The overall estimated effectiveness of the seasonal influenza vaccine was found to be 45%, according to data from the US Influenza Vaccine Effectiveness Network.
The interim data, published in the latest Morbidity and Mortality Weekly Report, showed that among 4112 children and adults enrolled in the US Flu VE Network during October 23, 2019 and January 25, 2020, overall vaccine effectiveness against any influenza virus associated with medically attended acute respiratory infection was 45% (95% CI, 36-53); vaccine effectiveness against influenza B/Victoria viruses and influenza A (H1N1)pdm09 was observed to be 50% and 37%, respectively. Among children and adolescents 6 months to 17 years of age, the study showed substantial protection (vaccine effectiveness: 55%; 95% CI, 42-65).
According to the report, while both viruses have been detected this season, the influenza B/Victoria strain has been the predominant circulating virus, with increases in influenza A (H1N1)pdm09 beginning in late December 2019. The CDC continues to recommend influenza vaccination for patients ≥6 months without contraindications to protect against illness and potentially serious complications.
In addition, antiviral medications are recommended for patients with suspected or confirmed influenza who are hospitalized, have severe or progressive illness, or are at high risk for complications, including children <2 years old and adults ≥65 years, regardless of vaccination status or results of point-of-care influenza diagnostic testing. For outpatients with acute uncomplicated influenza, oseltamivir, zanamivir, peramivir, or baloxavir may be used. For patients with severe or complicated illness (ie, pneumonia or exacerbations of an underlying chronic medical condition) who are not hospitalized, treatment with oral or enterically-administered oseltamivir is recommended as soon as possible.
The authors of the MMWR report do list several limitations to their findings including sample size, self-reporting of vaccination status, observational study design, and vaccine effectiveness estimates being limited to the prevention of outpatient medical visits rather than more severe illness outcomes (ie, hospitalization, death).
“These interim [vaccine effectiveness] estimates indicating a 45% reduction in influenza illness associated with a medical visit so far this season are particularly important in the context of the substantial prevalence of influenza in the United States: during the previous decade, influenza caused an estimated 4.3-21 million doctor visits, 140,000-810,000 hospitalizations, and 12,000-61,000 deaths each year,” the authors concluded.
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