21 October 2009
The UK starts vaccinating people against swine flu today; in the US and Australia, vaccination has already begun. Can we be sure that safety hasn't been compromised in the race to test and produce the vaccine? Didn't vaccination hurt people during the last big swine flu scare? And do the benefits of vaccination outweigh the risks? In this excerpt from our in-depth feature Swine flu: fact versus fantasy – to be published in full next week – New Scientist sorts the myths from reality.
This flu isn't always mild and unlike ordinary flu it mostly kills young people, including the healthy (see diagram). You might be one of the unlucky few. And even if you only get the mild version yourself, you might infect a family member or friend who then becomes severely ill. So doing nothing is risky, even if the odds are low.
What about the vaccines? People's nervousness about swine flu vaccines is understandable. In 1976, after the death of a US army recruit triggered fears of a repeat of the 1918 pandemic, around 48 million Americans were given a swine flu vaccine. Of these, 532 developed Guillain-Barré syndrome, a paralytic condition caused by rogue antibodies attacking nerve cells. Most people recover from Guillain-Barré, but not all; 25 died after 1976 and others suffered lasting damage.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.The new vaccines
That is reassuring, because if the Guillain-Barré after the 1976 swine flu vaccine was indeed due to Campylobacter contamination, there is no reason to expect a repeat this time round. The pandemic vaccines now being given in the US and Australia are being made in the same plants and in the same way as ordinary flu vaccines. Only two proteins on the vaccine virus have been changed, to match the 2009 H1N1 virus, and these proteins are similar to those of seasonal H1N1 flu, which have been in vaccines since 1977.
Another potential worry are the immune-stimulating chemicals called adjuvants that are added to some vaccines. The World Health Organization asked countries to make pandemic vaccines with adjuvants because much less of the key ingredient, dead flu virus, is needed per dose – meaning far more doses can be produced. The US could not do this because no seasonal flu vaccines with adjuvants had already been tested and approved there. In Europe they have been, so the main pandemic vaccines being given in Europe – Pandemrix (PDF) and Focetria – do contain adjuvants. The exception is Celvapan, which is grown in cells rather than eggs – meaning no risk of Campylobacter contamination – and does not contain an adjuvant.
Seasonal flu vaccines with adjuvants have undergone a full battery of safety tests in previous years. But very rare side effects can only be found by watching for them after the vaccine is on the market and given to thousands of people. Adjuvanted vaccines for ordinary flu have mostly been given to older people, so that is where most surveillance has taken place. We do not know for sure if these vaccines have very rare side effects in younger people. But here are some odds we do know about to consider.The odds
The risk of getting Guillain-Barré from a flu vaccine is almost certainly less than 1 in a million; the risk of getting it from flu itself is more than 40 in a million. Swine flu is estimated to have killed 800 people in the US already, or more than 2 in every million so far. And during the first wave of swine flu this summer, 1 out of every 20,000 children aged 4 or under in the US ended up in hospital.
Still think it's safer not to get vaccinated?
