Public health officials urge pharmacists and other healthcare professionals to keep promoting immunization.
In an interim report in the Morbidity & Mortality Weekly Report, CDC researchers emphasize that, because flu activity is likely to continue for several more weeks in the United States, vaccination efforts should continue as well.
Anyone 6 months or older who has not yet received the 2016-2017 influenza vaccine should be vaccinated as soon as possible, according to the CDC, which also notes that, as of early February, about 145 million doses of influenza vaccine had been distributed in the United States for the 2016-2017 season.
Thus far in the flu season, overall vaccine effectiveness (VE) against influenza A and influenza B virus infection was 48%, with most influenza infections caused by A (H3N2) viruses, the CDC reports. VE was estimated to be 43% against illness caused by influenza A (H3N2) virus and 73% against influenza B virus. The report uses data from 3,144 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network from November 28, 2016 to February 4, 2017.
Because, during 2014-2015, influenza A (H3N2) 3C.2a viruses were antigenically different from the recommended A (H3N2) vaccine component, low vaccine effectiveness of 1% resulted, contributing to high rates of influenza-associated hospitalizations that season, especially among older adults.
This flu season, however, rates of influenza-associated hospitalizations observed so far have been substantially lower. Virologic surveillance indicates that the majority of influenza A (H3N2) viruses collected by U.S. laboratories during the 2016-2017 season remain antigenically similar to the A/Hong Kong/4801/2014–like cell-propagated reference virus belonging to genetic group 3C.2a, which is the recommended influenza A (H3N2) component of the 2016-2017 Northern Hemisphere vaccine.
Public health officials also caution that influenza activity remained elevated nationally and was widespread across most of the U.S. as of late February.
“Clinicians should maintain a high index of suspicion for influenza infection among persons with acute respiratory illness while influenza activity is ongoing, especially among older adults,” the CDC advises. “Early antiviral treatment can reduce severity and complications of influenza-associated illness. Early antiviral treatment is recommended for persons with suspected influenza with severe or progressive illness (e.g., hospitalized persons) and persons at high risk for complications from influenza, such as children aged <2 years, adults aged ≥65 years, and persons with underlying health conditions, even if illness is less severe. Antiviral medications should be used as recommended for treatment in patients with suspected influenza, regardless of vaccination status.”
It further emphasizes that the decision to initiate antiviral treatment should not be delayed while waiting for laboratory confirmation of influenza and should not be dependent on insensitive assays, such as rapid influenza-diagnostic tests.
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