Canada Communicable Disease Report

Final Report of Outcomes from the National Consensus Conference for Vaccine-Preventable Diseases in Canada

June 2005

Disease Summaries

Influenza

Background

The purpose of this session was to develop updated goals and recommendations for influenza immunization in Canada, based on a review of current issues and the outcomes from the 1993 National Influenza Consensus Conference and a 2001 meeting on the role of vaccines in influenza control. Below are highlights of presentations on influenza immunization initiatives and challenges in Canada and the US.

Immunization in the US:

(Dr. Nancy Cox, CDC)

Young children have become a new focus of CDC influenza immunization efforts, as they have been determined to have an increased risk for influenza-associated hospitalization. In 2004, annual immunizations were recommended for all children 6 to 23 months, a newly designated high-risk group.

The challenges of vaccine production were subsequently reviewed, beginning with obtaining the most current available virologic and surveillance data on which to base strain recommendations issued by the WHO approximately 6 months prior to flu season. While there has been relatively good vaccine matching with predominant circulating strains, some difficulty has been encountered in determining precise antigenic match. New methods are being developed by the WHO and CDC for antigenic matching between circulating and vaccine strains.

Ultimately, many factors influence influenza vaccine effectiveness: recipient age and immune status; vaccine match with circulating strains, quantification of herd immunity, basis of outcome measurement, all contributing to impede measurement of program impacts.

Vaccine recommendations in Canada:

(Drs. Theresa Tam and Pamela Orr)

NACI recommends that immunization programs focus on those at high risk of influenza-related complications, those capable of transmitting influenza to individuals at high risk of complications, and those who provide essential community services to reduce the morbidity and mortality associated with influenza and the impact of illness in our communities. Also recommended for immunization are people in direct contact with poultry infected with avian influenza during culling operations. Further, healthy persons ages 2 to 64 years are encouraged to receive influenza vaccine⁽⁷⁾.

The controversy surrounding the recommendation to immunize healthy pregnant women was discussed. CDC recommends that pregnant women in their 2^nd or 3^rd trimester be immunized, due to the high risk of hospitalization, and considers immunization during any trimester safe. However, further Canadian research is proposed on the need for and safety of influenza vaccines during pregnancy.

In addition to the NACI recommendations, at the 1993 National Influenza Consensus Conference it was determined that "the goal of the influenza immunization program should be 100% coverage of vaccine-eligible groups to prevent serious morbidity and mortality due to influenza in both inter-pandemic and pandemic periods"(8). Specific immunization coverage targets were established as follows: 95% of residents of long-term care facilities and staff by the 1995-1996 season; 70% of persons ≥ 65 years by 2000-2001; and 70% of persons with high-risk conditions by 2000-2001.

Building on the targets established in 1993, additional coverage recommendations were put forward at a 2001 meeting on the role of vaccines in influenza control. Among these were immunization of 80% of persons ≥ 65 years, 80% of health care workers, and 100% of vaccinators by 2003; and 80% of household contacts of high-risk persons by 2005. There were no previous recommendations on national influenza disease reduction targets.

Immunization in Canada:

(Dr. Theresa Tam)

The results of a recent PHAC survey of provincial/territorial immunization programs relative to NACI recommendations for influenza were reviewed. Twelve of 13 jurisdictions have publicly funded influenza programs targeting seniors ≥ 65 years, long-term care facility residents and high-risk individuals 2 to 64 years of age. Only Ontario has a totally universal program (Yukon has a "universal program" for persons ≥ 18 year of age). As of 2004-2005, 12 jurisdictions will have programs for children 6 to 23 months; 10 jurisdictions have programs for health care workers in contact with high-risk people, while seven have programs for household contacts of high-risk people and for essential services. Canada distributes about 10 to 12 million doses of influenza vaccine per year through the public and private sectors.

