Atlanta—Influenza activity has increased significantly in the United States over the last few weeks, according to the CDC, which issued a health alert about the flu.

The concern is that influenza A(H3N2) viruses have been most common so far this season, and, in past years, more hospitalizations and deaths in patients aged 65 years and older or young children have occurred when that virus is predominant.

At the same time, public health officials caution that influenza-vaccine effectiveness (VE) in general has been lower against A(H3N2) viruses than against influenza A(H1N1)pdm09 or influenza B viruses. Last season, for example, the vaccine was only 32% effective against circulating influenza A(H3N2) viruses in the U.S., and the CDC expects similar performance this season.

While still heavily promoting immunization, the health agency is also emphasizing the importance of antiviral medications. “The neuraminidase inhibitor (NAI) antiviral medications are most effective in treating influenza and reducing complications when treatment is started early,” the health alert states. “Evidence from previous influenza seasons suggests that NAI antivirals are underutilized in outpatients and hospitalized patients with influenza who are recommended for treatment.”

The CDC said it issued the alert to remind clinicians to consider influenza as a diagnosis for ill patients because the viral infection is increasing so much nationwide and also to advise that hospitalized patients and all high-risk patients—whether hospitalized or outpatient—be treated as soon as possible for suspected influenza with a neuraminidase inhibitor antiviral. 

“While antiviral drugs work best when treatment is started within two days of illness onset, clinical benefit has been observed even when treatment is initiated later,” the alert explains.

Among high-risk patients are any who are at higher risk for influenza complications but are not hospitalized, including children younger than age 2 years (although all children younger than age 5 years are considered at higher risk for complications from influenza, the highest risk is for those younger than 2 years); adults 65 years and older, and those with a variety of chronic illnesses and conditions.

Other groups, such as pregnant/postpartum women, nursing home residents, the extremely obese, and American Indians/Alaska Natives also are considered high risk.

In those patients, the CDC strongly urges that antiviral treatment be started as soon as possible after illness onset and should not be delayed even for a few hours to wait for the results of testing. Instead, public health officials recommend that empiric antiviral treatment should generally be initiated as soon as possible when there is known influenza activity in the community. In fact, it even advises that an antiviral prescription can be provided without testing and before an office visit if high-risk patients report flu-like symptoms to their physician offices.

The health alert also cautions that a history of current-season influenza vaccination does not exclude a diagnosis of influenza in an ill child or adult. 

Three prescription neuraminidase inhibitor antiviral medications are approved by the FDA and are recommended for use in the U.S. during the 2017–2018 influenza season: oseltamivir, zanamivir, and peramivir.
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