The federal government will step up its search for possible adverse reactions to the pandemic influenza A(H1N1) vaccine, particularly looking for any cases of Guillain-Barré syndrome, Bell's palsy, and thrombocytopenia that might be linked to the vaccine, according to a report issued by the Department of Health and Human Services.
The National Vaccine Information Center recommended the expanded safety monitoring because 3 of the nation's 13 vaccine safety monitoring systems have picked up weak signals of a possible interaction between the pandemic flu shot and the disorders. The decision came after a meeting of the H1N1 Vaccine Safety Risk Assessment Working Group (VSRAWG). As of March 31, almost 127 million doses of H1N1 pandemic flu vaccine have been distributed in the United States.
The Vaccine Safety Datalink program is the largest of the three systems that found a possible disease link; it contains information on 1.5 million pandemic flu immunizations. This system picked up a weak signal for an association with Bell's palsy.
The Defense Medical Surveillance System, with information on 1.3 million pandemic flu immunizations, and the Veterans Affairs signal detection database, with almost 300,000 vaccination records, both showed a weak signal for thrombocytopenia and idiopathic thrombocytopenia purpura (ITP).
The Indian Health Service, with information on 2.2 million immunizations, showed a weak signal for both Bell's palsy and the blood disorders.
In systems that linked the vaccine and thrombocytopenia/ITP, “the cases are being reviewed to see if the diagnoses are evaluated,” the report noted. “More rigorous comparisons between cohorts with H1N1 vaccine exposure and other vaccines or no exposures are planned.”
The Guillain-Barre Syndrome enhanced surveillance database observed a “potential signal” for that disorder. The database monitors a population of 45 million, but no information was available on how many pandemic flu vaccinations had been examined to determine the possible link. Five other systems are also exploring a possible GBS/pandemic flu vaccine link, the report noted. “Although some systems are reporting elevated relative risks, none have crossed the threshold for a signal. Of importance is the fact that, even if an association between H1N1 vaccine exposure and GBS were substantiated, the estimate is that the vaccine would account for only one extra case of GBS per 1 million persons vaccinated, based on currently available data.”
The nation's primary—and largest—system, however, has picked up no worrisome safety signals. The Vaccine Adverse Event Reporting System (VAERS) has captured information on more than 126 million pandemic flu vaccinations. It found that adverse events after the shots were no different than those occurring after seasonal flu vaccine.
Additional study is needed to determine whether the reported links represent a causal relationship, the report said.