Nizar Souayah, MD, of the University of Medicine and Dentistry of New Jersey, in Newark concludes that flu vaccines trigger Guillain-Barré syndrome in a subset of the population. He also noted that prospective trials to identify those at risk could easily be done.But there are currently no plans to conduct such trials.
The 62 cases reported to the Vaccine Adverse Event Reporting System represent a rate of 6.2 cases per 10 million people vaccinated, according to Souayah.
In contrast, 51 cases were reported after seasonal flu vaccination, for a reporting rate of 10.6 cases per 10 million people vaccinated, Souayah told reporters at the annual meeting here of the American Academy of Neurology.
He cautioned that the numbers can't be directly compared, but, taken together, both seem to imply that flu vaccines may trigger the syndrome in a very small proportion of people.
With both vaccines, the majority of cases were reported as having begun within the first two weeks of vaccination, Souayah said before his late-breaking poster presentation, a pattern significantly different from what would be seen if there was no link.
In the case of the H1N1 vaccine, he said, 24 cases occurred in the second week after vaccination and 15 in the third week. For the seasonal flu vaccine, the comparable figures were 14 and 12.
"The likelihood of that distribution by chance is almost impossible," he said.
Observers have been keeping a close watch for cases of Guillain-Barré syndrome in the wake of the mass vaccination campaign against the H1N1 pandemic flu. An earlier pandemic flu campaign, in 1976, was halted in midstream when there was an apparent increase in cases of the syndrome.
To help examine that issue with the latest vaccination campaign, Souayah and colleagues turned to the vaccine events reporting system, as well as reviewing charts of the reported possible cases.
All the data were reviewed by a neurologist certified in neuromuscular diseases to confirm the GBS diagnosis, and the researchers excluded GBS cases that occurred within two days after vaccination.
Souayah cautioned that the data were based on passive surveillance, which is subject to a range of possible errors, including under- and over-reporting.
The finding is "consistent with what we are observing in our other more systematic assessments of vaccine safety," said James Sejvar, MD, an epidemiologist with the CDC who was not involved in the study.
While the risk is small for the population as a whole, it may be high for the "tiny proportion of people" who are likely to suffer from Guillain-Barré in the wake of a vaccination, Souayah said. But there is currently no way to tell which people are at risk.
He said prospective trials to clarify the issue could easily be conducted. "It only takes the will," he said.
While the risk is small for the population as a whole, it may be high for the "tiny proportion of people" who are likely to suffer from Guillain-Barré in the wake of a vaccination, Souayah said. But there is currently no way to tell which people are at risk.
He said prospective trials to clarify the issue could easily be conducted. "It only takes the will," he said.
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