Influenza (Flu) Vaccine
Content reviewed against published CDC, AAP, WHO guidelines
Last reviewed:
Key takeaways
- Prevents: Seasonal influenza (flu), Influenza-related pneumonia
- Schedule: 2 doses starting at 6 months (annually, every flu season)
- Effectiveness: Flu vaccine effectiveness varies by season depending on how well the vaccine matches circulating strains.
- Most common side effect: Soreness, redness, or swelling at injection site
How it works
The inactivated influenza vaccine (IIV) contains killed influenza viruses or pieces of the virus (surface proteins hemagglutinin and neuraminidase). These cannot cause flu but stimulate the immune system to produce antibodies. The vaccine is reformulated each year to match the circulating strains predicted by global surveillance. For children 2 and older, a live attenuated intranasal spray (LAIV) may also be used, which contains weakened cold-adapted viruses that replicate only in the cooler temperatures of the nasal passages.
Recommended schedule
| Dose | Age |
|---|---|
| Dose 1 | 6 months (annually, every flu season) |
| Dose 2 | 4 weeks after first dose (first year only, if under 9 years and receiving flu vaccine for the first time) |
Side effects
Common (mild, resolve in 1-2 days)
- Soreness, redness, or swelling at injection site (most common)
- Low-grade fever (10-35% of young children)
- Fussiness or irritability in infants
- Muscle aches
- Fatigue or malaise
- Runny nose or nasal congestion (LAIV nasal spray)
Serious (very rare)
- Severe allergic reaction (anaphylaxis) — approximately 1.3 per million doses
- Guillain-Barre syndrome (GBS) — if there is an increased risk, it is very small, estimated at 1-2 additional cases per million doses
- Febrile seizure — rare, slightly increased when given simultaneously with PCV13 and DTaP
Who should NOT get this vaccine
- Severe allergic reaction (anaphylaxis) to a previous dose of influenza vaccine
- Severe egg allergy with anaphylaxis (precaution; can still receive vaccine under medical supervision or use egg-free formulation)
- Children under 6 months of age (too young)
- LAIV (nasal spray) contraindications: children under 2, immunocompromised, aspirin/salicylate therapy, pregnancy
Effectiveness
Flu vaccine effectiveness varies by season depending on how well the vaccine matches circulating strains. In seasons with good match, the vaccine reduces the risk of flu illness by 40-60% overall. In children, it is approximately 50-80% effective at preventing confirmed influenza and significantly reduces the risk of severe outcomes including hospitalization and death.
Available brands
Fluzone Quadrivalent
Sanofi Pasteur
Fluarix Quadrivalent
GlaxoSmithKline
FluLaval Quadrivalent
GlaxoSmithKline
Flucelvax Quadrivalent
CSL Seqirus (cell-based, egg-free)
Myths vs. facts
Myth: “The flu shot can give you the flu”
Fact: The injectable flu vaccine contains only killed virus or virus fragments — it is physically impossible for it to cause influenza infection. Some people experience mild immune response symptoms (low fever, fatigue) for 1-2 days, which is the immune system responding to the vaccine, not the flu.
Myth: “Healthy children don't need the flu vaccine”
Fact: Healthy children are frequently hospitalized with flu complications. Children under 5 (especially under 2) are at high risk for serious complications. During typical flu seasons, approximately 20,000 children under 5 are hospitalized and 100-200 children die from flu-related causes in the US.
Myth: “The flu vaccine isn't effective so why bother”
Fact: Even in seasons with lower effectiveness, the vaccine significantly reduces severe outcomes. A CDC study found that flu vaccination reduced children's risk of flu-related ICU admission by 74%. Partial protection is far better than no protection.
Frequently asked questions
Why does my baby need the flu shot every year?
When should my baby get the flu shot?
Can my 6-month-old get the nasal spray instead?
What if my child has an egg allergy?
Sources
All content follows our editorial policy and is reviewed against published clinical guidelines.
2,705 evidence-based guides6 authoritative medical sources
Bottom line
The Influenza (Flu) Vaccine (IIV/LAIV) is safe, well-studied, and recommended by the CDC, AAP, and WHO. Talk to your pediatrician if you have questions about timing or your child's specific health needs.
Choosing to vaccinate your child is one of the most important things you can do to protect their health. If you have concerns, your pediatrician is always happy to talk through them with you.