Tiêm vắc-xin cúm có bị cúm không? 5 câu hỏi về vắc-xin được giải đáp

Winter is coming, and with the cold weather comes respiratory viral infections, including influenza.

So now’s a good time to protect yourself and others with the flu vaccine. It’s effective, free and widely available for many high-risk groups. Even if you don’t qualify for a free vaccine, it’s still recommended for you and your family.

Here are five common questions you might have about the flu and the flu vaccine, and our answers.

1. Is the flu really so bad?

Most flu infections are relatively mild and uncomplicated – but not all. Experimental studies, where volunteers are infected with the flu virus or rhinovirus (a cause of the common cold) , show the flu is associated with more intense symptoms that last longer.

The flu weakens the natural defences of the lung. This can allow bacterial or fungal infection to become established, leading to secondary pneumonia.

The flu is also thought to trigger heart attacks, stroke and other cardiovascular disease. In young children, it can trigger febrile seizures (childhood seizures caused by a sudden spike in body temperature) .

Uncommonly, the flu virus can directly infect body organs other than the lungs, leading to often severe and devastating diseases. These include infection of the brain (causing encephalitis) or heart (myocarditis) .

Frail, older people may have a limited capacity to cope with the stress of infection. So for them, the flu can trigger confusion (delirium) , dehydration and cause other body systems to fail.

The groups with the highest risk of flu-related hospitalisation are at each end of the age spectrum – young infants and children, and older people, particularly those with other chronic (long-term) illnesses.

The flu is associated with some of the highest rates of hospitalisation compared with other common respiratory viruses, in children and adults.

In 2025, Australia had an estimated 1,744 deaths involving the flu.

2. Do kids really need a flu vaccine?

Of half a million flu cases diagnosed in Australia in 2025, about two in five were diagnosed in those under 18 years. This results in thousands of children admitted to hospital with the flu each year.

Although children with underlying health conditions are more likely to develop complicated influenza, over half of hospitalised cases occur in healthy children.

According to one study, flu was involved in at least 29 children’s deaths in Australia in 2018–23, mostly as a direct cause. Around half of these children were healthy before they contracted the flu.

Two out of three Australian children will avoid a flu infection or flu-related complications with a flu vaccine. That’s a vaccine effectiveness of about 65%.

So a flu vaccine is recommended, every year for every Australian child from six months of age.

3. Does the flu vaccine give you the flu?

There are two types of flu vaccine.

Injectable flu vaccines

Injectable flu vaccines do not contain the flu virus, so cannot give you the flu. These vaccines contain purified haemagglutinin, a protein present on the surface of the flu virus. When you receive this vaccine, your immune system is “primed” to recognise it in the future, should it encounter the flu virus.

Common symptoms after this type of flu vaccine include pain at the injection site, fatigue, headache, muscle and joint pain. These symptoms can easily be mistaken for the flu, but they’re actually your body’s response to the haemagglutinin.

Nasal spray vaccine

This year, the flu vaccine delivered as a nasal spray (FluMist) became available in Australia. It’s registered for use in children 2–17 years, and is available for free in some jurisdictions for certain age groups.

This is what’s called a live-attenuated vaccine. It contains a weakened “live” form of the flu strain that replicates only in the nose rather than deeper inside the body.

After administration, more than half of children will have a blocked or runny nose, and around one in ten have a fever or headache. This occurs as the immune system responds locally, in the nose, to the weakened “live” flu strain.

FluMist does not lead to infection of the lungs and lower airways. So it cannot cause the serious illness or complications we can see with a normal flu infection.

4. Can the flu vaccine ‘overwhelm’ your immune system?

Flu vaccines work by training the immune system on antigens – small, harmless components of the virus.

We are exposed to hundreds of different antigens every day. For example, one study found healthy humans have demonstrable immune responses to hundreds of antigens in food. We are also constantly exposed to antigens on our skin and in our gut, and through natural infection. So a small dose of a few antigens in a flu vaccine is not able to “overload” or “overwhelm” the immune system.

We routinely combine vaccines and vaccination. Sometimes that’s in a combination vaccine such as the combined diphtheria-tetanus-whooping cough vaccine or by administering more than one vaccine at a time. Our routine national childhood immunisation schedule usually recommends between two and four vaccines at a time. For adults, it’s recommended to have your flu vaccine at the same time as a COVID booster or the new vaccine against RSV (respiratory syncytial virus) .

There’s no evidence any of these methods “overload” or “overwhelm” your immune system.

5. Is the flu vaccine safe if I’m pregnant?

Pregnant women, their unborn babies and newborns are at high risk of flu complications. So women are recommended a flu vaccine at any stage of their pregnancy.

Studies have examined the safety of flu vaccines in pregnancy. One systematic review compiled results from 40 studies. It found no evidence the injectable flu vaccine was associated with birth defects or stillbirth. Flu vaccines were however associated with lower rates of preterm birth and low birthweight.

Flu vaccines are not generally effective in infants younger than six months. But antibodies transfer from the mother to the baby via the placenta following immunisation, providing protection against infection.

An injectable flu vaccine in pregnancy provides protection to pregnant women, their unborn infant and their newborn baby.

Chris Blyth receives funding from the Australian Department of Health, Disability and Ageing, and the Australian Centre for Disease Control. His institution receives funding from Astra-Zeneca for vaccine-related research. He is a member of the Communicable Disease Network of Australia, the West Australian Immunisation Advisory Committee and a former member of the Australian Technical Advisory Group on Immunisation. He is president-elect of the Australasian Society for Infectious Diseases.

Allen Cheng receives funding from the Australian Centre for Disease Control and the National Health and Medical Research Council for studies of respiratory virus infection. He was a member of the Australian Technical Advisory Group on Immunisation.