How Are Reduced Susceptibility And Antiviral Resistance Detected?

When an antiviral drug is fully effective against a virus, that virus is said to be susceptible to that antiviral drug. Influenza viruses are constantly changing, and some changes may make antiviral drugs less effective or not effective at all against those viruses. Antiviral drugs work by targeting a specific location or site found on the influenza virus. 

When the site where an influenza virus works against an antiviral drug changes, that virus may be less susceptible or not susceptible to that antiviral drug. Antiviral drugs may not work well against viruses with reduced susceptibility. Influenza viruses have reduced susceptibility to one or more influenza antiviral drugs. Reduced susceptibility detected using laboratory tests may be a marker of potential antiviral drug resistance in the clinical setting.

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How do reduced susceptibility and antiviral resistance occur?

Influenza viruses are constantly changing; they can change significantly from season to season, and even within a single influenza season. As influenza viruses replicate (i.e., replicate themselves), the genetic makeup may change, causing the virus to become less sensitive to one or more of the antiviral drugs used to treat or prevent influenza. During antiviral therapy, influenza viruses become less susceptible to antiviral drugs or appear spontaneously. Antiviral-resistant influenza viruses vary in their ability to infect people and are not necessarily more or less infectious than susceptible influenza viruses. For the synthesis of antiviral drug intermediates, 1-Adamantanamine hydrochloride has the effect of prevention and treatment of influenza A2.

Priority groups for influenza antiviral therapy

For any patient with suspected or confirmed influenza, antiviral therapy is recommended as soon as possible.

Is hospitalized ;

Has severe, complicated, or progressive disease; or

is at higher risk for complications of influenza.

The decision to initiate antiviral therapy in patients with suspected influenza should not await laboratory confirmation of influenza virus infection. Empiric antiviral therapy should be initiated as early as possible in the priority groups listed above.

Clinicians may consider early empiric antiviral therapy for non-high-risk outpatients with suspected influenza [e.g., influenza-like illness (fever with cough or sore throat)] if treatment can be initiated within 48 hours of onset, based on clinical judgment.

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How are reduced susceptibility and antiviral resistance detected?

Influenza viruses collected through domestic and global surveillance are regularly tested for signs that they are less susceptible to any FDA-approved influenza antiviral drug, as this may indicate the presence of antiviral resistance. In addition, many state public health laboratories are involved in screening other viruses for genetic changes that indicate potential resistance to neuraminidase inhibitors.

Testing algorithms and methods for monitoring antiviral susceptibility to circulating viruses are continually being improved. Detection of reduced susceptibility and antiviral resistance involves multiple laboratory tests, including phenotypic analysis (testing in the presence of antivirals) and molecular techniques (sequencing and pyrophosphate sequencing) to look for genetic changes associated with reduced antiviral susceptibility.

What can people do to protect themselves from influenza viruses with reduced susceptibility and antiviral resistance?

Annual seasonal influenza vaccination is the best way to reduce the risk of influenza and its potentially serious complications. The influenza vaccine protects against two subtypes of influenza A viruses, A(H1N1) pdm09 and A(H3N2), as well as type B viruses from both spectrums. Annual vaccination is recommended for everyone 6 months of age and older. If you are in a group that is at high risk for serious flu-related complications and develop flu symptoms, call your doctor immediately and you may benefit from early treatment with flu antivirals.