October 30, 2009

experts react to paper to be published in Lancet on vaccination campaigns

This study looks at the likelihood of adverse events, such as Guillian-Barré Syndrome or sudden death, whether or not people have recently been vaccinated. The authors state that ignoring these figures can cause unnecessary panic.

Dr Punam Mangtani, clinical senior lecturer in epidemiology at the London School of Hygiene and Tropical Medicine, said:

“The review provides a ‘one stop shop’ of very useful, and previously difficult to access, information on background rates of events that occur anyway without vaccination. People and health care staff now have a better idea when they hear of any adverse events that occur at the same time as vaccination of whether it is co-incidence or not. Important events are sad, but can’t be associated with vaccination without investigations that include knowing the size of the population they have occurred in, what other factors existed that may have been the cause of the event, or what the increased likelihood is of the reporting of such events at the moment.”

Prof Adam Finn, Professor of Paediatrics, University of Bristol Medical School, said:

“Vaccines are an easy target. When something bad happens to our children we want to know why. If they have recently had a vaccine, that seems like the obvious explanation. But bad illnesses happen all the time and, if you immunise enough people, chance dictates that some of them will get the injection shortly before a bad illness that was going to happen anyway. Who are the losers? The children who get vaccine-preventable illnesses after missing out on protection because of false fears about safe vaccines.”

Prof 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. This paper should help to minimize that risk for the conditions that we know about – like Guillain Barre. However, we must also be careful not to make hasty links between vaccination and events that are not as well-documented as those summarized in this paper. An example from earlier this summer would be the supposed association between oseltamivir and nightmares – actually nightmares do seem to be associated with fevers more widely but haven’t really been recorded as a symptom until treatments were being offered. So some people with fevers get nightmares but these are not thought to be clinically significant until they coincide with a drug treatment, when they start being recorded as an associated, but not causally linked, event. I am sure that some similar coincidences will emerge from a high-profile vaccination campaign and we must be careful not to be misled by them.”

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 over-reaction to sad, but coincidental, events. And why don’t we ever see a headline ‘Man wins lottery after flu jab’?”