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We asked for your questions about the flu sweeping the country; The Globe's health reporter André Picard found answers.  (Have a question? Submit it in the form below.)

What's the difference between norovirus and the flu – or are they the same? Wayne, St. Thomas, Ont.

Influenza is a virus and norovirus is a virus but otherwise they are very different. The flu is a respiratory illness – it attacks the lungs, causing you to cough and have trouble breathing. Norovirus – also known as vomiting disease – attacks the gut and causes you to, well, you probably guessed by the name. The main reason hospitals are overwhelmed this winter is because both flu and norovirus have hit simultaneously. There is a vaccine to protect against the flu, but not one to protect against norovirus.

How can you distinguish flu and food poisoning? – Brian, Bowmanville, Ont.

Typical symptoms of food poisoning are nausea, vomiting, abdominal cramping and diarrhea that come on quite suddenly. Typical influenza symptoms are fever, cough and chills, which come on suddenly. So they are very different. What is more difficult is distinguishing food poisoning from norovirus. That's because you can catch norovirus from contaminated food or water, as well as from other people.

I think I have the flu; my husband says it's just a bad cold. How can I tell them apart? – Alice, Mississauga, Ont.

It's all about severity of symptoms. A cold will cause sneezing, a stuffy or runny nose, sore throat and hacking, phlegmatic cough. With influenza you will usually have a fever, muscle aches and chills, and the cough is dry. Both are unpleasant and the treatment is the same: rest and drink plenty of fluids.

I got a flu shot but now I have horrible stomach flu. Why didn't the vaccine work? Tracy, Calgary

The flu vaccine protects against infection with three strains of influenza. (One of those strains, H3N2, is the one that is making many Canadians sick.) However, there are many other viruses and bacteria that circulate in the winter and the vaccine will not protect against those. Influenza does not normally cause stomach problems in adults (it can in children) so it is unlikely you have the flu. The term "stomach flu" is a misnomer but it's often used to describe gastrointestinal illnesses like norovirus, which is circulating widely this year, particularly in Western Canada. So your flu shot may well have worked, but another type of bug made you sick.

Should I give my four-year-old and two-year old the flu shot? Does it really work on young children? – Cindy, Markham

The National Advisory Committee on Immunization recommends that all Canadian over the age of six months get the flu shot. The traditional flu shot works for children, but a nasal version of the vaccination is even more effective for kids. (The nasal spray is not yet available in all jurisdictions.) What is important to remember is that influenza is particularly dangerous for children under the age of five because they are susceptible to pneumonia (a life-threatening inflammation of the lungs). Hundreds of young children are hospitalized with influenza in Canada each year – last week alone 69 Canadian children were hospitalized with severe flu symptoms – and there are, sadly, a handful of deaths. That is why some infectious disease specialists are lobbying for annual, school-based flu vaccination programs.

Can I still get the flu if I've had the flu shot? Raymond, Richmond, B.C .

Yes you can still get the flu if you've had the flu shot. The vaccine protects against three strains, but there are others circulating. In addition, even when the vaccine is a match, it does not confer 100 per cent protection. Dr. Thomas Frieden, director of the U.S. Center for Disease Control and Prevention, said Friday that the current vaccine is 62 per cent effective against current strains. That is quite different from basic childhood vaccines, which are more than 90 per cent effective. Without wading too deeply into the science, there are a couple of reasons for this: 1) it take a couple of weeks for the flu vaccine to create an antibody response and people remain susceptible in that time and 2) people don't always mount a strong response to the vaccine, particularly if they have a compromised immune system.

What is most unfortunate is that the vaccine is least effective in those who most need it – the frail elderly, young children and others without robust immune systems. "The flu vaccine is far from perfect but it's still by far the best tool we have to prevent the flu," Dr. Frieden said. But there is no question better flu vaccines are needed.

I've had the flu before so there's no point getting a flu shot right? – Ashok, Burnaby, B.C.

Getting the flu and recovering will confer natural immunity – but only for that particular strain. So, if you contracted the widely circulating strain of the flu this year, A/Victoria (H3N2), there is probably not a lot of point getting a flu shot now. It should be noted however that, after the A type of the flu hits, there is usually another wave of B type flu that follows a few weeks later so you could, theoretically, get the flu again. And, next year, there will be new strains of the flu circulating so you will need a vaccine to protect you against those. You are unlikely to have much natural immunity.

