Swine flu myth: The vaccine isn't safe - it has been rushed through tests and the last time there was a swine flu scare the vaccine hurt people. Why take the risk to prevent mild flu?
来源：未知 作者：伊葺解 时间：2019-03-01 09:04:00
By Debora MacKenzie 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. 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 deadly 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. 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. That is reassuring, if true. If the problem in 1976 was contamination rather than some property of the virus, there is no reason to expect a repeat. There has never been a similar problem with any other vaccine. And almost all the pandemic vaccines now being given in the US, the UK 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. The exception is Celvapan. It contains the whole, killed pandemic virus, not a vaccine virus with pandemic proteins, and the virus is grown in cells rather than eggs – making it safe for people with egg allergy. While it and a similar bird flu vaccine have undergone safety testing, no seasonal flu vaccine has yet been made this way. 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. All the pandemic vaccines have had their own safety tests, and almost all are based on seasonal flu vaccines used for years. But very rare side effects can only be detected when millions take them. The seasonal flu vaccines with adjuvants have mostly been given to older people, so we cannot yet be sure that these vaccines do not have very rare side effects in younger people. Celvapan has had no large-scale monitoring. But here are some odds we do know about to consider. 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? Read more: Swine flu: Eight myths that could endanger your life More on these topics: