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Canada Communicable Disease Report
Volume 30 • ACS-2
1 March 2004
An Advisory Committee Statement (ACS)
National Advisory Committee on
Immunization (NACI)*
Update: Statement on Influenza Vaccination
for the 2003-04 Season
PDF
Version
6 Pages - 138 KB
Preamble
The National Advisory Committee on Immunization
(NACI) provides Health Canada with ongoing and timely
medical, scientific, and public health advice
relating to immunization. Health Canada acknowledges
that the advice and recommendations set out in this
statement are based upon the best current available
scientific knowledge and is disseminating this
document for information purposes. People
administering or using the vaccine should also be
aware of the contents of the relevant product
monograph(s). Recommendations for use and other
information set out herein may differ from that set
out in the product monograph(s) of the Canadian
licensed manufacturer(s) of the vaccine(s).
Manufacturer(s) have sought approval of the
vaccine(s) and provided evidence as to its safety and
efficacy only when it is used in accordance with the
product monographs.
The influenza season in Canada generally occurs
between November and April each year, and up to 25%
of the population may be infected in non-pandemic
years. Although serious complications of influenza
are most likely to occur in persons with certain
pre-existing medical conditions or those > 65
years of age, previously healthy young children may
have hospitalization rates comparable to those among
the elderly during influenza seasons(1).
Although influenza-related morbidity (physician
visits, otitis media, and lower respiratory tract
disease) is high in children(1,2), deaths
from influenza in children are rare.
The Canadian 2003-04 influenza season began earlier
than usual and involves a new variant of the A(H3N2)
strain (A/Fujian/411/2002) that is not included in
the current year vaccine. As with other H3N2
predominant seasons, this influenza season is
expected to be more severe than average, although
surveillance indicators to date are still within the
range of past seasons. In this update, NACI
summarizes the epidemiology of this year's influenza
season to date (week ending 20 December, 2003) on the
basis of data from the national FluWatch surveillance
program (http://www.phac-aspc.gc.ca/fluwatch/index.html)
and reaffirms its recommendations for annual
immunization programs published in August
2003(3).
Influenza Virus Surveillance
Influenza virus began circulating relatively early in
Canada this year compared with past seasons. For the
weeks spanning 24 August to 20 December, 2003,
sentinel laboratories tested 30 217 clinical
specimens for influenza; 4321 (14.3%) were positive.
The weekly percentages of clinical specimens that
were positive for influenza increased from 0.15% at
the start of this period to a peak of 21.4% during
the week ending 15 November, 2003. In previous years,
peaks in positive laboratory identifications
generally did not occur before mid-December. During
the 2000-01, 2001-02, and 2002-03 influenza seasons,
the peak percentages of specimens found to be
positive for influenza ranged from 12.8% to 26.0%.
During the 1999-2000 influenza season, a relatively
severe season when influenza A (H3N2) viruses
predominated, the peak weekly percentage of positive
specimens was 25%. It is still relatively early in
the current influenza season, and activity is just
beginning in many areas. Further peaks in positive
laboratory identifications for influenza are expected
to occur.
To date, of the 4321 positive influenza
identifications, 4309 (99.7%) were influenza A
viruses, and 12 (0.3%) were influenza B viruses. Of
the 4309 influenza A viruses, 374 (8.7%) have been
antigenically characterized so far by the National
Microbiology Laboratory; 347 (92.8%) are
A/Fujian/411/0(H3N2)-like viruses, 25 (6.7%) are
A/Panama/2007/99(H3N2)-like viruses, one (0.3%) is an
A/New Caledonia/20/9/9-like (H1N1) virus, and one
(0.3%) is an influenza A(H1N2) virus. As of 20
December, all provinces and territories except
Newfoundland and Labrador have reported
laboratory-confirmed influenza.
Over 50% of laboratory-confirmed influenza infections
reported to Health Canada this season have been
reported in children < 15 years of age. This
pattern in age distribution is expected, since as
influenza viruses change over time new strains are
more likely to infect young children, who are less
likely to have had previous exposure to influenza
viruses and, therefore, have limited protective
immunity. The relatively mild influenza seasons in
recent years may have contributed to the lack of
natural immunity in young children.
The A/Fujian/411/2002(H3N2)-like virus was the
predominant strain circulating in Australia and New
Zealand during the recent 2003 southern hemisphere
influenza season, and activity during this season was
relatively high in both countries(4). Many
countries in the Northern hemisphere, including the
United States, are experiencing the same predominance
of A/Fujian/411/2002(H3N2)-like viruses during the
current season(5). While influenza seasons
in which A(H3N2) viruses predominate are typically
associated with more severe illness and deaths, there
is insufficient evidence to date to determine whether
the A/Fujian-like viruses are more virulent that
other influenza A(H3N2) viruses(5).
