7. Influenza

Influenza—commonly called “the flu”—is a viral infection of the respiratory system. It affects the lungs as well as the whole body. Most people recognize the symptoms—fever, body aches, sore throat, stuffy nose, and headache. Sometimes the flu is confused with the common cold, but even though some of the symptoms of the flu are the same as those of a cold, these are different illnesses caused by different viruses. In general, the flu is more severe. While it’s often possible to continue going about your daily activities with a cold, the flu usually causes a fever and extreme exhaustion that necessitate bed rest for a few days. Some people with gastrointestinal symptoms like nausea and vomiting call their illness “stomach flu.” However, the flu rarely causes these symptoms (they are more likely to occur in children than adults).

You get the flu by breathing in the influenza virus through the nose or mouth. When someone who has the flu coughs, sneezes, or even talks, droplets containing the virus are expelled into the air and can be breathed in by people nearby. The flu virus can also be picked up by touching a surface (such as a telephone or doorknob) that has been contaminated by someone with the flu. After touching the surface, moving your hand near your face allows the virus to be inhaled through the nose or mouth (see Box 7-1, “Practical Tips to Avoid the Flu”).

Most people who get the flu come down with it during the period from November to March (“flu season”). Children are more susceptible to getting the flu, and often spread the virus to others. Most people recover from the flu, with or without treatment, within a week or so, but the flu is unpredictable, and its severity varies from year to year.

Three Types of Flu

There are three types of influenza virus: A, B, and C. Types A and B are more common, and usually lead to more severe symptoms than type C. Type C influenza is most likely to affect children younger than the age of six. Most people develop immunity to influenza C early in life, and if they subsequently come in contact with the virus it causes only mild or no symptoms. The influenza viruses that cause more suffering and lead to flu outbreaks are types A and B. The genes of these viruses change over time, and different strains circulate each year.

Flu Symptoms

Infection with the influenza virus causes the tissues of the lining of the respiratory tract to become swollen and inflamed. The infection is in the respiratory system, but symptoms are felt throughout the body. Symptoms of the flu generally appear one to four days after becoming infected. They start abruptly and usually include fever (100°F to 102°F), body aches, weakness, and extreme exhaustion. Other common symptoms are headache and cough, and some people have a sore throat, stuffy nose, and sneezing. The fever usually subsides in two to three days, but full recovery takes about a week. Children with the flu have the same symptoms as adults, but they tend to have higher temperatures (103°F to 105°F).

The flu is diagnosed on the basis of symptoms and whether other cases of flu have been reported in the community. Laboratory tests are generally not necessary but may be done in some cases, to determine the type of influenza virus responsible for an epidemic.

Complications from Flu

Most people recover from the flu without incident. However, complications can arise in some groups. Children younger than age five, older adults, pregnant women, and people with a chronic disease (including asthma and COPD) or a weak immune system are most likely to be hospitalized, suffer complications, or die from the flu.

Having the flu can temporarily alter the immune system, making the lungs susceptible to bacterial infection. A bacterial infection in the lungs can cause pneumonia (see page 68). The flu virus itself also can cause pneumonia. Typically, pneumonia symptoms appear after flu symptoms start to go away. The sudden appearance of high fever, chest pain, and coughing that produces thick, yellow-greenish-colored mucus are signs of pneumonia. Other infections that may occur as a result of the flu include sinusitis, bronchitis, and ear infection.

People with heart disease and/or lung disease (such as COPD or asthma) can experience a worsening of their condition if they get the flu. Annual flu vaccines (see page 65) are recommended for everyone at risk for complications from the flu.

Some people who get the flu become seriously ill, and may even die, for unknown reasons. For example, during the 2009/2010 flu season the strain of the influenza virus responsible for most cases of the flu was called pandemic H1N1 (also called “swine flu”—pandemic means that it occurred over a wide geographic area, and affected a large number of people). Most people infected with this virus had only mild symptoms, but others became seriously ill and died. Many of those who died were healthy young adults, who generally have the lowest risk for serious illness and death from the flu.

The H1N1 strain reappeared in 2013/2014, but did not cause a pandemic, largely because many people had been exposed to it in 2009/2010 and developed immunity against it. Different strains dominated the 2014/2015 flu season. In particular, the H3N2 virus was particularly hard on older adults, resulting in the highest rate of flu-associated hospitalizations among people age 65 and older since 2005. The 2015/2016 flu season was relatively mild.

Treatment for Flu

Antiviral medicines are available to treat the flu, but they must be taken within the first 48 hours of becoming sick in order to be effective. They should be taken for at least five days. The antiviral drugs—oseltamivir (Tamiflu) and zanamivir (Relenza)—don’t completely cure the flu, but they may reduce the length of the illness and lessen the symptoms. One study found that zanamivir can shorten the duration of symptoms by about one day, and reduce infections that sometimes develop after the flu. The two medications have been shown to work against both influenza types A and B.

