary by season, circulating strains, and recipient age 4
• In some studies, inactivated vaccines have shown higher efficacy than live attenuated vaccines in adults 4
• The live attenuated vaccine has shown good efficacy in children in some studies 2

Common Pitfalls and Caveats

• Many people incorrectly assume all flu vaccines are the same type
• The standard flu shot that most people receive is an inactivated vaccine, not a live vaccine 1
• Special consideration must be given when vaccinating immunocompromised patients or their close contacts, as LAIV is contraindicated for immunocompromised individuals 1
• Healthcare workers caring for immunocompromised patients should preferentially receive inactivated vaccine rather than LAIV 1
• If household contacts of immunocompromised individuals receive LAIV, good hand hygiene and minimizing contact with secretions should be emphasized 1