How Effective Is the Flu Vaccine?
How Effective Is the Flu Vaccine?
Influenza vaccination is widely recommended as a preventive measure against seasonal influenza infection. However, many individuals want to understand how effective the vaccine is before deciding whether to take it. Vaccine effectiveness varies from year to year because influenza viruses change frequently and vaccine formulations are updated accordingly.
Definition: Flu Vaccine Effectiveness
Flu vaccine effectiveness refers to how well the influenza vaccine reduces the risk of influenza infection or related complications in vaccinated individuals compared with those who are unvaccinated. Effectiveness depends on factors such as vaccine strain match, individual immune response, and circulating virus types. Protection may include reduced infection risk as well as reduced illness severity.
The Short Answer
In most years, the flu vaccine reduces your risk of getting flu by about 40–60%. That means if 100 unvaccinated people catch flu in a given season, vaccination would prevent it in roughly 40 to 60 of them. In well-matched years, protection can reach 70%. In poorly matched years, it may be closer to 20–30%. But even then, vaccination still reduces the chance of serious illness.
What Does "Effectiveness" Mean?
Vaccine effectiveness (VE) is a percentage that tells us how much less likely vaccinated people are to get flu compared to unvaccinated people. It is measured in real-world conditions each season, after the vaccine has been given to millions of people.
A VE of 50% means vaccinated people are half as likely to get flu as unvaccinated people.
How Much Protection Can You Expect?
Against getting flu at all:
Season type | Approximate protection |
|---|---|
Well-matched year | 60-70% |
Average year | 40-60% |
Poorly matched year | 20-30% |
Against serious illness and hospitalisation:
This is where vaccination tends to perform best. Even in poorly matched years, the vaccine significantly reduces the risk of severe outcomes:
Outcome | Approximate reduction in risk |
|---|---|
Hospitalisation (adults) | 40-60% |
Hospitalisation (adults 65+) | 40-70% |
Hospitalisation (children) | 50-65% |
ICU admission | 50-82% |
Flu-associated pneumonia | 30-50% |
Flu-related death (older adults) | 48-65% |
These figures come from observational studies and vary by season, age group, and how well the vaccine matches circulating strains. They are reasonable estimates rather than fixed values.
Vaccination works better against severe outcomes than against mild infection. Even in years with a weaker match, the vaccine significantly lowers the risk of being admitted to hospital, needing intensive care, or dying from flu-related complications. Studies show flu-related hospitalisation risk in older adults is reduced by roughly 40–70% in good seasons — and protection against death is meaningful even when protection against infection is modest.
One important note: vaccinated people who do still get flu tend to have milder symptoms, shorter illness, and lower risk of complications — so the vaccine provides a degree of protection even when it does not fully prevent infection. This is why public health authorities continue to recommend annual vaccination even during seasons with imperfect strain matching.
Why Does Effectiveness Vary So Much?
Three main factors determine how well the vaccine works in any given year:
- Strain match. The flu virus changes every year. WHO scientists predict which strains will circulate and update the vaccine accordingly. If the prediction is accurate, effectiveness is higher. If the virus drifts unexpectedly, it is lower.
- Age and immune response. Younger, healthier adults generally mount a stronger immune response. Older adults and immunocompromised individuals may produce fewer antibodies, but still benefit significantly — especially against severe disease.
- Waning immunity. Protection gradually declines after vaccination. This is one reason annual vaccination is recommended — it keeps your antibody levels high during the season when you need them most.
What Happens If You Still Get Flu After Vaccination?
Studies consistently show that vaccinated people who do get flu tend to have milder symptoms, shorter illness, and lower risk of complications such as pneumonia or needing hospital care. The vaccine still provides meaningful protection even when it does not fully prevent infection.
Who Should Consider Flu Vaccination?
Annual flu vaccination is generally recommended for:
- Adults aged 65 years and above
- Children aged 6 months and older
- Pregnant women
- Individuals with chronic medical conditions (e.g. asthma, diabetes, heart disease)
- Immunocompromised individuals
- Healthcare workers and caregivers
- Residents of nursing homes or long-term care facilities
- Individuals who travel frequently, particularly to countries with winter flu seasons
These groups may have higher risk of complications if infected.
Who May Not Need It?
Some individuals may not require vaccination immediately:
- Healthy adults with low exposure risk
- Individuals who have already received the current season’s flu vaccine
- Those with documented severe allergy to a vaccine component (requires medical review)
Even among lower-risk individuals, vaccination may still be considered for preventive reasons.
Limitations and Risks
Flu vaccination has several limitations:
- Effectiveness varies depending on how closely the vaccine matches circulating strains
- Protection decreases gradually over time
- Vaccination does not protect against non-influenza respiratory viruses
- It does not treat an active influenza infection
Possible side effects include:
- Injection site pain or redness
- Mild fever or fatigue
- Headache or muscle aches
- Rare allergic reactions
How Much Does It Cost in Singapore?
In Singapore, flu vaccination typically costs:
- $30 to $50 per dose at private GP clinics, $32 at Minmed Clinics islandwide
- Subsidies may be available for eligible individuals under CHAS
Prices vary based on vaccine type and clinic setting.
Frequently Asked Questions
Do I need fasting before flu vaccination?
No fasting is required. Individuals can eat and drink normally before the appointment.
Is flu vaccination safe?
Flu vaccines are generally well tolerated. Mild side effects such as arm soreness, fatigue, or low-grade fever may occur. Serious allergic reactions are rare but can occur.
How often should I receive the flu vaccine?
Flu vaccination is typically recommended once every 12 months. This is because immunity decreases over time and influenza virus strains change each year.
Is flu vaccination suitable for younger adults?
Healthy younger adults may still consider vaccination, especially if they work in high-exposure environments or live with vulnerable individuals. Suitability can be assessed during a medical consultation.
Can the vaccine still work if the virus changes?
Yes, but effectiveness may vary depending on how closely the vaccine strains match circulating viruses. Even when the match is imperfect, vaccination may still reduce illness severity and complications.
Does the flu vaccine prevent all respiratory infections?
No. Influenza vaccination specifically protects against influenza viruses. Other respiratory viruses such as rhinovirus, adenovirus, COVID19, RSV or coronavirus are not prevented by the flu vaccine.
If you are considering flu vaccination, services are available at Minmed Clinics. Speak to our doctors to understand which option is suitable for you or loved ones.
🔗 Find out more about flu vaccination services
Medical Review & Authorship
This page is medically reviewed by:
Dr Yap Jun Jie Julian
MBBS, GDFM
Minmed Group Medical Doctor
The information provided is for general educational purposes and does not replace an individual medical consultation.
Last updated: May 2026