Is the Flu Vaccine Live?
The flu vaccine is available in both inactivated (killed) and live attenuated forms, but the vast majority of flu vaccines administered are inactivated vaccines that contain killed virus and cannot cause infection. 1, 2
Types of Influenza Vaccines
Inactivated Influenza Vaccines (IIV)
- Inactivated vaccines contain killed influenza viruses that have been chemically inactivated and rendered completely noninfectious. 1, 2, 3
- These vaccines are administered via intramuscular injection and are approved for anyone aged ≥6 months, including pregnant women, elderly persons, and those with chronic medical conditions. 1, 3, 4
- The manufacturing process involves growing vaccine viruses in embryonated hens' eggs, then using chemical compounds to kill and inactivate the viruses, creating purified surface antigen preparations. 1, 2
- Because the viruses are killed, inactivated vaccines cannot produce signs or symptoms of influenza virus infection. 1, 3
Live Attenuated Influenza Vaccine (LAIV)
- LAIV contains live but weakened influenza viruses that are temperature-sensitive, cold-adapted, and attenuated. 3, 4
- This vaccine is administered via intranasal spray and is approved only for healthy, non-pregnant persons aged 2-49 years. 1, 3, 4
- LAIV has the potential to produce mild signs or symptoms related to influenza infection because it contains live virus, though the viruses are attenuated and cannot cause typical influenza illness. 1, 3
- Recipients may shed vaccine virus for 2-7 days after vaccination. 3
Key Clinical Distinctions
Who Should NOT Receive LAIV
- LAIV is contraindicated in immunocompromised persons, pregnant women, children <2 years, adults ≥50 years, persons with asthma or chronic medical conditions, and those taking aspirin/salicylates. 1, 3
- Healthcare workers caring for severely immunocompromised patients should preferentially receive inactivated vaccine rather than LAIV. 3
- Solid organ transplant recipients should never receive LAIV. 3
Who Should Receive Inactivated Vaccine
- Inactivated vaccines are appropriate for all persons aged ≥6 months, including high-risk groups such as pregnant women, elderly persons, immunocompromised individuals, and those with chronic medical conditions. 1, 3, 4
Common Pitfall to Avoid
The most important clinical distinction is that inactivated flu vaccines contain killed virus and cannot cause influenza infection, while LAIV contains live attenuated virus with specific contraindications. 1, 3 When patients ask "is the flu vaccine live," they are typically receiving an inactivated vaccine administered by injection, which contains only killed virus particles. 2, 3