The Therapeutic Goods Administration has published the results of investigations into a spike in fevers and convulsions associated with seasonal influenza vaccination of young children. The report details a range of investigations that have been undertaken.
Of 123 reports of febrile convulsions in children under 5 received by June 4, the TGA says 100 cases have been confirmed nationally, 58 of which were reported from WA.
Of the 100 cases, 99 are considered causally related to vaccination with seasonal influenza vaccine and 1 case is considered unrelated because of the lack of a temporal association with vaccine administration. Of the 99 cases considered causally related, 74 are considered very likely to be related to influenza vaccination because no other potential causative factors have been identified. The remaining 25 cases are only possibly causally related to the vaccine because they could also be explained by the concomitant administration of one or more other vaccines and/or a concurrent infection.
The CSL products FLUVAX or FLUVAX JUNIOR were used in all 66 cases where the brand of the seasonal influenza vaccine was reported. While the TGA says the evidence “most clearly points” to an increased risk with FLUVAX, “there is currently no evidence of a similar safety signal from the other seasonal influenza vaccines INFLUVAC and VAXIGRIP, although numbers of administered doses of these vaccines at this time are too small to be certain that the matter is confined to the FLUVAX vaccine”.
The TGA says there are no apparent clinical or epidemiologic factors that would point to a plausible explanation for the observed rates of fever and febrile convulsion. It also says that: “At this stage, based on findings from the two TGA audits and information from the US FDA audit, it has not been possible to identify a manufacturing deficiency that is causally linked to the occurrence of a higher than expected rate of febrile convulsions.”
The TGA’s messages aren’t crystal clear, however. On one hand, it concludes that “while epidemiological analyses to date demonstrate an excess of fever and febrile convulsions in children 6 months to 5 years, the overall risk benefit balance of both products remains positive”.
On the other hand, it says amendments to the Product Information documents for both products have been made:
- under Precautions, notification of an increase in reports of fever and febrile convulsions in young children during the 2010 Southern Hemisphere influenza season, and that the individual risk benefit balance for the use of FLUVAX in children aged less than 5 years should be carefully considered.
- under Post Marketing Adverse Events, references to rates of fever and febrile convulsions reported in 2010.