What Health Professionals need to know about pandemic influenza

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Background

While there are four types of influenza virus (A, B, C and D), only influenza A viruses have been known to cause pandemics. Influenza pandemics occur when an influenza A virus to which most humans have little or no immunity acquires the ability to cause sustained human-to-human transmission, leading to community-wide outbreaks and spreading rapidly worldwide.

These novel influenza viruses may arise through genetic reassortment (animal and human influenza genes mix together) or genetic mutation (genetic changes in an animal influenza virus, allowing it to easily infect humans). Pigs can become infected with influenza viruses from different species, such as birds, acting as a "mixing vessel" to facilitate the reassortment of genes from different viruses.

Aquatic birds are the natural hosts for influenza A viruses, although a wide range of species can be infected and significant disease outbreaks can occur in poultry, pigs and other species. Most of these animal influenza strains do not cause disease in humans except occasionally when humans have close contact with infected animals.

Not all novel influenza viruses evolve into pandemic viruses. Some novel subtypes, like the avian A (H5N1) virus, have caused sporadic human influenza cases but have not gained the ability to spread easily in humans. As the overall human case fatality rate for A (H5N1) infections has been over 50%, there are concerns about the potential of a high impact human pandemic if this virus gains the capacity to spread easily in people.

What are the typical characteristics of pandemics?

  • the pattern of disease is different in pandemics than in seasonal influenza
  • pandemics may arrive outside of the usual influenza season and typically have more than one wave of illness
  • the total duration of a pandemic is likely to be 12 to 18 months
  • the new pandemic virus replaces other circulating influenza strains. Afterwards, the pandemic strain becomes part of (and may dominate) the mix of seasonal influenza A viruses
  • during seasonal influenza, most hospitalizations and deaths occur in the elderly and persons with underlying health conditions, whereas, in a pandemic, disproportionately more severe disease and death is seen in young people and in persons without underlying health conditions
  • there is a gradual reversion back to the typical seasonal morbidity and mortality pattern over the decade following the pandemic

Unpredictable nature of pandemics

Influenza is unpredictable. Every influenza season and every pandemic is different. These uncertainties make pandemic planning challenging and highlight the need for flexibility and adaptability.

When and where will the next pandemic occur?

Although historically pandemics have occurred three to four times per century, there is no predictable interval.

An influenza pandemic could emerge anywhere in the world, and there may be very little lead time before Canada is extensively involved. While most seasonal influenza strains emerge in East/Southeast Asia, the same is not true for pandemic influenza; the 2009 pandemic emerged in North America.

How will the pandemic spread?

Pandemics often first arrive outside the usual influenza season (e.g., in late spring or summer) and typically have more than one wave of infection. However, this is not true in all circumstances or in all areas. A small first wave is often followed by a larger second wave, but the relative size of pandemic waves may vary. The speed of spread may also vary - pandemic waves can be intense or more spread-out over time. An intense wave would put more stress on the health care system.

What will be its characteristics?

The basic characteristics of the next pandemic virus are unknown, including its antigenic type (e.g., H2, H5, H7), its transmissibility and virulence, and the populations most affected.

Will seasonal influenza interventions be effective for pandemic influenza?

Typical seasonal influenza interventions are expected to be effective during the pandemic. However, the novel virus could be resistant to antiviral medications and/or pandemic vaccine production could be delayed or unsuccessful. The extent of vaccine uptake and adoption of public health measures is also unknown.

Pandemic impact

For Canada's pandemic planning purposes, the term pandemic "impact" (i.e. low, moderate or high impact) is used rather than pandemic "severity" when referring to the effects of a pandemic on a population.

Pandemics vary in their impact, as do seasonal influenza outbreaks, although usually on a higher scale of magnitude. As such, Canada needs to be prepared for a wide range of pandemic scenarios, with impacts varying from low to high:

  • Low impact pandemic might resemble moderate to severe seasonal influenza outbreaks, although its epidemiological profile would be different in important ways. This scenario involves an influenza virus with low transmissibility and low virulence. It might be expected to stress health care services.
  • Moderate to high impact pandemic could result in high rates of illness and death across the country, create severe challenges for the health care sector, and could disrupt the normal functioning of society. People with limited resources and support systems could be put into a more vulnerable state.