Influenza-Like Illness (ILI)
Surveillance
For the weeks spanning 24 August to 20 December, the
weekly proportion of patient visits to approximately
200 sentinel providers nationwide for ILI increased
from 13 to 52 per 1000 patients seen. This is
consistent with typical influenza seasons, apart from
the early onset this season. During the 2000-01,
2001-02, and 2002-03 influenza seasons, the peak
weekly percentage of patient visits for ILI ranged
from 40 to 60 per 1000. During the 1999-2000 season,
the peak weekly percentage of patient visits for ILI
was 150 per 1000.
Influenza Activity Reported by Provincial and
Territorial Epidemiologists
Increasing influenza activity began in late September
and early October in Alberta, Saskatchewan, and the
Northwest Territories. Seasonal activity began next
in the Yukon, British Columbia, Ontario, and Nunavut.
The Atlantic provinces and Quebec were the last to
begin reporting influenza activity. Influenza
activity appears to have peaked in Alberta and
Saskatchewan by the week ending 22 November. During
the week ending 20 December, widespread activity was
reported throughout Ontario, while appearing to be on
the decline in the Territories, British Columbia, and
Saskatchewan. Activity is continuing to increase in
Quebec and Nova Scotia.
Reports of Severe Illness and Deaths in
Persons < 15 Years of Age
During annual influenza seasons, up to 10% to 25% of
the population may be infected, and attack rates of
over 30% have been estimated in children < 5 years
of age(2). Studies in the U.S. have shown
that previously healthy children < 1 year may have
hospitalization rates comparable to those in the
elderly during influenza seasons(1,2).
However, death from influenza in young children is
rarely reported.
At the end of October 2003, Health Canada requested
that provinces and territories report all
influenza-related deaths in children, after having
received reports of deaths from influenza A in
children in the United Kingdom and the United States
at the start of the season(6,7). To date,
Health Canada has received four reports of deaths
associated with laboratory-confirmed influenza A
infection in children < 15 years of age (range 7
to 14 years). Of these, three had an underlying
chronic illness and had received influenza vaccine
this season (one child was vaccinated > 2 weeks
before his/her presentation, one child was vaccinated
1 day before presentation, and the vaccination date
of the other case is unknown). The fourth death was
in a previously healthy child who had not been
vaccinated against influenza.
There is no real-time national reporting for
influenza-related hospitalizations or deaths in
Canada. Based on a retrospective review, 700 to 1000
hospitalizations due to influenza are reported in
children < 15 years of age each year, the majority
of these in children < 5 years of age. The average
number of reported deaths due to influenza in
children < 15 years of age, based on a
retrospective review of vital statistics (death
certificate) data from 1991 to 2000, is 2 per year
(range 0-5 per year). It is difficult to compare
historical data that are likely to underestimate
influenza-related deaths with the number of deaths
reported prospectively this season. It is likely that
there is increased awareness of severe complications
of influenza and increased reporting of
influenza-related deaths in children during the
current season. Recent reports from the U.S. suggest
that there is a wide range of influenza-associated
complications resulting in serious illnesses and
deaths in the pediatric population, and sudden deaths
associated with influenza may occur in previously
healthy children and adolescents(6,8).
Among the complications of influenza to date are
pneumonia and invasive bacterial co-infection.
Influenza Vaccine Recommendations
NACI reaffirms its recommendation for annual
immunization of persons at higher risk of serious
illness from influenza, including those > = 65
years of age; those > 6 months of age with cardiac
or pulmonary disease or chronic conditions such as
diabetes mellitus, cancer, immunodeficiency, or
immunosuppression (due to underlying disease and/or
therapy); and children > 6 months of age receiving
long-term acetylsalicylic acid (ASA) therapy. Vaccine
is also recommended for health care workers or others
(e.g. family members) in close contact with persons
who have underlying medical conditions(3).
While the priority for vaccine programs is persons at
highest risk of serious morbidity associated with
influenza, healthy adults and children can benefit
from protection from influenza and, as previously
stated by NACI(3), should also be
encouraged to receive vaccine. Children < 9 years
of age require two doses (dose for children 3 to 8
years old: 0.5 mL; for children 6 to 35 months old:
0.25 mL) 1 month apart if they have not been
immunized with influenza vaccine in a previous
season. Children < 6 months of age and persons
with severe allergy to eggs or to a previous dose of
influenza vaccine should not be vaccinated.
The A/Fujian-like viruses are drift variants of the
A/Panama/2007/99-like (H3N2) strain included in the
current 2003-2004 vaccine and were detected by global
surveillance early this year but too late for
inclusion in the current influenza
vaccine(9-11). Experimental testing of
ferrets using hemagglutination inhibition assays
indicates that antibodies to the A/Panama vaccine
virus cross-react with A/Fujian-like viruses;
therefore, current influenza vaccines should provide
some protection against A/Fujian-like
viruses(5). Early serologic studies to
assess cross-reacting antibodies have demonstrated
that adults and elderly persons immunized with
vaccines containing A/Panama/2007/99 develop
antibodies against A/Fujian/411/2002-like
viruses(11). However, the level of
protection against the A/Fujian-like viruses remains
uncertain until vaccine effectiveness studies for the
current year have been completed(5,11).
