By: Mark Lemstra
10 November 2010
This is the first in a four-column series on influenza. The first will discuss the ineffectiveness of immunization for the flu in most populations. The second column will discuss the great influenza epidemic of 1918 and the lessons we still have not learned.
The third column will discuss last year’s H1N1 embarrassment and the fourth one will put everything together, with recommendations for prevention and management.
In 1918, out of a total world population of 1.8 billion, 50 million people died from influenza or from complications associated with influenza. In that unusual period of time, a majority of the population was susceptible to infection.
However, the specific reasons for the high infection rate and subsequent deaths are rarely, if ever, discussed. To face a similar threat today, the conditions present in 1918 would have to be replicated. That is not likely.
All of that said, influenza is no joke, because it is a factor in the deaths of approximately 4,000 Canadians every year, most of whom are already very sick and elderly. So let’s start with flu immunizations for the elderly.
A research team recently reviewed every published paper on the effectiveness of vaccines in preventing influenza in the population aged 65 or older. There were 75 such papers published from 1966 to 2009. Regrettably, only five involved high-quality randomized trials, while the others were low-quality observational studies, with significant amounts of bias built into their designs.
The findings were published in the highly regarded Cochrane Collaboration series of systematic literature reviews.
The review authors concluded: “The available evidence is of poor quality and provides no guidance regarding the safety, efficacy or effectiveness of influenza vaccines for people aged 65 years or older.”
One of their more interesting conclusions said there was “no association between vaccine coverage and attack rate.”
For example, a study published in 2002 involved the immunization of 98 per cent of the elderly population, with an observed illness rate of 40 per cent. In comparison, a study published in 1985 immunized 27 per cent of the elderly population, but only 17 per cent of the population became infected. In other words, factors other than immunization protect the population from influenza.
So, what is the problem with research on flu immunizations for the elderly? It is perhaps ironic that the authors found that “those with terminal illness or with socio-economic disadvantages are less likely to be vaccinated,” and as such “this fact enhances vaccine efficacy.”
Coupled with this is the reality that healthy seniors are the ones most likely to request immunization for the flu.
Thus, the observational studies have inflated the potential effectiveness of the flu vaccine for seniors in the real world.
Read the entire story here.