Key Points
ÎÎInfluenza illness is caused by infection with 1 of 3 types of circulating
RNA viruses: influenza A, B, or C virus. Influenza C virus infection
causes respiratory illness that is generally milder than influenza A and
B virus infections and for which diagnosis, treatment, and prevention
are generally not pursued.
ÎÎDuring influenza season, influenza viruses circulate ubiquitously in
the population. Each year, between 5% and 20% of the population
are infected with influenza viruses, and an estimated annual average
of 36,000 deaths and over 200,000 hospitalizations attributable to
influenza virus infection occur in the United States.
ÎÎThe elderly, the very young, and persons with underlying medical
conditions such as those with cardiopulmonary disease, persons with
diabetes, immunocompromised persons, morbidly obese persons,
and pregnant women are at increased risk for severe disease or death
secondary to influenza virus infection.
ÎAppropriate use of diagnostic testing, along with timely administration
Î
of antiviral medications, may improve clinical outcomes of influenza
virus infection, may reduce other unnecessary diagnostic testing, may
decrease duration of required medical care, and may reduce both
appropriate use (for presumed bacterial complications) and inappropriate
use (to prevent bacterial complications) of antibacterial agents.
Shedding Time
ÎÎImmunocompetent persons: may be up to 5 days from onset
ÎÎInfants and young children: commonly 1 week or longer
ÎÎImmunocompromised persons: may be several weeks
Vaccination
In general, inactivated influenza vaccine is contraindicated for, and should not be
administered to, persons known to have anaphylactic hypersensitivity to eggs or to
any vaccine components. Recombinant influenza vaccine (Flublok®) can be given
safely to such persons. Guillain-Barré syndrome within 6 weeks following a previous
dose of influenza vaccine is considered a precaution for use of influenza vaccines.
ÎÎInfluenza vaccination is the primary tool to prevent influenza,
and antiviral chemoprophylaxis is not a substitute for influenza
vaccination.
• Quadrivalent vacccines provide protection against both lineages of influenza B
virus whereas trivalent vaccines contain only one B lineage.
ÎÎInfluenza vaccine should be administered as soon as vaccine is
available, and vaccination efforts should continue until influenza is no
longer in the community (B-II).
ÎÎVaccination is particularly important for all family members when
1 person or more is at high risk of complications (A-I).