The most recent national immunization coverage survey (NICS) for selected adult immunizations, conducted in 2001, showed that Canada was close to achieving the identified immunization target for seniors but below the targets for people with chronic medical conditions and those age 18 to 64 years. Coverage was about 68% for persons ≥ 65 years of age, 50% for health care workers and 38% for persons 18 to 64 years of age with chronic medical conditions. While rates varied, provincial/territorial data showed higher coverage for staff (65% to 83%) and residents of long-term care facilities (83% to 95%).

Research and program evaluation:

(Dr. Danuta Skowronski)

Influenza is an important disease that places a burden on Canadian society. It affects 10% to 20% of the Canadian population each year, with 90% of mortality occurring in the elderly, and comparable rates of hospitalization in infants and the elderly. Social costs range from $500 million to $2 billion annually, compared with annual immunization program costs of over $100 million. A national universal program would cost $200 to $500 million per year.

Investment in influenza research and program evaluation is essential to identify current challenges and successful initiatives. Economic analysis is needed to inform changes to publicly funded influenza immunization programs and programs should be evaluated to measure the direct and indirect benefits to society, including the cost effectiveness of vaccinating proposed target groups relative to stated goals. The demand for these studies becomes more urgent as influenza vaccine is recommended to growing segments of the population. Unfortunately, there is currently no routine, annual public spending on program evaluation, a gap the Initiative for Directed Influenza Evaluation and Management (iDIEM) aims to fill. iDIEM is a proposal promoting the strategic design and evaluation of publicly funded influenza prevention and control programs through the ongoing review and effective integration of current evidence covering the spectrum of applied public health research.

The following questions related to setting targets, measuring outcomes and informing program decisions-makers involved with influenza immunization were presented to the audience before moving into working group:

• How much uncertainty about vaccine effectiveness is tolerable when expanding programs beyond persons at high risk of serious sequelae? Do we need a better sense of the relative benefit from year to year? Can this be assessed efficiently?
• How should cost effectiveness be captured in decision-making involving publicly funded programs, and which perspectives should be considered (e.g., third party payer or societal; individual clinician or population-based)?
• Is it practical to set disease reduction targets for influenza?
• What would be appropriate targets for immunization coverage; for specific groups?
• What is needed to measure the impact of influenza immunization programs?
• What mechanisms or strategies are needed to achieve established goals?

It was concluded that influenza is a vaccine-preventable disease that poses unique challenges. It is a moving target, given year-to-year variation in circulating strains, virulence, disease activity and impact, underscoring the importance of ongoing research and program evaluation. To this end, a centrally coordinated and funded Institute similar to the IDIEM was proposed. Participants were also asked to develop a recommendation on the evaluation of existing and proposed influenza programs.

Setting goals and recommendations

Participants recommended the following updated goals and recommendations related to influenza immunization. The discussion guide used by participants is attached in Appendix B.

Goal

The goal of the annual influenza immunization program is to prevent serious illness caused by influenza and its complications, including death.

Discussion: Participants proposed wording changes to the goal set at the 1993 National Influenza Consensus Conference. Rather than "morbidity and mortality" it was agreed the goal should refer to "complications of influenza, including death". Further, rather than "inter-pandemic and pandemic periods," reference should be made to the "annual" influenza program. Consideration was given to identifying "high risk groups", however participants agreed this reference was implicit in the goal and suggested specific populations be addressed as part of a separate recommendation.

Disease incidence

Recommendation 1

National disease reduction goals should be established for influenza.

Discussion: Participants did not recommend disease reduction targets at this time, on the basis that they are difficult to achieve and measure. Specific issues include variability of the influenza virus from year to year, variability in vaccine match to circulating strains, variability in vaccine effectiveness, a lack of disease impact indicators, and limited ongoing research and evaluation.

However, participants did agree that, in conjunction with the establishment of influenza immunization coverage targets and inroads in research and evaluation, disease reduction targets should be established although a timeline was not set for this.

Statement

Herd immunity at the community level is not recognized to be a feasible goal at this time.

