Prof Wendy Barclay
Swine flu is making headlines all over the world. It's also making lots of people worried about what might happen next.
So what is the truth about swine flu?
We put YOUR questions to Professor Wendy Barclay from Imperial College London.
How did swine flu start? - Eleanor, 9, Scarborough
Swine flu started in Mexico when a virus in pigs managed to infect a person.
We think that two different types of viruses combined together in the pigs to create something that didn't exist before now, and that is why it has happened today and not before now.
This sort of thing happens all the time in nature when different viruses combine together, and sometimes the new virus can infect people, but most times it doesn't.
What causes swine flu? - Natalie, 10, Nottingham
Swine flu is caused by a virus. Viruses are tiny, so small you can't even see them in a normal microscope. They cause illnesses we know about like colds, measles and chicken pox.
The virus that causes swine flu is really similar to the virus that causes the type of flu people get every winter, that we call 'human flu'.
What are the signs of swine flu and how can you avoid it? - Sam, 10, Knottingley
Swine flu causes symptoms just like any ordinary flu that affects people each winter. You get a cold, and perhaps a sore throat. You might feel hot or have a headache or generally feel a bit achy or tired. It only lasts a few days.
The chances that you would catch the swine flu virus will be lower if you wash your hands plenty of times each day with soap and water and don't touch your face.
Can you get swine flu if you haven't been to Mexico? - Rebecca, 13, Lowestoft
So far most of the people who have got swine flu caught it while they were on holiday in Mexico because there is a lot of the virus there at the moment.
It may be that in a few weeks, as the virus spreads, people will catch swine flu from other people in this country, but right now there is only a very small chance of that.
People are now catching swine flu from people who've not been to Mexico
Why is it so difficult to contain the outbreak of the flu? - Isobel, 13, Kings Lynn
Flu is spread between people through the air. Because we all share the same air that we breathe, it can spread quite easily.
Also because sometimes people who have the virus don't feel very ill until a few days after they caught it, they can pass it onto other people without knowing.
If we do get it how easy is it to rid of? Also how prepared is the UK? - James, 12, Preston
When you get infected with flu virus, it only stays in your body for a few days before your own immune system fights off the virus and kills it.
The difficult bit is that during that time you might have passed it on to the next person - that is how the virus survives, by going from person to person.
We are more prepared in the UK than most countries in the world, and more prepared than ever before to deal with a new flu pandemic (a widespread outbreak of the disease).
We have some antiviral drugs that people can take, that combined with the help of their own immune systems will mean they can fight off the virus. There are lots of plans in place to deal with the outbreaks.
Why is there no vaccination for it already? If you you've already had the normal flu jab, would you still be affected by swine flu? - Ruth, 10, Northern Ireland
We don't think that the normal flu vaccine will work against this particular strain of the virus because it does not look exactly like what has been going around in people up until now.
We need to make a special vaccine for this virus, and work has started on that already. It might take a few months but should be ready before the autumn when we really need it.
Is it safe to travel by plane anywhere around the world - not just Mexico - during this outbreak? And if it is not entirely safe, what can we do to protect ourselves while travelling? - Suzanne, 13, Herts
It is safe to travel in planes. But just like everywhere else we can help protect ourselves against picking up the virus in a crowded place by washing our hands with soap and water a lot, and not touching our face too much.
Hopefully if people are coughing or sneezing they will do it into a tissue and then throw the tissue away.
How many people are expected to get swine flu? What areas will be most affected? - Ellie, 13, Wilkinson
It is difficult to say right now whether the new virus will really spread everywhere, but that is possible. We might find that half of us get infected by the virus eventually in the coming years, but most people won't even know they have had it.
In busy cities like London the virus might spread around faster, but these days when people travel such a lot, even people who live in small villages could come into contact with an infected person and catch it.
It might be that in the UK most people won't catch the virus until next autumn when the weather gets colder, because that is when viruses usually spread around more.
I don't know anyone with swine flu but loads of people at my school are freaking out - they say it is expected that 5m people will die in Britain, is this true? - Isabella, 13, Warwickshire
No I think this is extremely unlikely. From what we can see right now, even if many people got infected with the new virus, most people would have only a mild cold.
Only a tiny proportion of those who caught the virus will die, and actually people do die from normal human flu every year and we don't think that swine flu will be much different.
One of my friends said that if swine flu gets out of hand and infects a lot of people in the UK then flu jabs will be taken to schools and given to children the jabs. Is this true? - Chloe, 13, Banwell
Giving people a vaccine against a virus like flu is the best way to protect them. We hope that in the next few months a vaccine to protect us against swine flu will be made.
Once that happens people will be asked whether they want the vaccine, and giving it out in schools might be one way to get it to children quickly.
Swine flu is a pandemic on level 5 so does this mean it is this going to kill a lot of people in the UK? - Lauren, 12, Essex
The pandemic alert level 5 means that the World Health Organization think it is quite likely that this virus will spread around the world and affect a lot of different countries.
But most people will only have a mild cold if they catch the virus and only a tiny proportion of them will get more sick that that or even die.
I have been poorly for the last week with what my mum thinks is a bad cold or flu but I'm worried that I may have swine flu - how do I know if I have it or not? - Lorah, 12, Middlesbrough
Right now the only people in the UK that have swine flu are the people that went on holiday to Mexico and caught it there. So it is really unlikely that you actually have swine flu.
We all get colds and flu sometimes, and you have most likely just caught a normal cold virus. But the symptoms you have are not unlike what you might get if you had swine flu, and you will get better in the next few days, I am sure.