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Influenza Information for Clinicians–Season 2010-2011
Influenza Facts
Influenza viruses are spread from person to person primarily through large-particle respiratory droplet
transmission. Transmission via large-particle droplets requires close contact between source and
recipient persons, because droplets do not remain suspended in the air and generally travel only a short
distance (less than or equal to 1 meter) through the air. Contact with respiratory-droplet contaminated
surfaces is another possible source of transmission. The typical incubation period for influenza is 1—4
days (average: 2 days). Adults shed influenza virus from the day before symptoms begin through 5—10
days after illness onset. Young children also might shed virus several days before illness onset, and
children can be infectious for 10 or more days after onset of symptoms.
Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and respiratory
signs and symptoms (e.g., fever, myalgia, headache, malaise, nonproductive cough, sore throat, and
rhinitis). Among children, otitis media, nausea, and vomiting also are commonly reported with influenza
illness. Influenza virus infections can cause primary influenza viral pneumonia; exacerbate underlying
medical conditions (e.g., pulmonary or cardiac disease); lead to secondary bacterial pneumonia,
sinusitis, or otitis media; or contribute to coinfections with other viral or bacterial pathogens. Young
children with influenza virus infection might have initial symptoms mimicking bacterial sepsis with high
fevers, and febrile seizures. Influenza virus infection also has been uncommonly associated with
encephalopathy, transverse myelitis, myositis, and myocarditis, pericarditis, and Reye syndrome.
Influenza A and B are the two types of influenza viruses that cause epidemic human disease. Influenza A
subtypes and B viruses are separated further into groups on the basis of antigenic similarities. New
influenza virus variants result from frequent antigenic change caused by mutations and recombination
events that occur during viral replication. Antibody against one influenza virus type or subtype confers
limited or no protection against another type or subtype of influenza virus. Frequent emergence of
variants is the basis for seasonal epidemics and is the reason for annually reassessing the need to
change one or more of the recommended strains for influenza vaccines.
Influenza Vaccine Composition
Live, Attenuated Influenza Vaccine (LAIV) or Inactivated Influenza Vaccine (TIV) is used
for seasonal influenza vaccination. Both contain strains of influenza viruses that match the
annual strains: one influenza A (H3N2) virus, one influenza A (H1N1) virus, and one influenza B virus.
Each year, one or more virus strains in the vaccine might be changed on the basis of global surveillance
for influenza viruses and the emergence and spread of new strains.
The major difference between TIV and LAIV is that TIV contains inactivated viruses and thus
cannot cause influenza. LAIV contains live attenuated influenza viruses that have the potential to cause
mild signs or symptoms. LAIV is administered intranasal by sprayer, whereas TIV is administered
intramuscularly by injection. LAIV is licensed for use among nonpregnant persons aged 2–49 years;
safety has not been established in persons with underlying medical conditions that confer a higher risk
for influenza complications. TIV is licensed for use among persons aged 6 months and older, including
those who are healthy and those with chronic medical conditions.
Influenza Information for Clinicians–Season 2010-2011
2010–2011 seasonal influenza vaccine
This year’s vaccine is designed for protection against
 an A/California/7/2009 (H1N1)–like virus;
 an A/Perth/16/2009 (H3N2)–like virus;
 and a B/Brisbane/60/2008–like virus.
The location in the name is given to indicate the first identifies location of this particular strain.
The H1N1 virus recommended for inclusion in the 2010-2011 seasonal influenza vaccine is a pandemic
2009 H1N1 virus and is the same vaccine virus as was used in the 2009 H1N1 vaccine. Viruses for
currently licensed TIV and LAIV preparations are grown in chicken eggs.
Dosage and Administration
The composition of TIV varies according to manufacturer, and package inserts should be consulted. TIV
formulations in multi-dose vials contain the vaccine preservative thimerosal but preservative-free,
single-dose preparations also are available. TIV should be stored at 35°F--46°F (2°C--8°C) and should not
be frozen. TIV that has been frozen should be discarded. Dosage recommendations and schedules vary
according to age group. Vaccine prepared for a previous influenza season should not be administered to
provide protection for any subsequent season.
Each dose of LAIV contains the same three vaccine antigens used in TIV. However, the antigens are
constituted as live, attenuated, cold-adapted, temperature-sensitive vaccine viruses. Providers should
refer to the package insert, which contains additional information about the formulation of this vaccine
and other vaccine components. LAIV does not contain thimerosal. LAIV is made from viruses that are
able to replicate efficiently only at temperatures present in the nasal mucosa. LAIV recipients might
experience nasal congestion or mild fever, which is probably a result of effects of intranasal vaccine
administration or local viral replication.
Diagnostic Testing for Influenza
Rapid diagnostic tests for influenza can help in the diagnosis and management of patients who present
with signs and symptoms compatible with influenza. They also are useful for helping to determine
whether outbreaks of respiratory disease, such as in nursing homes and other settings, might be due to
influenza. In general, rapid diagnostic testing for influenza should be done when the results will affect
clinical decision making.
The reliability of rapid diagnostic tests depends largely on the conditions under which they are used.
Understanding some basic considerations can minimize being misled by false-positive or false-negative
results.
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Sensitivities of rapid diagnostic tests are approximately 50-70% when compared with viral
culture or reverse transcription polymerase chain reaction (RT-PCR), and specificities of rapid
diagnostic tests for influenza are approximately 90-95%.
False-positive (and true-negative) results are more likely to occur when disease prevalence in
the community is low, which is generally at the beginning and end of the influenza seasons.
False-negative (and true-positive) results are more likely to occur when disease prevalence is
high in the community, which is typically at the height of the influenza season.
Influenza Information for Clinicians–Season 2010-2011
Influenza vaccines available for 2010-2011
Vaccine Trade Name
Manufacturer
Presentation
Mercury Content
TIV
Fluzone
Sanofi Pasteur
0.25 mL prefilled syringe
0.5 mL prefilled syringe
5.0 mL multi-dose vial
0
0
2 5mcg Hg/0.5 mL
TIV
Fluvirin
Novartis
5.0 mL multi-dose vial
0.5 mL prefilled syringe
25 mcg Hg/0.5 mL
Less than 1.0 mcg
TIV
Agriflu
Novartis
0.5 mL prefilled syringe
0
TIV
Fluarix
GlaxoSmithKline
0.5 mL prefilled syringe
0
TIV
FluLaval
ID Biomedical Corp.
5.0 mL multi-dose vial
25 mcg Hg
TIV
Afluria
CSL Biotherapies
0.5 mL prefilled syringe
0
TIV
Fluzone
Sanofi Pasteur
0.5 mL prefilled syringe
0
LAIV
FluMist
Medimmune
0.2 mL sprayer, divided doses
0
Influenza Information for Clinicians–Season 2010-2011