Relenza generally is not recommended for people with COPD or asthma, because studies have found that some people with these conditions develop bronchospasm (wheezing) after taking this drug. If Relenza is used by someone with COPD or asthma, a fast-acting inhaled bronchodilator must be available to immediately relieve bronchospasm.

Some flu symptoms can be treated with over-the-counter medications, but these do not treat the viral infection and will not shorten the length of illness. Aspirin can be used to bring down a fever, but it should not be used in children younger than age 18. Children and teenagers who take aspirin when they have the flu are at risk for developing Reye’s syndrome, a condition that affects the nerves. While this is an uncommon complication, it is not worth the risk. Use of acetaminophen (Tylenol) in children does not appear to be linked to Reye’s syndrome, and is therefore preferred for reducing a fever.

Decongestants and antihistamines can be used for relief of cough, stuffy nose, and other nasal symptoms. It’s also advisable to drink plenty of fluids and to rest.

Vaccination for Flu

The best defense against the flu is yearly vaccination. The ideal time to get a flu shot is in October or November, just as the flu season (November to March) is getting started, but it’s never too late—vaccination is recommended any time during the season. A recent study found that getting the flu shot in the morning may provide more protection for older adults than if it’s given later in the day (see Box 7-2, “Flu Shots in the Morning May Be More Effective”). But if the afternoon or evening is the only time you have to get vaccinated, do so—it will still be effective.

The flu vaccine consists of killed particles of the influenza virus. These particles do not cause the illness, but they prime the body to recognize the virus and to make antibodies against it. Antibodies are molecules made by white blood cells that bind to an infectious agent and render it harmless. If a vaccinated person is exposed to the influenza virus, the antibodies usually destroy the virus before symptoms appear. Once vaccinated, it takes about two weeks for these antibodies that protect against infection to develop in the body.

A higher dose version of the flu vaccine, called Fluzone High-Dose, is available for people age 65 and older. It contains four times the amount of antigen (the killed virus particles that stimulate the immune system) than the regular vaccine. This creates a stronger protective response that should be beneficial for older adults, who have a weaker immune system than younger people.

Vaccination works only if the body has created antibodies against the correct strain of the virus. Because influenza viruses constantly change over time, vaccine makers must develop new flu vaccines each summer by predicting the strain of flu expected to be most prevalent in the coming season.

Who Should Get a Flu Shot?

Everyone can benefit from getting a flu shot. The CDC recommends vaccination for everyone six months of age and older.

Most people have little or no reaction to the flu shot. A few people may develop swelling or soreness at the injection site, while a smaller number of people may experience a day or two of headache and mild fever. For people age 65 and older, Medicare covers annual flu shots, including the high-dose version. Many health insurance plans also pay for flu shots.

People who don’t like getting shots have a second option for vaccination: an influenza vaccine called FluMist, which is administered as a nasal spray. This vaccine is made with a live but weakened virus, but has been approved by the FDA only for healthy people between the ages of two and 49.

The benefits of vaccination have been demonstrated over and over. One study found that getting the seasonal flu vaccine cut flu-related hospitalizations among older adults by nearly two-thirds. Even if the flu shot doesn’t completely prevent the flu in everyone, it most likely prevents the most serious side effects of the flu.

A study found that babies born to women who get a flu shot during pregnancy are less likely to be underweight when born, and have fewer respiratory illnesses during flu season.

Who Should Not Get a Flu Shot?

Flu shots and FluMist are helpful for most people, but some people should avoid getting vaccinated. These include:

• Infants younger than six months
• People with an acute illness and fever (wait until you’re feeling better before getting vaccinated)

Special Considerations for Flu Shots

In the past, people with an allergy to eggs were advised against getting a flu shot because the flu vaccine is grown in chicken eggs. Now, people who have ever had a severe allergic reaction to eggs can get a flu vaccine called Flublok, which does not use chicken eggs in its manufacturing process. It is approved for use in adults ages 18 and older. People who get a mild allergic reaction to eggs (involving a skin rash) can get the regular flu shot, but they should inform their doctor about this allergy so that safety measures can be taken.

People who ever had Guillain-Barre syndrome (a rare disorder of the nervous system) should talk to their doctor about the flu shot. Some people who have this condition should not get a flu shot.

Vitamin D

Some research suggests that getting adequate amounts of vitamin D may strengthen the immune system and lessen your chances of getting the flu. Vitamin D is found in foods such as salmon, mackerel and tuna, and in fortified milk or juice. Most people meet their vitamin D requirement through exposure to the sun, unless they live in northern climates or are housebound. Sunlight penetrates the skin and converts a substance that naturally exists in skin into the type of vitamin D that is needed by the body as a nutrient. Just 15 minutes of exposure to the sun at its peak (between 11am and 1pm), without sunscreen, is sufficient. If that is not possible, vitamin D is also available in supplements. Note that recommended daily intake is now 1,000 international units (IUs) of vitamin D3, or cholecalciferol, which is stronger and more active than vitamin D2 (ergocalciferol).

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