During past pandemics, a third or more of the entire population has got flu, and the risks of flu killing you or causing nasty problems such as Guillain-Barré syndrome are far greater than those of the vaccines.
Fears from the 1970s
The 1976 vaccine caused around 10 cases per million vaccinated. Even ordinary flu vaccines, however, are thought to cause one extra case of Guillain-Barré per million, in addition to the 10 to 20 per million who get Guillain-Barré some other way every year.
Does this mean it is safer not getting vaccinated? Absolutely not. First, there is the risk of swine flu killing you. Second, what few people know is that flu itself is far more likely to cause Guillain-Barré than any flu vaccine.
A 2009 study found that out of every million people who get flu, between 40 and 70 develop Guillain-Barré. So your best chance of avoiding Guillain-Barré is to get vaccinated, a conclusion backed by a 2007 study.
The vaccine risk is also diminishing. Cases of Guillain-Barré in the US have fallen 20 per cent since 1996, and cases reported after flu vaccination have fallen by 60 per cent. Intriguingly, this coincides with a fall in infections by the food poisoning bacterium Campylobacter, thanks to improved meat hygiene. Guillain-Barré usually follows infections, and Campylobacter is the main cause. It is also endemic among chickens, and flu vaccines are grown in chicken eggs. So the occasional contamination of flu vaccines with Campylobacter proteins might explain the link with Guillain-Barré, according to a 2004 study.
(From the New Scientist)