There are many factors that can affect pandemic impact, such as virus transmissibility and virulence, population vulnerability (e.g., pre-existing population immunity, presence of underlying health conditions), effectiveness of interventions (e.g., vaccine, antiviral medications, public health measures), the health care system response, and risk communications. Also important is the extent of public adoption of desired behaviours (e.g., practicing hand hygiene and respiratory etiquette, staying home when ill) and social mobilization.

Pandemic planning in Canada

Pandemic planning activities in Canada began in the 1980s. Pandemic vaccine preparedness contracts have been in place since 2001. The Canadian Influenza Pandemic Plan for the Health Sector was first published in 2004. In 2009, Canada's pandemic preparedness planning efforts were tested for the first time, with the emergence of the influenza A (H1N1) pandemic.

Many valuable lessons were learned from this experience, including recognition of the value of building on seasonal influenza surveillance and control measures.

The updated Canadian Pandemic Influenza Preparedness: Planning Guidance for the Health Sector (CPIP) provides planning guidance for the federal, provincial and territorial health sector. It is based on a risk management approach and allows for a more flexible and adaptable response to future pandemics. CPIP is primarily for federal, provincial and territorial health ministries; however, it also serves as a reference document for health-related organizations and other stakeholders. Although the CPIP provides strategic guidance and a framework to support consistent and coordinated pandemic preparedness and response across jurisdictions, provinces and territories have the ultimate responsibility for planning and decision-making within their respective jurisdictions.

Health care providers can learn more about the pandemic plan of the province or territory in which they practice.

Key components of Pandemic Influenza preparedness and response

Surveillance

Canada participates in national and international surveillance activities to monitor for and detect the spread of seasonal influenza, animal influenza, and emerging respiratory pathogens.

FluWatch is the national influenza surveillance system that monitors the spread of flu and flu-like illnesses on an on-going basis. FluWatch also provides early detection and timely up-to-date information on influenza activity in Canada. The National Microbiology Laboratory (NML), Canada's leading public health infectious disease laboratory, receives a portion of the influenza positive specimens from provincial laboratories for strain characterization and antiviral resistance testing.

Canada's surveillance systems for seasonal influenza vaccine safety would be leveraged during a pandemic. Enhanced surveillance activities may be needed during a pandemic, such as targeted surveillance in remote communities, seroprevalence studies, and pandemic vaccine effectiveness studies.

Emerging respiratory pathogens include either new variants of known respiratory pathogens (e.g., influenza A (H3N2) or emergence of newly identified (e.g., avian influenza A (H7N9)) or unknown pathogens.

Health care providers have a crucial role in the detection and reporting of emerging respiratory pathogens and severe acute respiratory infection.

Detailed information about pandemic influenza surveillance can be found in the CPIP.

Laboratory

Laboratory testing during a pandemic supports public health surveillance by monitoring the geographic spread and epidemiological trends of the pandemic, monitoring antiviral resistance, facilitating clinical management, and supporting studies of vaccine effectiveness.

The Canadian Public Health Laboratory Network (CPHLN) is a national association of public health laboratory professionals with the mandate to ensure early detection of infectious diseases and facilitate a timely and coordinated response through its network. CPHLN will support public health and diagnostic laboratories by providing recommendations and best practices for specimen collection and testing for the novel influenza virus. The NML will share protocols, reagents and proficiency panels to ensure that test methods are capable of detecting the new virus. Molecular testing is the primary method used for the diagnosis of influenza.

In the event that a novel pathogen is detected, Canada collaborates with the international community through the International Health Regulations, which protect global public health from the spread of infectious diseases such as novel influenza A viruses.

Detailed information about pandemic influenza laboratory planning can be found in the CPIP.

