Published: March 2011
Publications
Seasonal flu vaccine - an update on spontaneous reporting
Prescriber Update 32(1): 4
March 2011
Overview
CARM and Medsafe thank everyone who contributed to the reporting of adverse events to the seasonal flu vaccine last season.
In total, at the end of the season (31 July 2010), CARM had received 396 reports detailing 936 events. This compares with 135 reports submitted in 2009.
Although the reason for the change in reporting pattern is difficult to fully elucidate, the increase in reports is thought to be due to extending the eligibility criteria for funded vaccine (hence more people vaccinated) and stimulated reporting due to publicity of adverse events in Australia.
In 2010 three seasonal influenza vaccines were funded by the Ministry of Health: Infl uvac, Fluvax and Vaxigrip. Over 1 million doses of vaccine were distributed: 275,000 doses of Infl uvac; 265,000 doses of Fluvax; with the remainder being Vaxigrip.
The distribution of suspected adverse reaction reports per brand of vaccine was: 197 for Fluvax, 119 for Vaxigrip, 52 for Influvac and 28 brand unknown. In children under 9 years of age the majority of reports involved the Fluvax brand while in adults and children over 9 years of age there was an even distribution of reports received for Fluvax and Vaxigrip.
Reported suspected reactions
The most commonly reported suspected reactions following immunisation were:
- fever (131 reports),
- vomiting (86 reports),
- injection site inflammation (51 reports) and
- headache (48 reports) .
There are also reports of rare neurological or immunological conditions that occurred in temporal association with immunisation with seasonal flu vaccines. However their causal association cannot be confirmed and may refl ect coincidence.
Last season CARM received two reports of convulsions (one in a known epileptic) and one report of transverse myelitis (in a patient with alternative causal factors). There was also one report of a sudden death (considered unrelated to immunisation by the coroner).
Febrile reactions
On 22 April 2010 the cessation of the influenza vaccination programme in children was announced in Australia. This action was taken due to the high number of reports of febrile convulsion in children in Western Australia immunised with seasonal flu vaccine. At that time, in NZ, CARM had received four reports of febrile convulsions; three in association with Fluvax and one brand unknown.
An advisory was issued by the Ministry of Health not to use Fluvax in children, but to continue vaccinating children using other brands. Subsequent to this CARM received a further six reports of febrile convulsions in children. These reports detailed events that had occurred before 22 April 2010 and possibly reflect stimulated reporting.
In summary, of the 10 cases of febrile convulsion: seven were associated with Fluvax, one with Influvac and two were unknown brand. Five of the 10 children who experienced a febrile convulsion had a history of febrile convulsion to previous immunisations.
A crude estimate of the reporting rate of febrile convulsions in New Zealand, in association with Fluvax, did not indicate that the reporting rate of febrile convulsion was above the expected rate for seasonal influenza vaccines of 1 case per 1000 doses. This estimate used preliminary numbers of children under five years of age given funded vaccine.
The 131 reports of fever included 106 reports in children. The majority of reports (81%) were associated with Fluvax. In most cases (89%) the onset of fever was reported to have occurred within 24 hours. However as the temperature was not reported in most cases the presence of fever or the severity cannot be confirmed.
Conclusions
After analysis of the reports received in New Zealand, CARM considered that although there was an increase in reports the nature of the reports was as expected for vaccine adverse events. The reports of febrile convulsions were in line with expected reports for administration of vaccines in children.
Next Season
In response to the events in Australia in 2010 the manufacturer of Fluvax is investigating the root cause of the increase in febrile reactions.
As a precautionary measure for the 2011 season, pending the results of these investigations, Fluvax will only be indicated in adults and in children aged five years and above.
Two brands of the seasonal flu vaccine will be funded in 2011: Fluvax (Adobe PDF document 101 KB) and Fluarix (Adobe PDF document 50 KB).
