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Influenza A viruses periodically cause worldwide epidemics, or pandemics, with high rates of illness and death. A pandemic can occur at any time with the potential to cause serious illness, death, and extensive social and economic disruption throughout the world. Experts agree that future influenza pandemics are inevitable, but the timing and severity of the next pandemic cannot be predicted. Because there may be little warning, contingency planning is required to minimize the potentially devastating effects of an influenza pandemic.
In nature there are 16 different haemagglutinins and 9 different neuraminidases, which are two important surface glycoproteins of the influenza A virus. Influenza virus subtypes are named according to these “H” and “N” proteins. Although all 16 of the H types can infect birds, to date only H1, H2 and H3 have been associated with widespread human disease and H5, H7 and H9 have demonstrated the ability to cause human disease. It is important to recognize that as birds are the natural reservoir for these influenza viruses, occasionally people who have close contact with infected birds will become infected with novel viruses. Not all novel viruses however will evolve into pandemic viruses; nevertheless the pandemic potential of any new virus must be considered.
The following conditions are necessary for an influenza pandemic to occur:
Historic evidence suggests that pandemics have occurred three to four times per century. In the last century there were three influenza pandemics (“Spanish flu” during 1918–1919, “Asian flu” during 1957–1958, and “Hong Kong flu” during 1968–1969); these pandemics were separated by intervals of 11 to 44 years. The worst, during 1918–1919, killed an estimated 30,000 to 50,000 people in Canada and 20 to 50 million people worldwide. During each of the last three pandemics, the greatest increase in death rates occurred among persons less than 60 years of age; during 1918–1919, the greatest number of deaths occurred among those 20 to 40 years of age.
It is uncertain how the next human pandemic virus might arise. However pandemic viruses could arise through genetic mixing (reassortment) between human and avian influenza viruses and perhaps through cumulative mutations. The 1957 and 1968 pandemic viruses were reassortants of human and avian influenza virus genes. Pigs, which can be infected with both human and avian influenza viruses, may act as vehicles for reassortment events. In theory humans can also act as mixing vessels. Mounting evidence, including molecular sequencing, suggests that all 8 genes of the 1918 pandemic virus are avian in origin and the human pandemic potential was acquired through a series of mutations. Further studies are being carried out in order to gain a better understanding of the factors governing virulence and transmissibility of the 1918 pandemic influenza viruses.
Direct transmission of avian H5N1 influenza from chicken to humans was demonstrated during the 1997 Hong Kong “bird flu” incident. The spread of highly pathogenic avian influenza H5N1 in multiple countries in Asia since 2003 has been associated with sporadic human cases and a relatively high mortality rate. The H5N1 viruses identified in human cases have been wholly avian in genetic make up. The majority of new influenza strains emerge in Southeast Asia where large human populations have close interactions with pigs and domestic fowl. The probability of a new strain emerging in North America is thought to be relatively low.
An influenza pandemic is an inevitable event; however the timing and epidemiology of the next pandemic is unpredictable. In the development of this plan, several assumptions have been made in order to provide some estimates of potential impact and facilitate preparedness in Canada. These assumptions should not be interpreted as predictions for the next pandemic, but instead a reflection of current opinion regarding a reasonable scenario to guide planning activities. Pandemic plans need to be flexible in order be useful for a wide range of possible scenarios, recognizing that it is not feasible to completely plan for every possible pandemic scenario.
The key planning assumptions are listed below; planning principles and assumptions are also presented for each component of the Plan in the Preparedness Section. In addition several of the key assumptions have been repeated in Annex M, Public Health Measures, where the recommended actions are linked to these and other more specific assumptions. These assumptions were developed based on information from a review of past pandemics and published reviews of other international plans. The assumptions regarding absenteeism are based on an analysis recently completed by the Department of Finance Canada.
The following assumption and explanation have been provided by the Department of Finance (federal), Economic Analysis and Forecasting Division, Based on work completed as of September 2006.