Discussion: Participants prepared a statement suggesting, that outside of confined settings, herd immunity is not attainable in Canada at this time. Reasons cited included variability in vaccine effectiveness and practical limitations in achieving necessary coverage levels. It was acknowledged that, in lieu of striving for herd immunity, immunization programs must focus on high-risk groups. Concern was expressed that a limiting statement on herd immunity may negatively impact provinces/territories which have already introduced or are planning to introduce a universal influenza immunization program. However, no changes were made to the proposed statement.

Immunization coverage

Recommendation 2

The following 2001 national immunization coverage targets should be maintained until a task group has been convened and made updated recommendations:

• 95% coverage of residents of longterm care facilities and staff who have extensive contact with residents
• 80% coverage of persons aged ≥ 65 years of age
• 80% coverage of persons < 65 years of age with high risk conditions
• 80% coverage of health care workers
• 100% coverage of vaccinators
• 80% coverage of household contacts of people at high risk

Discussion: Participants devoted substantial discussion to the establishment of immunization coverage targets, ultimately agreeing to maintain the targets set at the 2001 meeting on the role of vaccines in influenza control. It was further agreed that a task group should be established to address gaps and make recommendations related to immunization coverage and program implementation.

Factors contributing to participant concerns about target-setting included the current lack of scientific data upon which to base targets, an inability to quantify the changing target's "denominator" (i.e. the number of persons with high-risk conditions), difficulties defining target groups, and measurement challenges. Further, the design and delivery of vaccine programs varies among provinces and territories, prompting some participants to suggest that provincial/territorial targets may be more appropriate than national targets.

In supporting the maintenance and updating of existing coverage targets, participants cited the critical role of targets in enabling program planning, delivery and evaluation. While the year-to-year variation in influenza incidence and outcomes makes target-setting a challenge, participants agreed that dispensing with targets was not an option.

In arriving at the proposed recommendations, participants agreed that immunization coverage should be maximized for high-risk persons, household contacts of high risk persons, and health service providers. Some concern was expressed about the potential size of the household contacts group, as well as the lack of evidence regarding the effectiveness of this prevention strategy. Ultimately, the following coverage options were considered: 100% of vaccinators; 95% of residents and staff of long-term care facilities; and 80% of persons ≥ 65 years of age. While a priority, no targets were proposed for children 6 to 23 months of age and persons with respiratory and cardiovascular disease.

Other

Recommendation 3

Governments should work collaboratively to ensure that a safe and immunogenic vaccine is available for annual influenza immunization programs.

Discussion: A mechanism is needed to ensure the safety of influenza vaccines, given their unique nature (i.e. a new vaccine is produced yearly under tight time frames based on best available evidence). The suggestion was made to evaluate vaccine safety and immunogenicity annually, with safety defined as a lack of serious adverse effects.

Recommendation 4

Governments should work collaboratively to efficiently deliver influenza immunization to eligible persons each year.

Discussion: Participants agreed on the need to minimize the burden on the health care system posed by influenza. Immunogenicity, based on antibody measurement, may not be an accurate reflection of protection as it does not capture the boost to cell-mediated immunity provided by the vaccine. Rather, the establishment of systems for the annual assessment of vaccine efficacy would be preferable. Such systems could also be used during a pandemic.

Recommendation 5

Governments should work collaboratively to establish a mechanism for strategic design of influenza immunization programs, including applied public health research and program evaluation of:

• basic science
• surveillance
• evaluation of interventions
• knowledge, attitudes and behaviours
• mathematical and economic modeling

Discussion: Participants recommended the establishment of a mechanism for ongoing influenza research and program evaluation to optimize program efficiency and impact.

Vote

Participants agreed to the following goals and recommendations for influenza control, with the lowest level of support given to the recommendation on disease reduction targets. In addition, participants issued a statement indicating that "herd immunity at the community level is not recognized to be a feasible goal at this time".