One minute you feel fine; the next, your head throbs and your muscles and joints ache. You feel hot, then cold. Weak and dazed, you can only burrow in bed and cough and sneeze and sniffle for the 10 days it takes for the virus to run its course.
Influenza strikes fast and hits hard.
After it does, there's little any doctor can do to help. That is, until now.
Last month marked the debut of a new prescription drug called Relenza. Relenza has been shown to shorten the duration of the flu by an average of 1 1/2 days. In addition, the drug has been shown in clinical trials to be effective in reducing the spread of influenza among family members by as much as 79 percent.
Relenza -- generic name zanamivir -- has been approved by the U.S. Food and Drug Administration only for treatment, not prevention of the flu.
But with flu season upon us -- a few cases have already been reported in Maryland, according to the Centers for Disease Control and Prevention -- the debut of the drug is good news to anyone who fears the onset of influenza.
The sicker you are, the better Relenza works, its developers say.
"The earlier the treatment and the sicker the patients, the greater the clinical benefits," Dr. Frederick Hayden of the University of Virginia, says of Relenza. "There's no point in using it with mild fever and minimal symptoms."
In addition, Relenza reduces complications from the flu, says Hayden, who headed clinical trials of the drug. "With zanamivir there's a reduction in bronchitis and pneumonia of about 40 percent," he says.
Millions of people in the United States will get the flu this year. Some 20,000 people will die from it.
Influenza is caused by viruses that infect the respiratory tract. The two most serious types of the virus are Influenza A and B, which are spread through the air.
Flu viruses are constantly changing over time, usually by mutation. These changes enable the virus to evade the immune system of its host, so that people are susceptible to influenza virus infection throughout life.
The flu can be especially harmful to people over age 65 and to those with chronic heart, lung or kidney disease, diabetes, compromised immune systems or severe anemia. These people are at risk of developing severe complications.
Relenza is a powder that is inhaled using a hand-held breath-activated device and delivered to the surface of the lungs, the primary site of flu infection. Patients orally inhale 10 milligrams of Relenza twice a day for five days. Calls to three Baltimore area pharmacies and one online pharmacy yielded price quotes of $42 to $58 for this treatment.
Isn't that a lot of money to pay for two days of wellness? "That depends," says Hayden. "What are two days worth to you?"
Relenza belongs to a new class of compounds called neuraminidase inhibitors. Neuraminidase is an enzyme that breaks the bond holding new particles to the infected cell. Once broken, the new viruses are free to infect other cells, spreading the infection. Relenza is thought to work by inhibiting breakage of the bond and preventing release of the new viruses, therefore interrupting the spread of infection within the respiratory tract.
This is not the first drug available for fighting the flu. Two others -- amantadine and rimantadine -- are effective against influenza A, but can cause side effects ranging from stomach upset to central nervous system problems.
Oseltamivir, a new flu drug that is also a neuraminidase inhibitor, has been shown in studies to be effective in preventing and treating the flu. It was approved by the FDA in late October and will be sold under the name Tamiflu by Hoffmann-La Roche.
Relenza is the first flu medication effective against both Influenza A and B, notes Dr. Ruth Karron, associate professor of international health and pediatrics at the Johns Hopkins School of Public Health. Yet consumers should be advised that the drug is not without its shortcomings.
"It really needs to be used within the first day of being sick with the flu," Karron says.
In addition, Relenza has caused episodes of asthma in people with asthma. "What the prescription information suggests is that people with asthma use their inhalers before they take the medication and have them available afterward," Karron says.
Most important, Relenza does not make flu vaccinations obsolete. "Relenza is not a substitute for vaccination," Karron warns. "Ideally the goal of vaccinations is to prevent infection, rather than just alleviate the symptoms."
"The influenza vaccine is clearly the most cost-effective way of preventing infection," Hayden adds.
Facing the needle for a few seconds isn't all that bad, considering the alternative, Mary Scarless said recently as she waited for a flu shot at the Waxter Senior Center on Cathedral Street.
Last year, Scarless, who is 74, contracted the flu even though she had been vaccinated. She missed her first day of work in eight years. Her friends wouldn't visit for fear of contracting the virus themselves, they just left grapefruit juice outside her door, rang the bell and scurried away.
"I don't want to get it again," she says. "Having the flu is like being in exile."