Bracing for a Severe Flu Season

According to the US Centers for Disease Control and Prevention (CDC), 51,895 respiratory specimens tested positive for influenza across the United States and Puerto Rico between September 28, 2014, and January 3, 2015. Of those viruses, 94.6% were influenza A (predominantly H3N2) and 5.4% were influenza B.

Although this season’s influenza vaccine only reduces a recipient’s risk of flu-related medical visits by 23%, the CDC still advises those who have not yet received the influenza vaccine to get immunized, given that it may protect against some current flu viruses, as well as those that may circulate later.

Historically, flu seasons during which H3N2 was the predominant strain had more severe flu infections with more hospitalizations and a higher mortality rate, especially among patients aged younger than 2 years or 65 years and older. In order to avoid poor flu outcomes, a 3-pronged approach is necessary to fight the flu: vaccination, prompt treatment, and preventative health measures, such as hand washing and staying at home when you are sick.

Early treatment with antiviral drugs can shorten the duration of fever and illness symptoms, reduce risks for complications, and prevent mortality. For optimatl outcomes, antiviral drugs should be started within 48 hours of symptom onset. However, antiviral treatment may still provide benefits when started after 48 hours of symptom onset in patients with severe, complicated, or progressive illness.

Treatment with older antiviral drugs for influenza, such as amantadine and rimantadine, has become obsolete due to resistance. That leaves 3 antiviral drugs to treat influenza: oral oseltamivir (Tamiflu), orally inhaled zanamivir (Relenza), and intravenous peramivir (Rapivab).

Tamiflu is indicated for the treatment of influenza in patients aged 2 weeks and older and for prophylaxis in patients aged 1 year and older. Although they are not part of the FDA-approved indications, oseltamivir therapy is also recommended for treatment in infants aged <2 weeks old and for prophylaxis in infants aged 3 months to 1 year by the CDC and the American Academy of Pediatrics Committee on Infectious Disease. Oseltamivir is also the preferred treatment in pregnant woman, with no dosage changes.

Relenza is approved for treatment in patients aged 7 years and older and as prophylaxis in patients aged 5 years and older. In otherwise healthy individuals, the benefits of zanamivir appear to be small, and the risk for virus strain resistance, side effects, and cost outweigh those small benefits.

Rapivab was approved by the FDA on December 19, 2014, as a single dose, intravenous antiviral intended for patients aged 18 years and older who have acute, uncomplicated influenza and have shown symptoms for no more than 2 days.

The CDC does not recommend the use of antiviral medications as prophylaxis on a routine basis. Indiscriminate use may promote resistance and reduce antiviral medication availability for patients at high risk or those who are severely ill.