While it’s been one of the most severe seasons in recent history, the flu is finally waning. But it's not quite finished with us, yet. In fact, influenza is still widespread in 34 states, according to the Centers for Disease Control and Prevention’s latest update. Just in case it comes your way in the next month or so (May is the outer boundary of traditional seasons), we asked Angela Campbell, M.D., a medical officer with CDC's Influenza Division, for a detailed look at antivirals — what she calls the second most important way, after your flu shot, to protect yourself.
Can you explain for us how the three types of antivirals on the market (commonly known by their brand names Tamiflu, Relenza and Rapivab) work?
The three antiviral drugs that are approved and recommended for use this season are all neuraminidase inhibitors, and this class of drugs works by blocking the release of virus particles from infected cells. That keeps the virus from going on and infecting other cells.
Basically, the flu virus infects a cell in the respiratory tract and then it makes new copies of itself inside the cell. These copies need to be released to go out and infect other cells. The molecule that does the release is called the neuraminidase, and these neuraminidase inhibitors block that release action.
How soon after taking a prescribed antiviral could someone expect to feel better?
One trial showed that an antiviral given to adult outpatients within the first two days of illness shortened the time that it would otherwise take for all symptoms to resolve, or go away, by one day. But there were data to show that even within that first 48 hours, the duration of illness was shorter the earlier the treatment was initiated. So it's shorter if treatment is given within the first six hours than if it’s given within 12 hours, all the way up to 48 hours. And if you think about how these drugs work — blocking virus release from the cells — it makes sense that the earlier in the infection you give one, the more it will keep the virus from multiplying and spreading.
Is there any research on whether you get any benefit if you take one after the first couple of days?
There are some studies that show that treatment started even after 48 hours from symptom onset can be beneficial. A Lancet Infectious Diseases study from 2013 suggested a benefit when oseltamivir [available under the brand name Tamiflu or as a generic version] was started even 72 hours after illness onset in children with fever. There have also been other observational studies in hospitalized patients that have shown that treatment can provide a benefit when started 3 to 5 days after the onset of symptoms. So for that reason, we recommend that a hospitalized patient with suspected or confirmed influenza be started as soon as possible on antiviral treatment even if it’s outside of that 48-hour window.
How else can something like Tamiflu help?
We have data that suggest that antivirals also reduce the risk of complications, such as lower respiratory tract infections like pneumonia. And there’s some data to suggest they reduce the risk of being admitted to the hospital. And then in hospitalized patients, we have observational data that show that influenza antivirals can both reduce mortality and shorten the length of stay.
How big of a reduction in mortality are you talking?
There was a study in 2014, which included data on more than 29,000 patients, which showed that treatment with a neuraminidase inhibitor was associated with a 25 percent reduction in the likelihood of death compared to receiving no treatment. If the antiviral was given within 48 hours of a person developing illness, it cut the risk of death in half.