Highlights of the National Advisory Committee on Immunization statement on influenza for the 2006–2007 season

Although international avian influenza may be occupying media headlines and the minds of many Canadians, behind-the-scenes planning by the public health community and health care providers is underway for this year's seasonal visit of influenza. In the National Advisory Committee on Immunization (NACI) annual statement on influenza immunization,1 published June 15, are found a few changes that affect our strategies for prevention in 2006–2007.

NACI has reiterated the importance of vaccine as the primary means to prevent influenza, which is a major cause of ambulatory visits, antimicrobial use, hospitalization and death, particularly among those older than 65. In Canada the national strategy to decrease the burden of illness attributable to influenza has been risk-based, rather than universal, immunization. The programs to identify and deliver vaccine to subpopulations at higher risk than healthy people for complications are provincial– territorial. In much of Canada, physicians must identify the individuals in their practices who are at risk, educate them and their families about vaccine, and deliver 1 or 2 doses to each as needed, all within a few months every fall.

The groups recommended to receive influenza vaccine in 2006–2007 have not changed, although a new combined category for those at high risk has been created, inclusive of people in higher-risk age groups (5–23 months or > 65 years) or who have an underlying health condition. Populations that were added last year to the list of recommended recipients (i.e., healthy children aged 6–23 months, their caregivers, and people with conditions that “compromise the management of respiratory secretions and are associated with an increased risk of aspiration”)2 continue to be recognized as being at increased risk of infection.

NACI continues to strongly recommend vaccine for persons who can transmit influenza to high-risk people and has worded this recommendation more inclusively. All household contacts of individuals at high risk should be vaccinated, as should all providers of health or other care in facility or community settings “who, through their activities, are potentially capable of transmitting influenza to vulnerable populations.”

This year's statement emphasizes the importance of immunizing pregnant women who have underlying health conditions and briefly reviews the supporting literature. Although vaccination is encouraged in any trimester of pregnancy, NACI has not taken the step (as has been done in the United States)3 of recommending vaccine for healthy pregnant women (unless they are expected to deliver during flu season, since they then become a contact of the infant).

For the rest of the Canadian population, healthy people aged 2–64 years who are not pregnant and will not be in close contact at home or at work with high-risk people, NACI continues to encourage vaccine. This permissive wording allows physicians to recommend vaccine for all their patients, although at present only Ontario and the Yukon fund such programs. The evidence of influenza vaccine efficacy is strongest in healthy people, among whom cases are reduced by up to 70%.4 In the universal influenza immunization program in Ontario, increasing influenza vaccine coverage of those aged ≥ 12 years has been associated with higher coverage for people with high-risk chronic conditions than has occurred in other provinces.5 This suggests that universal immunization may increase vaccine delivery to high-risk groups. The merits of a universal approach to influenza vaccination were discussed recently at the US Advisory Committee on Immunization Practices (ACIP), along with a proposal to work toward immunizing all school-aged children by 2008– 2009 and universal immunization of Americans by 2012–2013. This year, ACIP voted to expand immunization of young children to include those aged up to 58 months.3 Since immunization of people 50 years or older is already recommended, this can be seen as an incremental step toward universal immunization.

The other notable recommendation that will affect planning for the coming season is NACI's advice to use only neuraminidase inhibitors for antiviral prophylaxis. This recommendation was made in the midst of last year's influenza season, when antiviral susceptibility testing revealed that 82% of isolates were resistant to amantadine, and that these drug-resistant viruses were present across Canada.6 The advice to use only neuraminidase inhibitors will most affect physicians who work in institutions where outbreaks occur (including residential settings) or who provide care to high-risk people who cannot be given vaccine or are immunocompromised. It is unclear whether amantadine will have a role in the treatment or prevention of influenza in seasons to come.