H1N1 flu (swine flu)

Symptoms

The symptoms of flu caused by H1N1, commonly called swine flu, are like those of other flu viruses. Flu symptoms start about 1 to 2 days after you're exposed to the virus. Symptoms tend to start quickly.

The first symptoms often include:

• Fever, but not always.
• Chills.
• Headache.
• Muscle pain.
• Loss of appetite.
• Painful or watery eyes.

Symptoms that come on over time include:

• Cough.
• Sore throat.
• Runny or stuffy nose.
• Tiredness and weakness.
• Wheezing or shortness of breath.
• Diarrhea.
• Feeling sick to the stomach or vomiting, which is more common in children than adults.

In young children, these symptoms may show up more as being fussy or irritable. Children with flu also are more likely than adults to have ear pain, feel sick to the stomach, vomit or have diarrhea.

When to see a doctor

If you're healthy and get the flu, you may not need to see a healthcare professional. But some people are at higher risk of flu complications.

Call your healthcare professional if you have flu symptoms and you're pregnant or have a chronic disease. Some examples are asthma, emphysema, diabetes or a heart condition.

If you have emergency symptoms of the flu, get medical care right away. For adults, emergency symptoms can include:

• Trouble breathing or shortness of breath.
• Chest pain.
• Signs of dehydration such as not urinating often enough.
• Dizziness that doesn't go away.
• Seizures.
• Worsening of existing medical conditions.
• Severe weakness or muscle pain.

Emergency symptoms in children can include:

• Trouble breathing.
• Pale, gray or blue-colored skin, lips or nail beds depending on skin color.
• Chest pain.
• Dehydration.
• Severe muscle pain.
• Seizures.
• Worsening of existing medical conditions.

Risk factors

Factors that may raise your risk of serious illness from H1N1 or seasonal flu complications include:

• Age. Influenza tends to have worse outcomes in children under age 2 and adults older than age 65.
• Living or working conditions. People who live or work in facilities with many other residents are more likely to get the flu. Some examples are nursing homes or military barracks. People staying in the hospital also are at higher risk.
• Weakened immune system. Cancer treatments, antirejection medicines, long-term use of steroids, organ transplant, blood cancer or HIV/AIDS can weaken the immune system. This can make it easier to catch the flu and may raise the risk of complications.
• Chronic illnesses. Chronic conditions may increase the risk of influenza complications. Examples include asthma and other lung diseases, diabetes, heart disease, and nervous system diseases. Other examples are metabolic disorders, problems with an airway, and kidney, liver or blood diseases.
• Race. Native Americans or Alaska Natives may have a higher risk of influenza complications.
• Pregnancy. Pregnant people are more likely to have influenza complications, especially in the second and third trimesters. This risk stays higher for up to two weeks after the baby is born.
• Obesity. People with a body mass index (BMI) of 40 or higher have a higher risk of flu complications.

Prevention

H1N1 flu began causing illness in humans in 2009. Now it is a strain of the seasonal flu. Seasonal flu vaccines are available in the U.S. for people age 6 months and older. Seasonal flu vaccines are often recommended for everyone who doesn't have a medical reason to avoid the vaccine. If you have an egg allergy, you can often still get a flu vaccine.

Getting a seasonal flu vaccine lowers:

• The risk of getting the flu.
• The risk of having serious illness from the flu and needing to stay in the hospital due to the flu.
• The risk of dying of the flu.

If the vaccine is given later in pregnancy, the flu vaccine helps protect a newborn from the flu too.

Each year's seasonal flu vaccine protects against the three or four influenza viruses expected to be the most common during that year's flu season.

The first time children between the ages of 6 months and 8 years get a flu vaccine, they may need two doses given at least four weeks apart. After that, they can usually receive single annual doses of the flu vaccine. Check with your child's healthcare professional.

Also, check with your healthcare team before receiving a flu vaccine if you had a serious reaction to a previous flu vaccine. People who have had Guillain-Barre syndrome also may want to check with a healthcare professional before getting the flu vaccine. If you have a cold or don't feel well, you may still be able to get a flu shot. But if you are seriously ill, check with your healthcare team to see if you should delay getting the vaccine.

The flu vaccine may be available as an injection, jet injector or a nasal spray.

Seasonal flu shots

Flu shots are usually offered based on your age. For older children and adults, the flu shot is usually given in a muscle in the arm. Younger children may get the flu shot in a thigh muscle.

Some types of flu vaccines may be limited to certain groups. High-dose flu shots and shots with an ingredient called an adjuvant that boosts immune response may help some people avoid the need for care in the hospital due to influenza. People over age 65 can get these vaccines. These vaccines also may be available to people age 18 and older who have a solid organ transplant and take medicine to weaken their immune response.

Jet injector for seasonal flu shot

In the U.S., adults younger than 65 may be able to get the flu vaccine using a device called a jet injector. Instead of a needle, this device uses a high-pressure, narrow stream of fluid to give the vaccine through the skin.

Seasonal flu nasal spray

In the U.S., a seasonal flu nasal spray is approved for people ages 2 through 49.

The nasal spray flu vaccine isn't recommended for some groups, such as:

• People who have severe asthma or are currently wheezing.
• People who had a severe allergic reaction to a flu vaccine in the past.
• Pregnant people.
• Young people who take aspirin or a medicine that has salicylate.
• People with weakened immune systems and caregivers or close contacts of people with weakened immune systems.
• Children between ages 2 to 4 years old diagnosed with asthma or wheezing in the past 12 months.
• People who recently took antiviral medicine for the flu.
• People with a cerebrospinal fluid leak or the potential for a leak, as with a cochlear implant.

Check with your healthcare team to see if you need to be cautious about getting a nasal spray flu vaccine. If you can take the nasal spray flu vaccine, you may be able to take it yourself or give it to an eligible child at home, without seeing a healthcare professional.

Treatment

If you don't have risk factors that make a serious illness more likely, treatment for seasonal flu, including H1N1, means helping you feel better. It can be helpful to rest, drink plenty of fluids, and take medicine to manage fever and headache.

If you have a long-term breathing condition, your healthcare professional may give you medicine to ease your symptoms.

Healthcare professionals may give you antiviral medicines within the first day or two after you start feeling sick. These medicines can help with your symptoms and might lower the chance of having complications. The U.S. Food and Drug Administration has approved these four antiviral drugs to treat flu:

• Oseltamivir (Tamiflu)
• Zanamivir (Relenza)
• Peramivir (Rapivab)
• Baloxavir (Xofluza)

But flu viruses can become resistant to these medicines. Because of this, healthcare professionals usually save these medicines for certain people. This includes people at high risk of complications and those who are often around others who are at high risk.

Using antiviral medicines wisely helps prevent resistance and makes sure these medicines work for the people who need them most.