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Background: In response to the 2009 H1N1 pandemic both British Columbia and Washington State implemented campaigns to deliver monovalent influenza vaccine to their citizens. Most vaccine used in British Columbia was a novel squalene adjuvanted inactivated vaccine whereas the inactivated vaccine (MIV) administered in Washington was unadjuvanted and based on ‘seasonal’ formulation vaccine.
Setting: British Columbia and Washington State had comparable passive systems in place to monitor reports of AEFIs. Both jurisdictions tracked the number of doses of vaccine administered. Rates of AEFI reporting following receipt of inactivated vaccine were compared overall, and by severity of event.
Population: The population demographics of these jurisdictions are similar and lend themselves well to comparison of adverse events following immunization (AEFIs).
Project Description: Approximately 1.59 million doses of adjuvanted vaccine were administered in British Columbia, and reports of AEFIs for 381 individuals were received. The rate of AEFI reporting was 24.0 per 100,000 doses administered overall with 1.5 serious adverse events reported per 100,000 doses. 93.7% of AEFI reports in the province were not serious. An estimated 990,000 doses of MIV were distributed in Washington State. Adverse events were reported for 134 individuals following receipt of MIV, for an overall rate of 13.53 AEFIs reported per 100,000 doses of MIV administered with 1.21 serious adverse events reported per 100,000 doses. 91% of AEFI reports in the state following receipt of MIV were not serious.
Results/Lessons Learned: Distribution of inactivated H1N1 vaccine to demographically similar populations in neighboring jurisdictions yielded comparable rates of serious AEFI reporting in British Columbia and Washington State, despite the use of vaccines with significantly different formulations.