People will die after swine flu vaccine - but it's just coincidence
By Rebecca Smith and Kate Devlin, Medical team
Published: 8:00AM GMT 31 Oct 2009
With millions of people being vaccinated against the virus there is a real risk that coincidental events will be seen as reactions to the jab, a paper in The Lancet said.
Experts at Cincinnati Children's Hospital in America calculated the background rate of conditions that may be mistaken for vaccine reactions and warned that there is a risk people will shun the jab needlessly.
Only if these background rates are exceeded will it point to a potential problem with the vaccine.
Medical experts have been told to watch for any cases of Guillain-Barré syndrome during the flu pandemic as some research suggested there was a link between a flu vaccine used in America in 1976 and the condition, in which the body’s immune system mistakenly attacks part of the nervous system and can be fatal in rare cases.
However flu itself it also linked to the condition and about one in every 100,000 people a year.
Dr Steven Black and colleagues calculated that if 10 million people in Britain were vaccinated there would be around 22 cases of Guillain-Barré syndrome and six cases of sudden death would be expected to occur within six weeks of vaccination as coincident background cases.
Just over nine million people in priority groups, such as pregnant women and those with long-term illnesses, and another two million front line health and social care workers will be offered the vaccine in Britain over the next two months.
Decisions will be taken soon over whether to offer the vaccine more widely.
The research also suggested that 397 per one million vaccinated pregnant women would be predicted to have a spontaneous abortion within one day of vaccination.
But this is the rate of spontaneous abortion that would occur on any given day out of a group of one million pregnant women during a vaccination campaign or not.
Dr Black wrote: “Misinterpretation of adverse health outcomes that are only temporally related to vaccination will not only threaten the success of the pandemic H1N1 influenza vaccine programme, but also potentially hinder the development of newer vaccines.
"Therefore, careful interpretation of vaccine safety signals is crucial to detect real reactions to vaccine and to ensure that temporally related events not caused by vaccination do not unjustly affect public opinion of the vaccine.
"Development and availability of data banks that can provide locally relevant background rates of disease incidence are important to aid assessment of vaccine safety concerns.”
The researchers said although scientists know that events connected only be time does not prove cause and effect, the cases 'nonetheless raise public concern'.
Prof David Spiegelhalter, Winton Professor of the Public Understanding of Risk, University of Cambridge and Co-Director of Straight Statistics, said: "What a fine paper. If millions of people are vaccinated then just by chance we can expect bad things to happen to some of them, whether it's a diagnosis of autism or a miscarriage.
"By being ready with the expected numbers of chance cases, perhaps we can avoid overreaction to sad, but coincidental, events. And why don't we ever see a headline 'Man wins lottery after flu jab'?"
Professor Robert Dingwall, University of Nottingham, said: "The difference between cause and coincidence is difficult enough for specialists to grasp, let alone the wider public.
"However, this paper is very important in spelling out the fact that just because two events happen at the same time, they are not necessarily related. There is a background rate of death, disease and accidents that happen all the time regardless of what medical interventions are going on.
"Confusing cause and coincidence may lead to serious policy mistakes that put people unnecessarily at risk.
"I am sure that some coincidences will emerge from a high-profile vaccination campaign and we must be careful not to be misled by them."
Meanwhile the World Health Organisation said that pregnant women could be immunised with any of the vaccines licensed for use against swine flu.
Dr Marie-Paule Keiny, from the WHO, said: “ Sage (the Strategic Advisory Group of Experts) has concluded that the safety profiles are good and recommend that pregnant women can be immunised with any of the licensed vaccines.”
The WHO also recommended that one dose was sufficient to immunise children.