Structured Abstract
Please note: In 2003, the CTF updated its Grades of
Recommendations to include an "I Recommendation" for situations where
insufficient evidence exists to allow a recommendation to be made.
(Formerly, these situations were captured under a "C
Recommendation".) This change is not retroactive, and all
"C Recommendations" made prior to 2003 have not been
reevaluated in light of the new "I" recommendation grade. For a
discussion of these recommendation grades, please link to the 2003 article in
the Canadian Medical Association Journal here.
Prevention of Influenza
Prepared by R. Wayne Elford, MD, CCFP, FCFP, Director
of Research and Faculty Development, Department of Family Medicine, and
Michael Tarrant, MD, CCFP, FCFP, Associate Professor of Family Medicine,
University
of Calgary, Alberta
These recommendations were finalized by the Task Force in June 1993
Contents
Objective
To make recommendations about the prevention of influenza among general,
high-risk and health care provider populations in Canada. This updates
a 1979 report.
Burden
of Suffering
Influenza is the most important acute respiratory illness that causes adults
to seek medical care. Influenza A and B viruses are responsible, but mutate
with great regularity, resulting in new strains and subtypes of virus that
cause new epidemics almost annually. Current theories of influenza viral
epidemiology have not explained fully the persistence, seasonality, and
explosiveness of outbreaks over large geographical areas. Excess mortality
in the general population is one of the hallmarks of an influenza epidemic.
The age group over 65 years accounts for over 95% of the mortality associated
with influenza. The increased mortality and morbidity among persons over
65 years, is mostly due to the higher prevalence of chronic heart and lung
diseases in the elderly. The peak occurrence of hospitalizations of persons
with acute respiratory disease, usually pneumonia, coincides with the peak
of influenza virus activity each year. The magnitude of the problem is
compounded when the increase in sick-leave in health care providers coincides
with peak periods of hospitalization. The excess cost of sick-leave among
those of working age during influenza epidemic years exceeds that for all
other acute illnesses.
Options
Early detection of viral infection using a rapid diagnostic kit ("Directigen
Flu A test"). Other detection methods (clinical detection, isolation of
the virus and serological testing of antibody response) were briefly described.
Preventive measures included public awareness, isolation (to reduce
transmission), annual vaccination and chemoprophylaxis with amantadine.
Outcomes
Disease incidence, severity, duration, related mortality, clinical symptoms,
serum or secretory antibody response, immunologic memory, vaccination rate,
and positive and negative predictive values of the rapid diagnostic kit.
Evidence
A MEDLINE search of the years 1981 to 1992 using the MeSH headings influenza
virus, influenza vaccination and influenza chemoprophylaxis identified
155 citations. Reviews, editorials, commentaries and animal studies were
then excluded. Additional citations were identified from the bibliographies
of articles. If multiple articles on the same topic were found, those most
recently published and with the most rigorous designs were retained. Study
results were synthesized in table or graphic format only.
Recommendations were graded as:
|
A
|
Good evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
B
|
Fair evidence to support the recommendation that the condition
be specifically considered in a PHE. |
|
C
|
Poor evidence regarding inclusion or exclusion of the condition
in a PHE, but recommendations may be made on other grounds. |
|
D
|
Fair evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
|
E
|
Good evidence to support the recommendation that the condition
be specifically excluded from consideration in a PHE. |
Quality of evidence was rated according to 5 levels:
|
I
|
Evidence from at least 1 properly randomized controlled
trial (RCT). |
|
II-1
|
Evidence from well-designed controlled trials without randomization. |
|
II-2
|
Evidence from well-designed cohort or case-control analytic
studies, preferably from more than 1 centre or research group. |
|
II-3
|
Evidence from comparisons between times or places with
or without the intervention. Dramatic results in uncontrolled experiments
could also be included here. |
|
III
|
Opinions of respected authorities, based on clinical experience,
descriptive studies or reports of expert committees. |
Values
The 13-member Task Force of experts in family medicine, geriatric medicine,
pediatrics, psychiatry and epidemiology used an evidence-based method for
evaluating the effectiveness of preventive health care interventions. Recommendations
were not based on cost-effectiveness of options. Patient preferences were
not discussed.
