As millions of people worldwide begin getting the new swine flu shot, public health officials are bracing for rumors about dangerous side effects linked to the vaccine.
To provide context, experts combed hospital databases and population samples in Britain, Canada, Finland, the United States and elsewhere to find daily baseline rates of commonly reported events like Guillain-Barre syndrome, sudden deaths, seizures and abortions. The research was published online Saturday in the British medical journal Lancet.
They found that in Britain, for every 10 million people who might get the swine flu shot, about 22 cases of Guillain-Barre syndrome and 6 unexplained deaths will likely occur within 6 weeks of vaccination
- and probably won't be caused by the vaccine.
In the U.S., experts expect that for every 1 million pregnant women who get the swine flu shot, 397 will have a spontaneous abortion within a day.
Only if the rates of these events exceed these baseline numbers should experts suspect the vaccine might be responsible.
"People die every day for lots of reasons, but we tend not to think about that when a mass immunization campaign is happening," said Steven Black of Cincinnati Children's Hospital in Ohio, one of the paper's authors. "We're not saying we don't need to look at vaccine safety, but let's do it judiciously."
Black, like several of the study's authors, received grants from companies that make swine flu vaccine.
Mass immunization campaigns for diseases like measles and yellow fever have frequently been undermined by rumors that the vaccines cause dangerous side effects.
Still, rumors may also mask legitimate vaccine concerns. In Nigeria, fears that the oral polio vaccine causes HIV were unfounded but concern about the vaccine was not entirely unwarranted: it does cause polio in rare instances.