Care of Sick
|PrudenceTable 1 - Footnote 1 *||Total|
|Forestry, Fishing, Mining, Oil and Gas||9.9||3.4||4.7||18.0|
|Transportation & Warehousing||9.5||5.0||5.9||20.4|
|Finance, Insurance and Real Estate||7.2||6.3||6.6||20.1|
|Professional, Scientific and Technical Services||6.3||6.1||6.2||18.6|
|Healtd Care and Social Assistance||11.1||6.3||8.2||25.6|
|Information, Culture and Recreation||3.8||5.7||6.3||15.8|
|Accommodation and Food Services||6.4||6.3||6.5||19.2|
The impact of the next influenza pandemic is difficult to predict; it depends on how virulent the virus is, how rapidly it spreads from population to population, and the effectiveness of prevention and response efforts. Estimates of health and economic impacts are important to guide public health policy decisions and to guiding pandemic planning in the health and emergency sectors.
During “normal” influenza epidemics that occur almost every winter in North America, an average of 10% to 25% of the population becomes ill resulting in an average of 4,000 deaths and 20,000 hospitalizations. During severe influenza A epidemics, 30% to 50% of the population may become ill resulting in 6,000 to 8,000 deaths and 30,000 to 40,000 hospitalizations. The highest rates of infection and clinical illness occur in children but serious complications and death occur mainly in the elderly.
During a pandemic, historic data shows that over 70% of a population may become infected with the novel virus and the age-specific morbidity and mortality may be quite different from the annual epidemics. During the 1918–1919 pandemic, young adults had the highest mortality rates, with nearly half of the influenza-related deaths occurring among persons 20 to 40 years of age. During the 1957–1958 and 1968–1969 pandemics in the United States, persons over 65 years of age accounted for 36% and 48% of influenza-related deaths respectively.
An estimate of the health and economic impacts of a pandemic in Canada was performed in 1999 using a model developed by Meltzer and colleagues, United States Centers for Disease Control and Prevention, Atlanta, Georgia, (available at http://www.cdc.gov/ncidod/eid/ vol5no5/meltzer.htm). The assumptions in this model are based on American epidemiologic data on various mutually exclusive population health outcomes (death, hospitalization, outpatient treatment, and ill but with no formal care) for severe annual influenza A epidemics and data from the most recent pandemics (i.e., not the 1918-1919 pandemic). For planning purposes we consider the estimates from this model to reflect a “mild to moderate” scenario in terms of severity of illness. Recently, projections have been made based on a more “severe” scenario. In the severe scenario it is estimated that 2% of clinical cases will die and 10% will require hospitalization for management of their illness. While these higher estimates, which are considered to be more consistent with the outcomes of the 1918-1919 pandemic have been used to describe potential impact of a severe pandemic, to date the emphasis has been on national planning for a pandemic of moderate severity.
The Meltzer model does not include the potential impact of antivirals drugs, public health measures, or an effective vaccine. These estimates, therefore, may over-estimate the potential impact in Canada; they are provided here for planning purposes only and to raise awareness regarding potential health impacts. It is also important to recognize that as the age distribution of the Canadian population changes over time the potential health impacts will also vary. If the age-specific mortality rates remain highest for the age groups on either end of the age spectrum with the elderly having a higher rate than young children (i.e., the typical annual skewed “U-shaped” mortality curve), then as the population ages the potential number of deaths when a pandemic strikes may be higher than projected in this document.
Based on the 1999 analysis using the Meltzer model, during a pandemic of “mild to moderate” severity an estimated 4.5 to 10.6 million Canadians would become clinically ill such that they would be unable to attend work or other activities for at least a half a day (Table 1). This proportion, which represents 15% to 35% of the population, does not include individuals who contract the virus and feel ill but continue their usual activities. In addition, it is estimated that between 2.1 and 5.0 million people would require outpatient care, between 34 thousand and 138 thousand people would be hospitalized and recover, and between 11 thousand and 58 thousand people would die in Canada during an influenza pandemic (Table 2). It is important to note that since these are discrete outcomes the number of people hospitalized during the pandemic will include the entire “hospitalized and recovered” group and those that died in hospital which is expected to be a large proportion of the fatal cases. Moreover, these outcomes would occur as a result of relatively short (6-8 week) pandemic waves, highlighting the intense impact of pandemic influenza compared to other illnesses. These numbers are estimates and do not take into account the differences in the health care systems, practice patterns and health care-seeking behaviour in Canada as compared to the United States or changes in the age-distribution within Canada since 1999; nonetheless, they provide a picture of the magnitude and potential impact of the next influenza pandemic. Canadian estimates of resource use for patients with these health outcomes and Canadian resource unit costs were applied to provide and estimate of Canadian costs based on this American model. The economic impacts of the health outcomes (direct and indirect) on the health care system and on society were estimated to be between CAN$10 to 24 billion in 1999. This estimate does not include other societal impacts such as those on trade and tourism.
