The flu shot – preventing flu to help keep you healthy

2nd November, 2022 • 8 min read

A bout of flu can leave you feeling feverish, achy, exhausted and generally fed up. The influenza virus attacks your nose, throat, and lungs (respiratory system), causing a sudden onset of

that can make you too sick to carry on with day-to-day life.

Flu symptoms can last from a few days up to about 2 weeks. But some people have symptoms that last longer, or get very unwell from complications.

So it’s a good idea to do what you can to avoid catching flu – and getting a flu shot is your best line of defense.

How effective is the flu shot?

Like all vaccines, the flu shot doesn’t provide 100% protection. However, even when it doesn't completely prevent flu, it can still reduce how sick you are, as well as lowering your risk of serious complications.

It’s generally more effective if you’re under 65 – some research suggests it’s about 50% to 60% effective for healthy people aged 18 to 64.

According to the Centers for Disease Control and Prevention (CDC), during 2019-2020, the flu shot prevented an estimated 7.5 million cases of flu in the US, as well as 105,000 hospitalizations and 6,300 deaths.

Despite this, currently only about half of Americans get an annual flu shot.

Who should have a flu shot?

In the US, the CDC recommends that everyone aged 6 months or older gets a flu shot every year.

In the UK, a free annual flu vaccine is offered by the NHS to all children at primary school and some other children and adults, including if you’re:

  • aged 50 or over
  • have certain health conditions
  • pregnant

The flu shot is especially important if you’re at higher risk of getting flu and complications from it, which can make you very unwell. Read about

who’s most likely to get flu or flu complications

Is there anyone who shouldn’t have a flu shot?

Most adults can have the flu vaccine, but you should avoid it if you’ve had a serious allergic reaction to a flu shot in the past.

If you’re allergic to eggs, ask your doctor about a low-egg or egg-free vaccine – some flu shots are made using eggs.

If you’re sick with a high temperature, it’s best to wait until you're better before having your flu shot.

How does the flu shot work?

Each year’s flu vaccine is designed to give protection from the 4 strains of flu that scientists have predicted will be most common that year. It can be given as a shot (injection) or a nasal spray.

When you get the vaccine, it triggers your immune system to make ‘antibodies’ – substances in your blood that protect you from the viruses included in the vaccine. The number of antibodies you have will be highest in the 1 to 2 months after you get it, then gradually decline – which is why you need a vaccine every year.

Remember, you can’t catch flu from the flu vaccine. The flu shot doesn’t contain any ‘live’ virus – only inactivated virus, or small parts of the virus. And while the nasal spray does contain live viruses, these are weakened and can’t give you flu.

Getting a flu vaccine won’t increase your risk of getting COVID-19, either.

What are the flu shot side effects?

Flu shots are very safe. Any side effects are usually mild and last for a day or 2, if you get them at all.

Side effects can include:

  • slightly raised temperature
  • muscle aches
  • sore arm where the needle went in
  • headache
  • feeling sick (nausea)
  • tiredness

If you get side effects from the flu shot, you can take a painkiller such as acetaminophen (

) or

What other women say about flu shot side effects

‘I’ve had the flu shot every year and never really feel anything afterwards, except for a sore arm sometimes. And that’s nothing compared with full-blown flu. I got flu in my 20s and it floored me for 2 weeks. I’ve never felt so awful – I couldn’t even make it out of bed to the couch.’
Lucy Whitehead, 44

When is the best time to get a flu shot?

‘The flu vaccine can take about 2 weeks to be effective after you have it, so waiting until the flu season has already started can leave you vulnerable to the virus,’ says Dr Ann Nainan, family doctor and Healthily expert. ‘So try to book your flu shot as early as possible. But even if it’s nearing the end of winter, you can still benefit from the flu shot.’

Read about

flu season
and when it starts in different countries.

Make sure you get a flu shot every year, too. As well as the fact that your antibody levels drop over time, flu viruses change (evolve) – so last year's vaccine may not protect you from this year's viruses. Scientists create new flu shots every year to keep up with adapting viruses.

How much does the flu shot cost?

In the US, the flu shot is covered by Medicare and other health insurers, including Medicaid and private health insurance plans – although they may say you have to have your shot at a specific place.

Pharmacies, doctor’s offices and clinics, grocery stores, urgent care clinics, college health centers, and some schools and workplaces all offer the flu shot. You’ll usually need to book an appointment in advance.

If you don’t have health insurance, contact your local or state health department. You can search for flu shot providers near you on the
website. The cost of a flu shot without insurance ranges from about $20 to $75.

In the UK, some people can get a free flu vaccine on the NHS (see ‘

Who should have a flu shot?
). If you’re not eligible for a free shot, you can get one at a pharmacy or supermarket, where prices range from about £10 to £17.

What is the high-dose flu shot?

A high-dose, or enhanced, flu shot contains 4 times more of the antigen (part of the flu virus), which increases your immune system’s response to the vaccine.

It’s often offered for people aged 65 and older, because your immune system gets weaker as you age, meaning you might not respond as well to the standard-dose vaccine.

In the US, the high-dose flu shot is now recommended for all over 65s.

Can you get the flu shot while pregnant?

‘If you’re pregnant, it’s very important to get the flu shot, whatever stage you’re at,’ says Dr Ann. ‘It will help protect both you and your baby, as you’ll pass on some flu antibodies, which will last for the first few months of their life.

‘Scientists have found good evidence that there’s a higher chance of getting flu complications such as

in pregnancy, especially if you’re in the later stages. There’s also a small risk that your baby could be born prematurely, have a low birth weight, or even be

‘Studies suggest that vaccination when you’re pregnant reduces your risk of respiratory problems from flu by about half, and your risk of being hospitalized by about 40%.

‘If you’re pregnant and think you might have the flu, see your doctor straight away.’

Will the flu shot prevent COVID-19?

‘COVID-19 and the flu have very similar symptoms, but the flu shot won’t prevent you from getting COVID-19,’ says Dr Ann. ‘However, you’re more likely to become seriously ill if you get flu and COVID-19 at the same time.

‘Getting your flu vaccine could reduce symptoms that might be confused with those caused by COVID-19, and can reduce how sick you get if you do catch flu. You may also be able to get a COVID-19 seasonal booster at the same time as your flu vaccine.’

What else can I do to prevent flu?

As well as getting your flu shot each year, try following these simple self-care steps to minimize your chances of catching flu.

Watch this space

Scientists are working on developing a ‘universal’ flu shot, which will be less affected by virus changes and could mean you don’t need to have a flu shot every year. So far, trials have only been carried out on mice, but a study on humans began in Maryland in June 2022.

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.