Since the current trivalent vaccines also contain
A/New Caledonia/20/99 (H1N1)-like and B/Hong
Kong/330/2001-like strains, they should offer
protection against these viruses if they circulate
during the rest of the season.
There has been an increase in demand for influenza
vaccine this season, over 10.2 million doses having
been distributed to provinces and territories by the
end of December 2003. To date, vaccine manufacturers
have been able to meet the demands of publicly funded
vaccine programs. However, the supply in the private
sector is likely to be low as available vaccines are
deemed to be a priority for the public programs.
In addition to immunization, infection control
measures are an effective means to interrupt
transmission of influenza virus. In particular,
careful hand hygiene and staying at home for those
who are febrile and unwell with respiratory symptoms
will prevent spread of infection(12,13).
In the health care setting the use of Routine
Practices and Additional Respiratory and Contact
Precautions with symptomatic patients is an effective
means of ensuring that respiratory infections are
contained(14). Use of the antivirals
amantadine, oseltamivir and zanamivir may be
appropriate in some clinical settings(3).
References
- Neuzil KM, Zhu Y, Griffin MR et al. Burden of
interpandemic influenza in children younger than 5
years: a 25-year prospective study. J Infect Dis
2002;185(2):147-52.
- Neuzil KM, Mellen BG, Wright PF et al. The effect
of influenza on hospitalizations, outpatient visits,
and courses of antibiotics in children. N Engl J Med
2000;342(4):225-31.
- National Advisory Committee on Immunization.
Statement on influenza vaccination for the 2003-2004
season. CCDR 2003;29(ACS-4):1-20.
- WHO Collaborating Centre for Reference &
Research on Influenza, Melbourne, Australia. Outbreak
of influenza reported throughout Australia. URL:
<http://www.influenzacentre.org/index.htm>.
Accessed 7 November, 2003.
- Centers for Disease Prevention and Control.
Update: influenza activity - United States, 2003-04
season. MMWR 2003;52(49):1197-1202.
- Centers for Disease Prevention and Control.
Update: influenza-associated deaths reported among
children aged < 18 years - United States,
2003-2004 influenza season. MMWR
2003;52(Dispatch):1-2. URL: <
http://www.cdc.gov/mmwr/preview/mmwrhtml/mm52d1219a1.htm>.
- Health Protection Agency. Current influenza
activity in the UK. Commun Dis Rep Wkly 2003;13(45).
URL: <
http://www.hpa.org.uk/infections/topics_az/influenza/seasonal/uk_data_sources.htm
>. Accessed 30 December, 2003.
- Centers for Disease Prevention and Control.
Severe morbidity and mortality associated with
influenza in children and young adults - Michigan,
2003. MMWR 2003;52:837-40.
- World Health Organization. Recommended
composition of influenza virus vaccines for use in
the 2003-2004 influenza season. Wkly Epidemiol Rec
2003;78:58-62. URL: <http://www.who.int/wer/2003/en/wer7809.pdf>.
- World Health Organization. Addendum to the
recommended composition of influenza virus vaccines
for use in the 2003-2004 influenza season. Wkly
Epidemiol Rec 2003;78:77. URL: <http://www.who.int/wer/2003/en/wer7811.pdf>.
- World Health Organization. Influenza vaccine for
the northern hemisphere 2003-2004: additional
information. URL: <
http://www.who.int/csr/disease/influenza/vaccine2003/en/index.html>.
Accessed 30 December, 2003.
- Hammond B, Ali Y, Fendler E et al. Effect of hand
sanitizer use on elementary school absenteeism. Am J
Infect Control 2000;28(5):340-46.
- White C, Kolble R, Carlson R et al. The effect of
hand hygiene on illness rate among students in
university residence halls. Am J Infect Control
2003;31(6):364-70.
- Health Canada. Routine practices and additional
precautions for preventing the transmission of
infection in health care. CCDR 1999;25(S4):1-142.
___________________________________
Members: Dr. M. Naus (Chairperson),
Dr. A. King (Executive Secretary), Dr. I. Bowmer, Dr.
G. De Serres, Dr. S. Dobson, Dr. J. Embree, Dr. I.
Gemmill, Dr. J. Langley, Dr. A. McGeer, Dr. P. Orr,
Dr. B. Tan, A. Zierler.
Liaison Representatives: S. Callery
(CHICA), Dr. J. Carsley (CPHA), Dr. T. Freeman
(CFPC), Dr. A. Gruslin (SOGC), A. Honish (CNCI), Dr.
B. Larke (CCMOH), Dr. B. Law (ACCA), Dr. V. Lentini
(DND), Dr. A. McCarthy (CIDS), Dr. J. Salzman
(CATMAT), Dr. L. Samson (CPS), Dr. D. Scheifele
(CAIRE), Dr. M. Wharton (CDC).
Ex-Officio Representatives: Dr. A.
Klein and Dr. H. Rode (BREC), Dr. R. Ramsingh
(FNIHB), Dr. T. Tam (CIDPC).
This statement was prepared by Drs. T. Tam and J.
Langley, and approved by NACI.
[Canada Communicable Disease
Report]
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