(based on Canadian Population: 30,301,180)
|Attack Rate 15%||Attack Rate 35%|
|Mean number||5th Percentile||95th Percentile||Mean number||5th Percentile||95th Percentile|
|DeathTable 2 - Footnote 1 *||17,768||10,544||24,954||41,459||24,603||58,227|
|Hospitalization with recovery Table 2 - Footnote 1 *||46,639||34,042||59,166||108,824||79,431||138,053|
|Ill, no formal care||2,394,443||2,335,458||2,455,967||5,587,035||5,449,401||5,730,591|
On April 8, 2005, the World Health Organization (WHO) released an updated version of its 1999 guidance on pandemic planning and preparedness. This new document, WHO global influenza preparedness plan: The role of WHO and recommendations for national measures before and during pandemics, (available online at: http://www.who.int/csr/resources/publications/influenza/WHO_CDS_CSR_GIP_2005_5.pdf) contains WHO and national activities organized using new pandemic phase terminology.
To facilitate consistency with the WHO phases and to tie in a descriptor of national levels of novel influenza subtype activity in Canada, the revised nomenclature for Canadian pandemic phases is as follows:
WHO Global Phase. Canadian Activity Level (example: 3.0)
The WHO Phase number reflects the international risk or activity level with respect to the new influenza virus subtype virus (i.e. Phases 1 to 6) and is determined by the WHO. The Canadian activity level indicator noted after the decimal point would likely be determined by the Pandemic Influenza Committee (PIC) and/or the Public Health Agency of Canada (PHAC) and would summarize the observed new influenza virus subtype activity in Canada. It is proposed that these levels be classified as follows:
Localized and widespread activity have been combined in one “level” since the response activities associated with these two categories are not sufficiently different to warrant distinguishing between them.
For consistency with the WHO terminology, it was also agreed that the general categories of Interpandemic Period, Pandemic Alert Period, Pandemic Period and Post-Pandemic Period be adopted and used in public communications.
During the Interpandemic Period (Phases 1 to 2), new emphasis is placed on addressing human health risks posed by animal outbreaks. The Pandemic Alert Period (Phases 3 to 5) now addresses the situation of evolution or adaptation of a novel animal influenza virus with pandemic potential. It places greater emphasis on rapid intervention in an attempt to contain or delay the spread of a new influenza virus subtype in humans. Although it is uncertain if such “containment” measures would be effective or feasible, it is still useful to consider potential early interventions for planning purposes.
Note: The phase terminology used reflects the epidemiological situation and the key objectives of the pandemic response but does not necessarily reflect the level of activation of emergency operations within Canada.
