All of which begs the obvious question – how effective are they? Different studies are hard to compare because they measure different outcomes. Some look at rates of hospitalisation, others at death rates or at the number of laboratory-confirmed flu infections. But to take an example, a large study from 2007 published in the highly regarded journal, The New England Journal of Medicine found the vaccine protected seven out of ten people. Protection also varies from year to year, depending on the accuracy of the WHO’s predictions. Preliminary data from the US Centers for Disease Control estimate that the 2010/2011 flu vaccine was approximately 60% effective.
That said, some people respond to the vaccine better than others, and this can depend on age. Protection is lower for those over 65, but the consequences of contracting flu can be more severe, which is why older people are targeted for vaccination. If people get flu despite having the vaccine, it’s not that vaccine gave them flu that winter, but that it didn’t protect them against it. And if you do get flu despite having had the vaccine, the chances are it would have been more severe without it.
Then there is another possibility, which is that you have a cold. And as horrible as it might feel, this is not the same as flu. There is a tendency to describe a bad cold as flu in order to convey to people quite how ill you are. I’ve done it myself. But the first time I had real flu I realised the difference. When I was recovering I made the mistake of going to rent a DVD from a shop five minutes walk away. The whole trip proved so exhausting that I had to sit on a bench for an hour to muster the energy to get back home. Colds and flu can both can involve sneezing, coughing and aching muscles, but flu usually comes on much more quickly, often starting with a sudden fever.
Yet despite the evidence available, many people remain convinced that vaccines can cause flu. In a study conducted by health psychologist Lynne Myers last year – not on the seasonal flu vaccine, but on the swine flu vaccine – only 53% of people surveyed correctly answered that the vaccine can’t cause swine flu. The evidence may be in favour of the vaccines, but the problem is that when we experience symptoms ourselves we make assumptions based on our own ideas about causality. It’s very hard not to connect events when the timing seems to fit. But that doesn’t always mean we’re right.
You can hear more Medical Myths on Health Check on the BBC World Service.
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