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Why The CDC And FDA Are Telling You Two Different Things About Flu Drugs

You’re coughing, you’re congested, and your head hurts. You’re achy and feverish, and your throat is killing you. A quick Google search reveals that you probably have the flu. What’s your next move? You could call in sick and quarantine yourself at home while you nurse your symptoms with cough drops, an over-the-counter remedy, chicken soup and a Netflix binge. Or you could go to your doctor and get a prescription for an antiviral influenza drug, something like Tamiflu.

The Centers for Disease Control and Prevention recommends the latter approach.

The CDC released figures Thursday showing that this season’s influenza vaccine is only about 23 percent effective, and the federal agency recently sent a letter to doctors, urging them to write more prescriptions for influenza drugs.

“Antiviral flu medicines are underutilized. If you get them early, they could keep you out of the hospital and might even save your life,” CDC Director Tom Frieden told reporters Jan. 9. Flu season lasts, on average, about 13 weeks. We’re about midway through a particularly bad one.

According to Frieden, three flu medications (Tamiflu, Relenza and Rapivab) can prevent “serious complications” and help people avoid hospitalization. But the Food and Drug Administration explicitly prohibits drug companies from making the claims that he and the CDC are making. Two different agencies, two different recommendations.

Listen to Christie Aschwanden discuss this story, and what you should do if you’re feeling flu-like symptoms, here:

FDA spokeswoman Stephanie Yao told FiveThirtyEight in a statement: “Please note that neither product” — Rapivab nor Tamiflu — “is allowed to claim that they reduce complications or mortality due to flu. The data we’ve reviewed do not support this claim.” What the drugs have demonstrated, she said, is, “an ability to reduce the severity or duration of flu symptoms.”

The discrepancy between the CDC’s assertion that the flu drugs can prevent complications, hospitalizations and perhaps deaths, and the FDA’s insistence that the drugs have only been shown to cut the amount of time that symptoms persist comes down to how they weigh the evidence. The FDA requires randomized clinical trials, the gold standard of evidence in medicine, while the CDC also relies on non-randomized reports. “Observational studies from many countries have consistently found that early oseltamivir [Tamiflu] treatment of influenza patients reduces the duration of hospitalization and risk of severe outcomes such as intensive care unit admission or death,” CDC spokeswoman H. Amy Rowland told FiveThirtyEight in a statement.

But physician Tom Jefferson of the Cochrane Collaboration, an international organization that assesses medical evidence, calls the studies that the CDC is using to tout the drugs poorly designed and unreliable, pointing out that they’re funded by the drugs’ maker and led by researchers tied to the manufacturers. More rigorously designed trials do not back them up. For example, a study published last month that randomly assigned 400 hospitalized patients to receive either the newly approved peramivir (Rapivab) or a placebo was halted early for “futility” when it became clear that patients receiving the drug weren’t benefitting.

All three antiviral medications are designed to inhibit neuraminidase, an enzyme that influenza viruses need to release viral particles from infected cells. If the drugs can prevent the replication of these viruses, that’s a big deal, because they could stem the spread of the flu, making them vital tools for controlling epidemics. (This is why the U.S. has reportedly spent about $1.5 billion stockpiling Tamiflu.) But Jefferson said clinical trials hint that the drugs may not work as advertised. In studies where people with influenza-like illnesses were assigned to either a neuraminidase inhibitor or a placebo, the drugs worked for people with influenza and for those who tested negative for the flu. (Because it takes a few days for test results and the drugs work best when given soon, patients were started on the drugs before the results were in.) Although other viruses can cause flulike symptoms, neurominadase isn’t found in other respiratory viruses, Jefferson said. So, he said, if the drug works for both groups of patients, it must be acting via a different mechanism. And if the drugs are simply reducing fevers and making people feel better via some other mechanism, then it’s possible they’re nothing more than expensive alternatives to acetaminophen and ibuprofen, which alleviate aches and reduce fevers. (Tamiflu retails for about$130, Relenza goes for about $67, and Rapivab costs about$1,000.) Right now, there’s not enough evidence to draw firm conclusions on the drug’s actual mechanism of action, and Jefferson, his colleagues at Cochrane and editors at the British medical journal BMJ are embroiled in a years-long effort to obtain complete clinical trials data from the maker of Tamiflu.

Last April, Jefferson’s group published its latest meta-analysis of all the evidence it could get on Tamiflu, including thousands of pages of regulatory documents describing the various clinical trials. The researchers concluded that the drug can reduce the duration of flu symptoms by a little less than a day in adults. (The results are similar for the other antiviral drugs.) A typical case of influenza lasts about one to two weeks, and when you’re in the throes of it, something that can make your misery vanish a day sooner might seem very appealing.

Here’s the rub: For the drugs to work, you need to take them in the first 48 hours from the onset of symptoms. Think back to the last time you were sick — how long did you feel cruddy before you sought a doctor’s help? It’s this lag between the first sniffle and the pursuit of medicine that the CDC hopes to bridge with its public messaging push so that more people get to the doctor in time for the medications to help.

But whether they’re worth the hassle for otherwise healthy people remains a personal choice, said Brian Alper, a physician and founder of DynaMed, a company that monitors and assesses the latest medical evidence to inform doctors. The organization has analyzed the evidence on these drugs, reaching conclusions similar to the Cochrane review. To decide whether the drugs are right for you means taking into account the hassle of landing an appointment, going to the pharmacy, potential side effects (such as vomiting, dizziness and delirium), and, of course, paying for these things. If your doctor’s office has no wait, and you’re insured with a plan that covers most of the cost, seeking the drugs might be an easy choice, Alper said. But if you can’t get seen right away, the doctor’s office is far, or you’re likely to be stuck with some of the bill, you may end up spending a day of hassle and expense (while you’re feeling lousy) to save yourself a day of symptoms.

Of course, much of the concern over influenza isn’t centered on otherwise healthy individuals, but on people with underlying health problems. And the CDC contends that the flu drugs do more than just reduce the duration of symptoms — they could mean the difference between life and death. Whether that’s true matters, because sending sick, contagious people out to the doctor and pharmacy could further spread an influenza outbreak. People with underlying health problems, such as severe asthma or immune deficiencies, should certainly seek a medical care at the first sign of flu symptoms. But if you’re generally healthy, it may be that the best thing you can do for yourself, and your community, is stay home and practice some self-care.

Christie Aschwanden is FiveThirtyEight’s lead writer for science.

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