|Phase||Definition||Example(s)||Corresponding former Canadian and WHO Global Phases (1999)|
|1.0||No new virus subtypes have been detected in humans. An influenza virus subtype that has caused human infection may be present in animals located outside of Canada. If present in animals, the risk of human infection and/or disease is considered to be low.||Highly pathogenic H7N3 detected in poultry outside of Canada||Canada: Phase 0, Level 0 Global: Phase 0, Level 0|
|1.1||No new virus subtypes have been detected in humans. An influenza virus subtype that has caused human infection is present in animals in Canada but the risk of human infection and/or disease is considered to be low.||Highly pathogenic H7N3 detected in a poultry flock in Canada||Canada: Phase 0, Level 0 Global: Phase 0, Level 0|
|2.0||No new virus subtypes have been detected in humans. However, an animal influenza virus subtype that poses substantial risk to humans is circulating in animals located outside of Canada.||Highly pathogenic H5N1 detected in poultry flocks outside of Canada||Canada: Phase 0, Level 0 Global: Phase 0, Level 0|
|2.1||No new virus subtypes have been detected in humans. However, an animal influenza virus subtype that poses substantial risk to humans is circulating in animals in Canada.||Highly pathogenic H5N1 detected in poultry flocks in Canada||Canada: Phase 0, Level 0 Global: Phase 0, Level 0|
|Phase||Definition||Example(s)||Corresponding former Canadian and WHO Global Phases (1999)|
|3.0||Outside Canada human infection(s) with a new subtype are occurring, but no human-to-human spread or, at most, rare instances of spread to a close contact has been observed. No cases identified in Canada.||Outside Canada sporadic human cases are occurring in connection to an avian outbreak.||Canada: Phase 0, Level 0 Global: Phase 0, Level 1 or Phase 0, Level 2 if more than one human case|
|3.1||Single human case(s) with a new subtype detected in Canada. The virus is not known to be spreading from human-to-human or, at most, rare instances of spread to a close contact have been observed.||Case imported into Canada from area outside Canada experiencing an avian outbreak. Case arising in Canada “de novo” or in association with an avian outbreak in Canada.||Canada and Global: Phase 0, Level 1 or Phase 0, Level 2 if more than one human case|
|4.0||Outside Canada small cluster(s) with limited human-to-human transmission are occurring but spread is highly localized, suggesting that the virus is not well adapted to humans. No cases identified with these cluster(s) have been detected in Canada.||Outside Canada small cluster(s) of human cases with a novel virus are occurring in connection to an avian outbreak.||Canada: Phase 0, Level 0 Global: Phase 0, Level 3|
|4.1||Single human case(s) with the virus that has demonstrated limited human-to-human transmission detected in Canada. No cluster(s) identified in Canada.||Detection of an imported case in Canada that is infected with the novel virus known to be causing small clusters of human cases outside Canada.||Canada and Global: Phase 0, Level 3|
|4.2||Small localized clusters with limited human-to-human transmission are occurring in Canada but spread is highly localized, suggesting that the virus is not well adapted to humans.||Detection of a localized cluster of cases in Canada linked to an imported case or from cases arising in Canada.||Canada and Global: Phase 0, Level 3|
|5.0||Outside Canada larger cluster(s) are occurring but human-to-human spread still localized, suggesting that the virus is becoming increasingly better adapted to humans but may not yet be fully transmissible (substantial pandemic risk). No cases identified with these clusters have been detected in Canada.||Outside Canada larger cluster(s) of human cases with a novel virus are occurring.||Canada: Phase 0, Level 0 Global: Phase 0, Level 3|
|5.1||Single human case(s) with the virus that is better adapted to humans detected in Canada. No cluster(s) identified in Canada.||Detection of an imported case in Canada that is infected with the virus known to be causing larger clusters of human cases outside Canada.||Canada and Global: Phase 0, Level 3|
|5.2||Larger localized cluster(s) with limited human-to-human transmission are occurring in Canada but human-to-human spread still localized, suggesting that the virus is becoming increasingly better adapted to humans but may not yet be fully transmissible (substantial pandemic risk).||Detection of a large but localized cluster of cases in Canada linked to an imported case OR from cases arising in Canada.||Canada and Global: Phase 0, Level 3|
|Phase||Definition||Example(s)||Corresponding former Canadian and WHO Global Phases (1999)|
|6.0||Outside Canada increased and sustained transmission in the general population has been observed. No cases have been detected in Canada.||Countries outside of Canada have reported sustained transmission of the new virus in their populations.||Canada: Phase 0, Level 0; Global: Phase 1|
|6.1||Single human case(s) with the pandemic virus detected in Canada. No cluster(s) identified in Canada.||Detection of an imported case in Canada that is infected with the pandemic virus.||Canada and Global: Phase 1|
|6.2||Localized or widespread pandemic activity observed in the Canadian population.||Large numbers of clinical cases being rapidly identified in Canada with no history of travel to an affected area.||Canada and Global: Phase 1, 2 or 4|
The new Canadian phase terminology does not include Canadian phases that would denote the end of the first pandemic wave, the interval between waves or the onset of a second pandemic wave. It is expected the Canadian Phase will reflect the highest level of activity occurring in Canada (using the .0, .1 or .2 nomenclature) and that additional details regarding pandemic waves will accompany this communication. Regional and local influenza activity will be communicated as sporadic, localized or widespread; these terms are similar to current national surveillance (FluWatch) terminology.
