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From influenza A to zanamivir, what you need to know this flu season
Harvard Health Letters

Influenza is highly contagious. As a respiratory virus, it spreads on tiny droplets of mucus that spew into the air when you cough, sneeze or simply exhale.


Children ages 6 months to 8 years who have never had a flu shot before need two doses.


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Published: 11/10/2008 12:12 AM

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Flu update

What's new for the 2008-2009 flu season:

Lots of shots: Vaccine makers project 143 million to 146 million doses of flu vaccine will be available - an all-time high supply.

Three strains: This year's flu vaccine contains three new influenza virus strains: A/Brisbane/59/2007 (H1N1)-like virus; A/Brisbane/10/2007 (H3N2)-like virus, and B/Florida/4/2006-like virus. These three main strains are expected to cause most illness this year.

Source: National Center for Immunization and Respiratory Diseases

It's a rite of autumn. The days grow shorter, the temperature drops, footballs fly - and the flu strikes.

Influenza is so common that it's easy to dismiss this seasonal affliction as "just a virus" or "just the flu." It's true that the flu is caused by a virus and that most patients recover without specific therapy. But it's also true that thousands of Americans die from the flu each year, and millions are sick enough to miss work or school.

Meet the flu bug

Nearly all human cases are caused by human strains of the influenza A or B virus. Influenza A is the more serious. It has mastered the nasty trick of disguising itself by changing the proteins on its outer coat. Because of that, people who are immune to an old strain of the flu virus are not protected against new strains. That's why you need to get a new flu shot each year.

World traveler

Influenza is a worldwide problem. Because different strains of the virus crop up every year, new outbreaks occur annually. In most years, the new strains turn up first in Asia, and then spread around the world to the U.S. That gives American scientists a chance to spot epidemic strains and produce new vaccines before the flu bug hits home.

In the U.S., the flu season runs roughly from Thanksgiving to Easter, with most cases occurring in the dead of winter. In a typical year, up to 10 percent of us get the flu, over 200,000 people are sick enough to require hospitalization, and about 36,000 Americans die from the infection. And the toll can double during epidemics, which occur every 10 to 15 years.

How flu spreads

Influenza is highly contagious. As a respiratory virus, it spreads on tiny droplets of mucus that spew into the air when you cough, sneeze or simply exhale. People close at hand are the most likely to catch the flu, which is why the infection spreads so quickly through families, health-care facilities and other places where people live or work close to each other. The virus can also be spread by hand-to-hand contact.

Run over by a truck

Influenza hits fast. After an incubation period of just one to two days, the symptoms start abruptly. Most patients are feverish, and high temperatures in the 103 to 104 degrees F range are common. Nearly everyone has a runny nose and sore throat, but unlike ordinary colds, the flu also produces a hacking, dry cough. Muscle and joint aches can be severe. Headache, burning eyes, weakness and extreme fatigue add to the misery. In most cases, the high fever and severe distress settle down in two to five days, but the cough can linger for a week or two and the fatigue even longer.

Flu can kill

The most serious - and deadly - complication is pneumonia. Young children, senior citizens and people with chronic illnesses are at greatest risk, which is why they have the greatest need for preventive vaccinations and medical treatments.

In some cases, pneumonia is caused by the flu virus itself. It's a particularly deadly problem that begins early in the infection and progresses rapidly with a severe dry cough and shortness of breath.

Bacterial pneumonia is more common, but more treatable. It starts later, after patients seem to be on the mend. The fever returns, the cough increases and patients raise thick sputum (phlegm).

Other flu complications can include asthma attacks, ear infections, bronchitis, sinusitis, inflammation of the heart or other muscles, and inflammation of the nervous system.

Is it flu?

Most cases are diagnosed because the season is right, the virus is going around the community, and the symptoms are typical. But milder cases of the flu can resemble other respiratory infections that also strike in the winter. Consult your doctor for personal diagnosis and treatment.

Doctors usually rely on clinical findings to diagnose the flu. But if the symptoms are unusual or very severe, or if the flu has not yet turned up in the community, special tests can confirm the diagnosis. Most often, labs use a rapid test that can detect proteins from the influenza virus on a patient's nasal swab within minutes. Blood tests, chest X-rays and other studies may be needed if complications develop.

Get a shot

Labs develop new vaccines every flu season to protect against the two strains of influenza A and one strain of influenza B most likely heading our way in the fall. October and November are the ideal months to get the vaccine. Children ages 6 months to 8 years who have never been immunized need two doses, but one dose will suffice for all others.

Two types of flu vaccine are available. The nasal spray can be used only by healthy, nonpregnant individuals ages 2 to 49. The injectable vaccine can be given to nearly everyone, except people who are allergic to eggs or to the vaccine itself. Side effects are mild and uncommon, amounting to a slightly sore arm or a slight fever.

Immunization can reduce your risk of catching the flu by up to 80 percent. That's a big benefit, but nearly half the people who need protection the most don't get it. If vaccine supplies are adequate, everyone above 6 months of age should get a flu vaccine this fall.

Treating flu

Antibiotics don't work against viruses, including influenza. But while there are no medications for ordinary viruses, special prescription drugs can be used to treat or prevent the flu. Two older drugs, amantadine (Symmetrel) and rimantadine (Flumadine), have lost their effectiveness, but two new drugs remain active against most strains of influenza A and B.

Both medications target a viral enzyme called neuraminidase. Neither will cure the flu, but they can ease and shorten the illness if started within the first 24 to 36 hours of flu symptoms. Both drugs can also be used to prevent influenza in unvaccinated persons who are exposed to the infection.

Zanamivir (Relenza) is administered by inhalation from a nebulizer. It is approved for prevention in people age 5 and older and for treatment in people age 7 and older. Side effects may include wheezing, nausea and vomiting; behavioral abnormalities have also been reported. Oseltamivir (Tamiflu) is available in tablet form. It is approved for prevention and treatment in patients above 1 year of age. Side effects may include nausea and vomiting; behavioral abnormalities have also been reported.

If you get the flu and can start treatment within about 36 hours, ask your doctor about oseltamivir or zanamivir.

With or without an antiviral drug, be sure to get lots of rest and drink plenty of fluids. Acetaminophen (Tylenol and other brands) can help ease fever and aches; aspirin is also effective, but should never be used by flu patients under 18 years of age. And be sure to contact your doctor promptly if you think you're developing pneumonia or other complications that may require antibiotics or hospitalization.

The warmer, the better ... for us

The flu loves winter. In the northern hemisphere, it comes around between November and March, but in the southern hemisphere, it hits from May to September, the coldest months. In the tropics, however, there is no true flu season - and very little flu.

Many respiratory infections peak in winter, when people cluster together indoors. But for years, scientists have wondered if there is something special about the influenza virus that accounts for its striking seasonality. A 2007 study found an answer.

Using guinea pigs infected with human flu viruses, scientists in New York found that the virus is transmitted much more efficiently in a cool environment. Animals who were housed at 41 degrees F shed the virus nearly two days longer than animals housed at 68 degrees, and a temperature of 86 degrees blocked transmission of the virus altogether.

Low humidity provided another boost for the bug; the virus spread much more readily at 20 percent humidity than at 80 percent.

Next summer, before you complain about the heat and humidity, remember that it's protecting you from the flu.