Why does the flu vaccine have to be given every year?

Two reasons. The circulating strains change from season to season, so the vaccine is reformulated each year to match them. Protection also fades over several months, so last season’s dose does not reliably cover this season.

Why do some children need two doses in their first year of vaccination?

A child meeting the flu vaccine for the first time, usually under nine years old, often needs two doses about four weeks apart to build a full response. In later seasons a single annual dose is enough.

Can the flu vaccine give my child flu?

No. The injected vaccine contains no live virus, and the nasal spray uses a weakened strain that cannot cause flu illness. A mild fever or achiness for a day afterwards is the immune system responding, not an infection.

Disease

Influenza

A viral infection of the airways that returns every year and hits young children hard.

Reviewed by TinyDose editorial teamLast reviewed June 2026

What it is

A viral infection of the airways that returns every year and hits young children hard.

Main symptom

Fever that comes on suddenly, often high

How it spreads

Spreads through droplets from coughs and sneezes, and by touching surfaces the virus has landed on and then the face.

Prevented by

Influenza

Influenza, or flu, is a viral infection of the nose, throat and lungs. It is not the same as a common cold: flu tends to arrive suddenly, with fever and body aches, and it can put young children in hospital. The virus changes slightly each year, which is why the vaccine is updated annually and given every season rather than once for life. Children under five, and especially under two, are among the groups most likely to need hospital care.

Symptoms

Fever that comes on suddenly, often high
Cough and sore throat
Body aches, headache and marked tiredness
Runny or blocked nose
In babies, poor feeding, unusual sleepiness or irritability

How it spreads

Spreads through droplets from coughs and sneezes, and by touching surfaces the virus has landed on and then the face.

Incubation1-4 days

Why it's serious

Most healthy children recover at home in about a week. The reason flu is taken seriously in this age group is not how common severe illness is, but how quickly it can develop in a baby who was well that morning.

Pneumonia, the most common serious complication
Ear infections and sinus infections
Worsening of asthma or other long-term conditions
Febrile seizures in young children
Dehydration from poor feeding during the illness

Most at risk: Children under five, and particularly under two, along with children who have asthma, heart or lung conditions, diabetes or a weakened immune system.

How to prevent Influenza

Vaccination is the most effective protection. Influenza is prevented by:

VaccineInfluenzaAn annual vaccine against flu, reformulated each year to match circulating strains.About the Influenza vaccine →

Treatment

Care is usually rest and fluids, with attention to fever and feeding. Antiviral medicines exist and are most useful when started early in children at higher risk. A doctor decides whether they are needed.

Common questions

Sources

Influenza vaccines: WHO position paper · WHO, 2022.
Influenza (Flu) in Children · CDC, 2026.

Information on this page is compiled from authoritative public health sources and written in TinyDose's own voice. It is intended for general understanding only. Always follow your pediatrician's guidance.

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This information is provided by TinyDose for general understanding only and is not medical advice. Vaccine names, ages and doses can vary by country, brand and individual circumstances. Always follow the guidance of your pediatrician or local health authority for your child’s vaccination schedule.