A recovery period (Phase 5 in the 1999 WHO document) would be expected to occur following Phase 6 (i.e. the Pandemic Period) after which there would be a return to the Interpandemic Period (e.g. Global Phase 1 or 2). Indicators for the return to the Interpandemic Period will be likely based on epidemiologic indicators (e.g. the return of annual fall–winter cycle of influenza activity) rather than on a “return to normal” of societal or economic indicators.
The WHO has indicated that, in the event of concurrent circulation of two or more new influenza virus subtypes globally, the declared phase will reflect the highest level of risk for a pandemic. The PIC has also decided to use this strategy. For example, if H5N1 is causing sporadic human illness in Asia but no cases have been detected in Canada, the Canadian Phase would be 3.0. Subsequently, if a domestic avian outbreak of H7N3 occurs in Canada at the same time, it will be stated that Canada is in Phase 3.0 due to the H5N1 virus but is also responding to the occurrence of an avian outbreak caused by H7N3. The Canadian Phase would always reflect the status in Canada with respect to the virus with the highest pandemic risk, regardless of whether that virus is present in or outside of Canada.
The legal considerations that arise in the context of pandemic preparedness and response are varied and complex. Given that pandemic influenza is a global concern, planning and preparation requires the coordianted efforts of all levels of government within Canada in addition to international cooperation. It is important to recognize, therefore, that international laws as well as federal and provincial/territorial legislation may be needed to effectively respond to an influenza pandemic.
At the international level, the International Health Regulations (IHRs) provide a legal framework under WHO to protect against and control the international spread of disease while avoiding unnecessary interference with international traffic and trade. The revised IHRs (available at: http://www.who.int/csr/ihr/en/) substantially update the 1969 IHRs that addressed the potential spread of only three diseases: yellow fever, plague and cholera. They also establish a more effective and transparent process to be followed by WHO and states for determining and responding to a public health emergency of international concern (PHEIC). Most importantly, it broadens the scope of international collaboration to include any existing, re-emerging or new disease that could represent a threat internationally.
New provisions in the revised IHRs include obligations for:
In accordance with the IHRs, there are obligations at all levels of governments. In Canada, provinces and territories would use established protocols to report influenza infections of international concern to PHAC (national focal point) and then PHAC would report potential pandemic flu to WHO.
Public health ethics is a new area of inquiry that aims to identify the underlying values and principles that inform public health interventions. It has been noted that "public health ethics requires that public health improvement come through just and respectful means".Footnote 1 In Canada, ethics has increasingly informed health policy.Footnote 2 Ethical analysis helps to identify in a logical and transparent way how to “do the right thing@. Clearly, this is not always easy, as there may be conflicting ethical principles as well as other factors, such as regulations, scientific evidence and comparable policies in other countries, which must be taken into account. In this section, some of the emerging public health ethics principles that have influenced the development of the Canadian Pandemic Influenza Plan (CPIP) for the Health Sector are identified.
Pandemic influenza involves the entire health system, so it is important to consider how clinical ethics and public health ethics intersect. Clinical ethics is focussed on the health and interests of an individual. In contrast, public health ethics is focussed on the health and interests of a population. In an effective health system, these interests are in a dynamic balance. Seminal values in public health ethics are justice and respect for the individual. This reflects the assumption that a population can be healthy only with the collective support of the many individuals within that population. This support arises from the recognition that it is in an individual's best interest to be part of a healthy population.