I read online that the flu is now officially an epidemic. That sounds bad. What does it mean? – Marnie, Saskatoon

The term "epidemic" conjures up visions of horror and mass destruction. But here's the official CDC definition: "The occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time." The flu, for example, is considered to have reached epidemic levels when it accounts for more than 7.7 per cent of deaths in a given week. That threshold was crossed Friday in the U.S. At the same time, data suggests that the spread of the flu has peaked and it is beginning to wane.

Is the flu and its impact actually getting worse, or is there just a greater amount of media coverage this year? Laura, Scarborough, Ont.

Though terms like "Flumaggedon" are being tossed around and we are officially in an epidemic now, the reality is that this is a moderate flu season so far. There is no perfect tool for measuring the severity of a flu season but the best measure comes from the CDC, which tracks what percentage of people who see a healthcare provider do so because of an influenza-like illness (ILI). Over the past four weeks, that number has risen to 5.6 per cent from 2.8 per cent. Last year – a mild flu season – that figure peaked at 2.2 per cent. During the 2009 H1N1 pandemic, the ILI hit 7.7 per cent. And back in 2004, the last time there was a severe flu season, the ILI peaked at 7.6 per cent.

In Canada, we simply don't do a very good job of tracking the flu with hard numbers but, anecdotally, the consensus seems to be this is the worst 'normal' winter in memory (the 2009 pandemic being an exceptional circumstance) in hospitals. But this is due not to influenza alone, but to the simultaneous and early outbreaks of flu, norovirus and respiratory syncytial virus (RSV) in children. So, to answer your question: Yes, the flu is getting a disproportionate amount of media attention this year, particularly with the echo chamber effect created by increasingly popular social media. But, overall, the impact of respiratory viruses is probably not getting adequate coverage.

Is there anything that can be done to shorten the flu's duration?Paul Tate, Milton, Ont.

Flu symptoms – fever, cough, muscle ache – tend to come on quickly and last five to 10 days. The best treatment is rest, to let your immune system concentrate on the task at hand. Drinking plenty of fluids is important to avoid dehydration. To shorten the duration and intensity of your suffering, you have to treat the symptoms. In studies, antiviral drugs – Tamiflu and Relenza – lessened duration by about one day on average, but they are prescription drugs that have to be taken immediately after onset and the evidence that they make a marked difference in the real world is pretty weak. Pain relievers like acetaminophen (Tylenol) and acetylsalicylic acid (ASA or Aspirin) can ease fever and muscle ache. But use them carefully. Never give ASA to children because it can lead to Reye's s syndrome, a rare but serious illness affecting the brain and liver. And be aware you can overdose on Tylenol and suffer grave liver damage. Hot water bottles and warm baths are pleasant, safe treatments for muscle pain. Many flu sufferers like to use a humidifier or gargle warm water to ease their cough. Cough syrup is largely ineffective; hot herbal tea with honey or chicken soup works just as well for a throat tickle. Again, never give non-prescription cough syrup to children, it can suppress breathing. Some physicians recommend avoiding caffeinated beverages because caffeine is a diuretic. In short, though, time is the best healer.

If you get the flu, how do you know if you should see a doctor or just let the virus run its course at home? – Tanya, Montreal

The flu is unpleasant but most people don't need to see a doctor or go to the emergency room. There is not much health professionals can do for you other than tell you to rest and drink plenty of fluids. However, influenza can, in some cases, cause pneumonia (inflammation of the lungs) and severe dehydration, both potentially life-threatening conditions so you have to aware of your symptoms worsening rather than lessening over time. An adult with the flu who suffers significant shortness of breath, chest pain, sudden severe dizziness or persistent vomiting should see a doctor immediately. In high-risk flu sufferers – meaning babies, frail elderly, people with lung diseases like asthma, or the immune-compromised – signs of labored breathing, bluish skin colour, fever with rash, or severe lethargy should be treated as a medical emergency.

I've heard that some people have a type of flu cough that lasts 100 days. Is that true? Harriet, Toronto

"100-day cough" is a common nickname for pertussis, also known as whooping cough. Pertussis is a bacterial infection; influenza is a viral infection. They are not the same thing. However, there are currently large outbreaks of pertussis in some regions of Canada and the U.S. occurring simultaneously to flu outbreaks and that has caused some confusion. The one thing that the flu and whooping cough do have in common though is they are both vaccine-preventable illnesses.

What happened to the pandemic flu that we heard so much about in 2009? - Marcie, Halifax

A pandemic flu is a strain that has never been seen before, meaning no one has natural immunity. The pandemic flu, formally called A/California (H1N1), came and went and it is now a 'normal' flu. In fact, there is still a little bit of H1N1 circulating in Canada. But the dominant strain, the one that is making most people sick, is A/Victoria (H3N2).