Background papers providing critical appraisal of the evidence and tentative
recommendations prepared by the chapter author were pre-circulated to the
members. Evidence for this topic was presented and deliberated upon in
1- to 2-day meetings, 2 to 3 times per year from January 1993 to June 1993.
Consensus was reached on final recommendations.
Benefits,
Harms, and Costs
Positive predictive value of the "Directigen Flu A test" is 63% compared
with virus isolation. Negative predictive value is 100%. Reliability of
test results when conducted by non-laboratory trained persons is unknown.
Clinical trials show that vaccines are 70% to 80% effective in reducing
disease occurrence and related mortality in normal subjects when the vaccine
and viral strain are closely matched.
Data from cohort analytic studies support vaccination of elderly persons
living in institutions, persons with chronic heart or pulmonary conditions,
diabetes and those who are immunocompromised. In elderly persons, live-attenuated
vaccines offer no advantages over inactivated vaccines in terms of antibody
response or immunologic memory. Little evidence exists that adverse effects
of vaccination affect patient compliance. An RCT of vaccination of health
care providers reported a minimal reduction in symptoms. Although efficacious,
vaccination of the general population is not thought to be cost-effective.
2 RCTs demonstrated that outreach strategies (reminders, letter or telephone
contact) conducted in physicians’ offices increased the vaccination rate
among non-institutionalized adults at high risk.
Evidence from an RCT shows that amantadine is effective in preventing
influenza A illness, but not in preventing influenza B. It also shortens
the course of influenza A illness by 50% if administered within 48 hours
of symptom onset. Adverse effects, primarily gastrointestinal and central
nervous system symptoms, occur in about 40% of elderly patients with congestive
heart failure, high serum creatinine and multiple underlying diagnoses.
{3 studies have been published since this review which may have led
to different recommendations. These show benefits from vaccination for
healthy young adults [Nichol 1995], older adults [Govaert 1994], and, through
immunization of health care workers, for older institutionalized adults
[Potter 1997].}
Recommendations
Recommendation grade [A, B, C, D, E] and level of evidence
[I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations
in support of individual recommendations are identified in the guideline
text.
-
There is fair evidence to provide annual immunization with influenza vaccine
for high-risk groups (persons in institutions, >65 years, who are immunocompromised
or have chronic heart or pulmonary disease, diabetes mellitus) [B,
II-2]. and for
-
There is fair evidence to provide annual immunization with influenza vaccine
for health care providers [B,
I].
-
There is insufficient evidence to include or exclude (from the PHE) annual
immunization of the in the PHE of the general population £
65 years [C, III].
-
There is good evidence to include support outreach (e.g. nurse/physician
reminders) to high-risk groups [A,
I].
-
There is insufficient evidence to include or exclude use of rapid diagnostic
tests in suspected cases [C, II-1].
-
There is good evidence to include amantadine chemoprophylaxis of high-risk
or unvaccinated persons around exposed to an index case to reduce the spread
of infection [A, I].
Validation
This report was externally peer-reviewed. The National Advisory Committee
of the Bureau of Communicable Disease Epidemiology, Department of Health
and Welfare Canada (now Health Canada), the Immunization Practices Advisory
Committee (ACIP) of the U.S. Department of Health and Human Services and
the 1989 U.S. Preventive Services Task Force recommended immunization of
persons at high risk. The National Advisory Committee and the ACIP also
recommended amantadine to prevent illness and to reduce severity and duration
of illness.
Sponsors
The Canadian Task Force on Preventive Health Care
developed this guideline with funding from Health Canada.
Selected
References
Source Document
Other
-
Canadian Task Force on the Periodic Health Examination. The periodic health
examination. Can Med Assoc J. 1979;121:1193-1254.
-
Govaert TM, Thijs CT, Masurel N, et al. The efficacy of influenza vaccination
in elderly individuals. A randomized double-blind placebo-controlled trial.
JAMA. 1994;272:1661-5.
-
Nichol KL, Lind A, Margolis KL, et al. The effectiveness of vaccination
against influenza in healthy, working adults. N Engl J Med. 1995;333:889-93.
-
Potter J, Stott DJ, Roberts MA, et al. Influenza vaccination of health
care workers in long-term-care hospitals reduces the mortality of elderly
patients. J Infect Dis. 1997;175:1-6.
Link to Full Text of this
review
Link to Summary Table of Recommendations of this review
Link to Selected References list of this review
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