The importance given to individual and collective interests will shift according to the nature of the health risk being addressed. When a health risk primarily affects an individual, clinical ethics will predominate and a high value will be placed on individual interests. When a health risk affects a population, however, public health ethics will predominate and a high value will be placed on collective interests. For example, during an infectious disease outbreak the public's health is at risk, and thus collective interests will prevail and individual interests may be temporarily affected (such as limitation of travel). Given the foundational values of justice and respect for individuals, public health ethics helps to identify why, when and how to exercise collective interests for the public good.
The organizing principle of public health ethics is the goal of public health itself: to protect and promote the public's health. This organizing principle is reflected in the Plan's two goals: to minimize morbidity and mortality and to minimize societal disruption. The health protection principle is exemplified in the basic strategies identified in the CPIP: detection and surveillance, public health measures, early treatment with antiviral medications, emergency management, and vaccine development. The health promotion principle is addressed through a well-thought out, nationally coordinated communications strategy that informs the public of the risk from a pandemic, and identifies infection control practices that everyone should adopt.
The debates in public health ethics have not centred around the need to protect and promote the public's health, but rather on the means by which to do this. Specifically, one of the greatest debates in pandemic planning has been around the issue of resource allocation. For example, given that 30 million doses of a pandemic vaccine cannot be made available to everyone at the same time, who will get what by when? The ethical principle that has guided these discussions is distributive justice. Distributive justice implies the distribution of resources in a fair and equitable manner based on need. This principle underlies the recommendation that health care workers form a priority group for the vaccine. However, how the distribution is done is important. Discussions on resource allocation that address the hard realities of limited resources bring into focus a seminal ethical principle adopted by public health ethics: respect for the inherent dignity of all persons.Footnote 3 This means that although some people may not be eligible for a vaccine initially, they need to be informed and cared for in a way that is respectful and maintains their dignity. This principle will need to inform the allocation of all scarce resources during a pandemic.
Another major debate in public health ethics, is what to do when the promotion of the public's health occurs at the price of individual freedom. Autonomy is a highly valued principle in bioethics yet this can be at odds with protecting the public's health. One principle that has been developed to address this is the principle of least restrictive means.Footnote 4 This principle stipulates that personal autonomy should be infringed upon only to the extent necessary to ensure the public good. This is illustrated in certain provincial public health laws. For example, during SARS public health officers quarantined those who may have been exposed to the SARS virus. This is considered to be a justifiable, temporary limitation of personal autonomy in the interests of limiting the spread of a specific communicable disease.
Other principles in public health ethics helped to inform the Canadian Pandemic Influenza Plan: specifically the need to optimize the risk/benefit ratio of any interventions and to maintain transparency and public accountability in public health decision-making. Optimizing the benefit/risk ratio means that the benefit of any proposed intervention needs to be maximized and the risks minimized. Benefit is assessed largely by evidence of efficacy; risk by anticipating any untoward effects of an intervention. However other factors, such as costs, feasibility, legal requirements and Canadian values also need to be factored in. Conducting a careful risk benefit assessment helps public health professionals ensure excellence. This principle also means decisions may need to be revised in the light of new information on risks or benefits. For example, in the 2004 Plan priority groups were identified for both antiviral treatment and prophylaxis. Based on evidence made available since that time, the decision was made to expand our antiviral stockpile, adopt an early treatment for all who need it strategy and conduct a full review of the prophylaxis issue, including public consultations.
Finally, the principles of transparency and accountability have also informed this Plan. Public health decisions should be publicly justifiable, and as such should be open to public review. The need for transparency and accountability are reflected in the planning process and the public access to the plan itself.
In summary, the principles of public health ethics have informed both the goals of this Plan, and the manner in which those goals should be realized. These principles create a very high standard for public health interventions. A number of ethics-related initiatives are underway both within government and within the academic sector.Footnote 5 These initiatives will advance the new field of public health ethics and inform future editions of the Plan.
Summary of the ethical principles informing the Canadian Pandemic Influenza Plan for the Health Sector (2006)