administered ≥4 weeks after the first dose. The immune response
peaks 2 weeks after the second dose.
ÎÎInfluenza vaccination may have lower effectiveness in persons who are
significantly immunocompromised.
Diagnosis and Assessment
Table 1. Persons Who Should Be Tested for Influenza
During influenza season, testing should occur in the following persons if the result will
influence clinical management:
• Outpatient immunocompetent persons of any age at high-risk for complications of
influenza presenting with acute febrile respiratory symptoms, within 5 days of illness
onset, when virus is usually being shed
• Outpatient immunocompromised persons of any age presenting with
febrile respiratory symptoms, irrespective of time from illness onset, since
immunocompromised persons can shed influenza viruses for weeks to months
• Hospitalized persons of any age (immunocompetent or immunocompromised) with
fever and respiratory symptoms, including those with a diagnosis of communityacquired pneumonia, irrespective of time from illness onset
• Elderly persons and infants with suspected sepsis irrespective of time from illness onset
• Children with fever and respiratory symptoms presenting for medical evaluation
irrespective of time from illness onset
• Persons of any age that develop fever and respiratory symptoms after hospital
admission, irrespective of time from illness onset
• Immunocompetent persons with acute febrile respiratory symptoms but not at high
risk of complications secondary to influenza infection may be tested for purposes of
obtaining local surveillance data
At any time of the year, testing should occur in the following persons:
• Healthcare personnel, residents, or visitors in an institution experiencing an influenza
outbreak who present with febrile respiratory symptoms within 5 days of illness onset
• Persons who are epidemiologically linked to an influenza outbreak (eg, household
and close contacts of persons with suspected influenza; returned travelers from
countries where influenza viruses may be circulating; participants in international
mass gatherings; cruise ship passengers), within 5 days of illness onset
Specimen Collection (all A-II)
ÎÎCollect from immunocompetent persons within 5 days of onset
ÎÎPreferred specimens:
• Infants and young children: nasal aspirates and swabs
• Older children and adults: nasopharyngeal aspirates and swabs
• Mechanically ventilated patients: upper and lower respiratory tract samples
ÎÎRefrigerate immediately
ÎÎConsult test instructions for preferred swab type for each test
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