HERIBERTO SEDENO, M.D. LECTURE ON INFLUENZA

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HERIBERTO SEDENO, M.D. LECTURE ON INFLUENZA
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INFLUENZA Influenza is a potentially severe acute
respiratory illness caused by various strains of
the influenza virus. The different strains all
produce characteristic symptoms, and because
major outbreaks are associated with increased
mortality, occurrences can be identified in
history. Outbreaks consistent with influenza can
be traced back at least to the court of Elizabeth
I. Some have speculated that the Plague of Athens
described by Thucydides was influenza complicated
by bacterial superinfection. The influenza
syndrome, commonly known as the flu, with its
fever, cough, rapid onset and body aches, is not
only typical enough to be recognized in the past,
but it also allows physicians to recognize it,
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especially when it is known that the virus is
circulating. Unfortunately, death is the other
consistent phenomena associated with
influenza. Mortality statistics are the principal
way the intensity of an influenza outbreak is
quantified, and are so characteristic that viral
identification of etiology is not
required. PREVENTION AND CONTROL OF INFLUENZA A
vaccine for the prevention of influenza was
developed during World War II in order to
maintain military readiness. This was done in
recognition of the high morbidity that could
result among troops exposed to the virus. A
similar inactivated vaccine is still in use,
improved in both potency and lack of side
effects.
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It is known to be 70 to 90 percent efficacious in
healthy young adults as long as the vaccine
viruses resemble those circulating. This
necessitates updating the viruses in the vaccine
each year. For this and other reasons, the
vaccine must be given annually. Since vaccination
programs must be sustained, the goal in most
countries has been to reduce influenza mortality
by vaccinating older individuals and those with
chronic underlying diseases. An exception to this
has been Japan, where, for a time, school-age
children were vaccinated in an effort to control
influenza morbidity. It has been repeatedly
demonstrated that the inactivated vaccine is
effective in preventing hospitalization and death
in older individuals and,
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as such, is also cost effective. The inactivated
vaccine is cost effective in healthy adults only
when the attack rates are above 12 percent. A
live attenuated influenza vaccine has been used
in the former Soviet Union for many years, and
another is in development in the United States.
Because of its deliveryintranasally rather than
by injectionit may prove to be particularly
useful in children and younger adults. Antiviral
drugs have been available both for treatment and
prophylaxis. Two of these are active only against
type A viruses. A new group of drugs, acting as
neuraminidase inhibitors, is active against both
type A and B viruses.
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These drugs have been shown to have a prevention
efficacy similar to vaccines. They start
protecting more quickly than the vaccine, but
have to be taken daily to continue protection.
Therefore, vaccination will continue to be the
usual means of prophylaxis.The neuraminidase
inhibitors also significantly shorten the
duration of illness, reducing severity and
preventing complications. Influenza can be
debilitating, even in the absence of
complications, so that the drugs will be used for
treatment during defined influenza outbreaks.
They are likely also to be useful
prophylactically, especially for outbreak control
in nursing homes.
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