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Six questions about cold and flu

What’s the difference between cold and flu, how do you best treat them, and how can you avoid getting ill this winter?

Consultant virologist and Naked Scientist, Dr Chris Smith, busts a few myths.

Click here to listen to the full interview with Dr Chris and Phil Williams on BBC Radio 5 Live.

(Photo: Getty Images)

What’s the difference between cold and flu, and does the £20 note test work?

Dr Chris Smith explains the £20 note test, which he says is a good one for deciding if it's flu: “The whole point is that if you say to someone 'there’s a high value item, (like a £20 note), and it’s just within easy walking distance...go and get it and you can have it'.

"People who have flu will say ‘you know what, you can keep it, because I just feel so bad’. That’s the sign of the flu.

"If you can’t get out of bed, you ache all over, have a high fever, you’re absolutely exhausted, have a runny nose, sore eyes and a bit of a cough, that’s usually the flu.”

Can a cold lead to the flu?

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“No, these are quite different entities,” says Dr Smith.

“The flu and a cold are viruses. Viruses are tiny particles that are the ultimate parasite. They’re so tiny that they are regarded as an infectious bag of genes; they’re just genetic information.

"They need to invade a cell, like the cells in your nose and throat, in order to grow.

"There are lots of different types of virus, they fall into different families. The flu is an entirely different family of viruses. The posh word for them is the Orthomyxoviruses and their origin is birds.

"Certain types of viruses mutate their genetic information so they’re getting a kind of molecular facelift as they go, so you can even catch them again because they look totally different when they come back to get you the next time. That’s what flu does.”

Can nasal sprays help stop a cold if you use them during early symptoms?

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There is some clinical data supporting their use, but how do they work? Dr Smith says one of the ways is by creating a barrier over the surfaces of cells.

You need very few virus particles to get infected with flu."

“This prevents the sort of things that are trying to cling to those cells, flu viruses and so on, from getting a good foothold. It’s a bit like anatomical Teflon.

"It’s a temporary barrier which means the agents can’t cling on, they can’t infect as effectively as they would when that stuff if there."

But, as he explains, we’re mostly fighting a losing battle;

“Looking at the numbers, you need very few virus particles to get infected with flu. These particles are 100 nanometres, (or one ten thousandth of a millimetre), across for a flu virus and someone infected with the flu is sneezing out thousands and thousands of flu virus particles with every sneeze.

"So there is some clinical data supporting the use of some of these sprays, but these viruses have become very, very good, over millions of years of evolution, at infecting us.”

Does the flu jab work?

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"Although people have disparaging things to say about flu jabs,” Dr Smith says,“actually the evidence is they’re really, really effective.

Although people have disparaging things to say about flu jabs, actually the evidence is they’re really, really effective."

"If you ask the people who make the flu vaccine, who have all the data, they’ll tell you it’s about 75% effective. Last year the flu vaccine wasn’t as effective.

"But what actually was wrong with it is that one of the components didn’t work as well. The reason it doesn’t work as well is that at the moment making the flu vaccine is based on an element of prediction and guess work.”

Dr Smith points out that there is work being done by the World Health Organisation to improve the process:

“They've got hundreds of laboratories around the world where every year they test 20,000 samples of flu that are collected from around the world.

"They take them and compare what’s in the vaccine with what the virus is doing in the countries which are currently conflicted with flu. If there are mismatches the people who advise on what goes into the vaccine suggest that they update the vaccine, and they change it.”

Is it true that by the time you’re experiencing the symptoms of a cold or flu you are no longer infectious?

(Photo: PA)

"There are certainly some virus infections which are no longer infectious by the time you’ve got the symptoms", says Dr Chris Smith.

“But the vast majority of cough and cold viruses will make you have the symptoms of sneezing and coughing and running eyes because that’s the virus triggering you to cough and sneeze and splutter and spray that virus out into the environment.

"So people are usually at their most infectious with a cold when they’ve got the worst symptoms. When someone ceases to be symptomatic, that’s when the infection risk has dropped much, much lower.

"So steer clear of people who are coughing and sneezing.”

Why is it that doctors will often tell you that you can’t have antibiotics for a cold?

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Dr Smith says: “A virus is not a living entity like a bacterium. When it goes into one of your cells, the genetic information hijacks the cell and it uses all of your own cells machinery to make more viruses. This means that it’s very difficult to make drugs that will exploit differences between the virus and your own cells to stop it.

Treat a common cold with common sense, not antibiotics."

"That’s why we have very few anti-viral drugs at the moment. On the other hand, bacterial cells are a living, viable, organism and are very different in structure to our own cells. That means we can make drugs that exploit the differences between a bacterial cell and our own cells. That’s how antibiotics work.

Dr Smith explains that 80 to 90% of the time when we have cold or flu symptoms it’s a virus infection.

"Treat a common cold with common sense, not antibiotics. The best thing you can do is take it easy for a few days, take things like paracetamol (in the correct dose and only if you’re not allergic), and eat plenty so your immune system can make loads of cells and antibodies.

"It’ll get rid of the virus, make you immune and then you’ll be better and bounce back quickly. If you’re not better after a few days then ring the doctor.”

NHS Choices has more information on cold and flu care.