Vaccine

Immunization of susceptible individuals is the most effective way to prevent disease and death from influenza. The overall impact of the pandemic vaccine strategy will depend on vaccine effectiveness and uptake, as well as the timing of vaccine availability in relation to pandemic activity. Using current technologies, it takes four to six months to develop and produce pandemic vaccine, so it is not likely to be available by the time the first pandemic wave reaches Canada. Furthermore, it will become available in stages, which may require prioritization of initial pandemic vaccine supply.

The first pandemic vaccine contract was awarded in 2001 and was used to provide Canada's vaccine supply during the 2009 influenza pandemic. In 2011, Canada entered into a new ten-year contract for pandemic influenza vaccine supply to ensure that there is rapid and priority access to a supply of adjuvanted pandemic influenza vaccine produced in Canada. Canada also arranges for a separate secondary supply of vaccine.

National recommendations for the use of pandemic vaccine, including the priority groups for initial supplies, will be provided by the National Advisory Committee on Immunization.

Each province and territory is responsible for distributing and administering the vaccine to its residents.

Other key elements of Canada's pandemic vaccine strategy, such as monitoring of vaccine uptake and safety, will leverage the infrastructure already in place for seasonal influenza immunization programs.

Detailed information about pandemic influenza vaccine can be found in the CPIP.

Antiviral

Antiviral medications are used to treat persons with influenza illness or to prevent influenza in exposed persons. They are the only influenza-specific intervention that can be used to mitigate the impact of a pandemic before vaccine becomes available.

Canada's antiviral strategy includes federal, provincial and territorial stockpiles of antivirals for use in the event of an influenza pandemic, primarily for early treatment and for outbreak control in closed health care facilities (e.g., long-term care facilities, hospitals). Early treatment of influenza cases, preferably within 48 hours, is recommended in order to reduce the severity and duration of illness, particularly the occurrence of influenza-related complications, hospitalization and death.

Clinical guidelines have been developed for antiviral use for seasonal influenza by the Association of Medical Microbiology and Infectious Disease Canada. Similar guidelines will be provided for pandemic influenza when the next pandemic occurs.

Detailed information about pandemic influenza antiviral planning can be found in the CPIP.

Public health measures

The public health response to a pandemic includes the implementation of non-pharmaceutical measures, such as the promotion of individual strategies (e.g. coughing into your sleeve, handwashing) and social distancing (e.g. staying at home when you are sick) to reduce disease spread in the home and community. Other public health measures could include restricting mass gatherings (e.g. concerts) or school closures. In a pandemic, the measures recommended will depend on the impact of the pandemic and may change as epidemiological information emerges.

Additional details about pandemic public health measures can be found in the CPIP.

Health care services

All parts of the health sector, including public health, will be under stress during a pandemic. Advance planning, training and exercises will greatly assist in handling this increased demand on health services, staffing, resources and supplies and in providing the best possible clinical outcomes for persons ill with influenza.

Continuity of operations and surge capacity planning are key components of health sector preparation, together with strong infection prevention and control and occupational health programs within each organization that provides health services.

In planning for the delivery of health services, it is important to encompass the entire continuum of care from outpatient care to acute care to long-term care, and to include community health partners.

Further information about Health Care Services coordination during a pandemic can be found in CPIP.

Communications

Communication of information and advice is often the first and most important public health intervention during an emergency. Health care providers will be engaged in two-way dialogue to help ensure that products and messages meet their needs for timely, clear, concise and relevant information. During an influenza pandemic, health care providers will be able to access timely and trusted information and guidance from Canada.ca/flu as well as provincial and territorial governments' web sites and social media channels.

Further information about communicating during a pandemic can be found in CPIP.

Research

Research plays a key role in addressing knowledge gaps about the influenza virus and effective prevention, treatment and control for both seasonal and pandemic influenza.

Some research can be carried out between pandemics, but some can only be conducted during a pandemic. Networks that are created to conduct research in between pandemics are well placed to rapidly facilitate pandemic research. For example, the Canadian Immunization Research Network, a national network of key vaccine researchers, will be active in ongoing influenza vaccine research projects.

Further information about research during a pandemic can be found in CPIP.

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