Maybe you've never had flu, even when everyone you knew was going down with it. Maybe you've had flu and can't see what all the fuss was about. So when do you need to worry about flu and what can you do about it?
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How many times have you gone to see your doctor or pharmacist with a cold, a tummy bug, a sore throat, only to be told 'it's a virus'? The average adult gets about four colds a year (children get far more) and you may think flu is just another virus. You'd be wrong.
The influenza virus has been around for centuries. So have thousands of other viruses, but most of them don't cause serious complications. Some do, and we immunise children against these - for instance, before measles immunisation there were about half a million cases in the UK a year, with 1 in 20 suffering pneumonia and 1 in 1,000 getting inflammation and scarring of the brain. Before immunisation, mumps was the most common cause of meningitis in the UK.
But influenza is different for many reasons. Firstly there's a single measles and a single mumps virus, so one course of injections protects for years. But there are hundreds of different strains of influenza, and being immune to one doesn't necessarily protect you against getting another. What's more, every year the most common types of influenza virus during peak winter season change, as the virus evolves.
The flu vaccine
Every year, scientists at the World Health Organization use a scientific version of a crystal ball to predict the types of influenza virus that are going to cause infection in the next season. The annual flu vaccine is based on three (or for the children's vaccine four) of these types. It takes several months for laboratories around the world to gear up and produce the millions of injections offered, based on these strains. Sometimes the scientists get it wrong, and a strain of virus they didn't predict gets through, so the vaccine’s less effective. But on the whole, they do a pretty good job.
We get a good indication of what strain of virus is going to strike in the UK, and how many people will be infected, from what goes on in Australia, which has its winter in our spring.
Who gets which vaccine why?
Until five years ago, children were only offered immunisation against flu if they had medical conditions such as asthma or diabetes. But since 2013, the NHS has gradually been rolling out immunisation for healthy children, starting with 2 and 3 year-olds and gradually rolling out to include more age groups each year. This is partly to protect them - in pilot sites, hospital admissions for confirmed flu-related complications dropped by 93% among primary school age children compared to non-pilot sites.
This season, all children age 2-3 years and in reception and primary school years 1-5 will be offered flu immunisation. The evidence is that for them, a nasal spray containing a weakened form of the virus provides the best protection. It covers four strains of flu. Not only does it protect them, there's good evidence that it prevents flu among other vulnerable groups, courtesy of young people's 'super-spreader' status.
Adults under 65 at high risk of developing complications are being offered a quadrivalent vaccine, which protects against four strains of flu. Last year, the vaccine was not as effective as we'd hoped, partly because one of the B strains of flu, which wasn't included in the standard vaccine, wasn't covered. The quadrivalent vaccine should remedy that.
Another reason last year's flu vaccine was less effective than usual is that many over-65s didn't develop good immunity to the standard vaccine. So this year, they're being offered an 'adjuvanted vaccine' which provides better protection to over-65s, and particularly to over-75s.
You'll know if you have flu!
If you have a cold, you may feel miserable and sniffly but you can usually struggle through. Influenza is very different. You'll usually feel absolutely exhausted, have a very high temperature and ache all over, with a harsh wracking cough and headache. Regular exercise and a healthy diet can cut your risk.
Most people get over flu within a couple of weeks with no ill effects, with rest, fluids and paracetamol. But if your immune system is weakened, you're much more likely to get life-threatening complications like pneumonia. Even if you've never had flu in your life, your risk increases with age as your immune system winds down.
Who gets a free flu vaccine?
As you get older, your immune system weakens, so you're more vulnerable to severe complications from flu. That's why all over-65s are offered the vaccine even if they don't have any other medical conditions. Healthy children in the age groups above, along with any children with long-term health conditions, will also by invited.
In addition, you'll be offered the flu vaccine free on the NHS if you live in residential care home, have long-term medical conditions like diabetes, asthma or COPD, heart, kidney or liver problems (including heart failure), nervous system conditions like Parkinson's disease, multiple sclerosis or motor neurone disease or have any condition or treatment that weakens your immune system.
Carers can cut the risk of passing the infection on to someone vulnerable with a free vaccine.
And if you're pregnant, you're at much higher risk of complications that could harm you or your baby, so you'll be offered the vaccine free too.
Thanks to My Weekly where this was originally published