Two antiviral drugs, oseltamivir and
zanamivir, are highly effective when given as a preventive measure to
reduce the spread of the influenza virus, according to an analysis of
household-based studies by researchers at Fred Hutchinson Cancer Research
Center, University of Michigan and University of Virginia, published in the
current print edition of the American Journal of Epidemiology. The analysis
also suggests that treatment with oseltamivir may reduce the infectiousness
of influenza patients, although further studies are needed to provide a
definitive conclusion.
"Preventing the spread of influenza within families is an essential
part of influenza management, regardless of the strain. This study shows
that there is a clear benefit to be gained by giving antivirals to people
who have been exposed to the virus to prevent the onset of symptomatic
illness," said lead author M. Elizabeth (Betz) Halloran, M.D., D.Sc., a
Hutchinson Center-based biostatistician.
"While the efficacy of antivirals to protect against influenza is
critical, the effect of these drugs on infectiousness also has important
public-health consequences. Further studies to determine antiviral efficacy
for reducing infectiousness would therefore be of great value," said
Halloran, a member of the Hutchinson Center's Public Health Sciences
Division and a professor of biostatistics at the University of Washington
School of Public Health and Community Medicine.
The report evaluated four household-based, randomized,
placebo-controlled clinical trials, conducted from 2000 to 2004, which were
designed to estimate the effect of post-exposure antiviral treatment on
preventing influenza within households. Two of the trials were conducted
with zanamivir and two with oseltamivir, permitting comparisons to be made
between the two. The trials covered a total of 1,475 households. The
majority of first household cases (53 percent to 70 percent) had influenza
A (H3N2 or H1N1).
The authors reviewed the effects of each antiviral on infectiousness
and pathogenicity -- the ability of the influenza virus to cause overt
disease. Pathogenicity in controls ranged from 44 percent to 66 percent.
Efficacy in reducing pathogenicity for zanamivir was 52 percent and 56
percent in the two zanamivir studies; for oseltamivir, it was 56 percent
and 79 percent. The researchers found that both drugs were highly
preventive against influenza illness, with oseltamivir at 81 percent
efficacy and zanamivir at 75 percent. Thus, the preventive use of either
product reduced by 75 percent to 81 percent the chance that an exposed
person would become ill with influenza.
The researchers' analysis found a significant reduction in
infectiousness, as defined by reductions in influenza illnesses in
household contacts, when oseltamivir was used for treatment of ill persons,
but not when zanamivir was administered. Although these results are of
interest, the authors stress that the numbers were small and combined
estimates from two studies for each drug were used in both instances.
Furthermore, oseltamivir treatment of ill persons did not appear to reduce
the frequency of influenza infection in their contacts.
In exploring the reasons for oseltamivir's greater effects on
infectiousness, the authors speculated that the different modes of
administration -- oral for oseltamivir and inhaled for zanamivir -- and
resultant upper-respiratory viral levels could be the key, with zanamivir
not reaching or affecting influenza virus in the nose. While both
antivirals reduced cough, in earlier studies inhaled zanamivir did not
significantly reduce nasal symptoms. In the paper the authors discussed the
possibility that infectious droplets inhaled and exhaled from the nose may
be important in viral transmission, thus orally administered oseltamivir
might have an advantage in limiting spread.
In addressing the limitations to their research, the authors call for
further studies into antiviral efficacy. "Trials in non-household settings
where influenza readily spreads -- such as schools, homes for the elderly
and workplaces -- would be beneficial not only for planning management of
seasonal influenza but also would be invaluable in pandemic planning.
Additionally, simple solutions such as standardized randomization and study
criteria would greatly facilitate trial comparison in the future. Such
further studies will help us ensure we are better prepared not only for
annual influenza seasons but also for the ultimate pandemic," said
co-author Ira M. Longini, Jr., Ph.D., also a member of the Hutchinson
Center's Public Health Sciences Division and a biostatistics professor at
the University of Washington.
This research was partially supported by a National Institute of
Allergy and Infectious Disease grant and a National Institute of General
Medical Sciences MIDAS grant. Roche and GlaxoSmithKline allowed access to
the necessary data sets.
At Fred Hutchinson Cancer Research Center our interdisciplinary teams
of world-renowned scientists and humanitarians work together to prevent,
diagnose and treat cancer. Center researchers, including three Nobel
laureates, bring a relentless pursuit and passion for health, knowledge and
hope to their work and to the world. For more information, please visit
fhcrc.
BACKGROUND INFORMATION
About influenza
Influenza, commonly called the "flu," is a serious disease and annual
outbreaks and epidemics are caused by influenza A and B viruses. Influenza
is a highly contagious viral illness and is characterized by a sudden onset
of debilitating clinical symptoms that affect the entire body. Up to 500
million people are infected by influenza and up to 500,000 deaths are
attributed to influenza each year. Influenza complications occur in all
patient groups and include bronchitis, sinusitis, otitis media, and
pneumonia.
About oseltamivir and zanamivir
Oseltamivir (brand name Tamiflu) and zanamivir (brand name Relenza) are
neuraminidase inhibitors and are active against all clinically relevant
influenza viruses. They work by blocking the action of the neuraminidase
enzyme on the surface of the virus. When neuraminidase is inhibited, the
virus is unable to spread to and infect other cells in the body.
Oseltamivir is administered orally and is licensed for the treatment and
prevention of influenza in adults and in children aged 1 year and above.
Zanamivir is administered by oral inhalation. Zanamivir is registered in
the United States for the treatment of influenza in adults and children
aged 7 years or above, and for the prevention of influenza in adults and
children aged 5 years or above.
About the World Health Organization global influenza program:
who.int/csr/disease/influenza/en/
About the World Health Organization - avian flu:
who.int/mediacentre/factsheets/avian_influenza/en/
About the WHO Rapid Advice Guidelines on pharmacological management of
humans infected with avian influenza A (H5N1) virus:
who.int/csr/disease/avian_influenza/guidelines/pharmamanagement/
Fred Hutchinson Cancer Research Center
fhcrc/
View drug information on Relenza; Tamiflu capsule.
Комментариев нет:
Отправить комментарий