Less Than 40% of Elderly are Getting Flu Shots
Michele Kohli, BSc, MSc
The persistence of influenza in the North American population has not been completely explained by epidemiologists.1 During the last influenza season (1997-98), there were 5,148 laboratory confirmed cases of influenza in Canada (see Table 1).2 The elderly population, those aged 65 years and above, are particularly susceptible to this disease. Over 95% of the deaths caused by influenza occur in this age group, in part, because of the higher prevalence of congestive heart failure and lung disease.1 Last year, the occurrence of influenza peaked between January and March.2 When the prevalence of influenza is high in a population, patients presenting with a febrile respiratory illness along with symptoms such as myalgia, headache, sore throat and cough are often diagnosed as having influenza.1 However, the gold standard for diagnosis is laboratory detection of the virus in nasopharyngeal swabs.1 The genes of the influenza virus mutate frequently, causing the antigenic molecules of the virus to change, resulting in the emergence of new viral sub-types. This process is known as antigenic drift. When human and swine or avian strains of influenza A recombine, the resulting new subtypes can cause pandemics.3
The Number of Laboratory Confirmed Cases of Influenza in Canada, from September 1997 to April 1998, by Province.2 Province Number of Cases Newfoundland 85 Nova Scotia 96 PEI 5 New Brunswick 85 Quebec 768 Ontario 2,783 Manitoba 166 Saskatchewan 224 Alberta 560 British Columbia 376
Unfortunately, the volatility of the virus means that people must be vaccinated for influenza annually. The composition of the vaccine changes each year, depending on which strains are predicted to circulate in the population. In Canada, annual vaccination is recommended for several high risk groups including all persons aged 65 years and older, all persons living in long term care facilities and all health care workers who have contact with members of these high risk groups.1,2 These people receive the vaccine free of charge. Dr. Monika Naus, Physician Manager, Disease Control Service and Provincial Epidemiologist for the Ontario Ministry of Health, estimates that 1.85 million doses of vaccine are delivered annually in Ontario, with about 1.32 million of these being given to the elderly. This year in Canada, only split-level vaccines are available. This variety of vaccine has been chemically treated to reduce febrile reactions.2 The efficacy of the influenza vaccine has been estimated at 70 to 80 percent. Studies have shown that vaccination significantly reduces mortality from all respiratory diseases, hospitalization as well as incidence of the disease.3 The vaccine is contraindicated in patients with allergies to eggs and should not be given to patients with a febrile illness until they have recovered.
The occurrence of other respiratory diseases, such as