Monitoring adverse events of the vaccination campaign against influenza A (H1N1) in the Netherlands.

BACKGROUND

In November 2009, a vaccination campaign against Influenza A (H1N1) was started in the Netherlands. The accelerated registration procedure of the vaccines used in this campaign and the use of these vaccines on a large scale indicated a need for real-time safety monitoring.

OBJECTIVE

To describe the processing, analysing and performing of signal detection by the Netherlands Pharmacovigilance Centre (Lareb) on reports of adverse events following immunization (AEFI) with respect to the two pandemic influenza vaccines, Focetria® and Pandemrix®, used in the Netherlands. The secondary aim is to provide a summary of the results of the safety monitoring of both vaccines.

STUDY DESIGN

Description of the process of collecting information and analysis of the safety monitoring of the pandemic vaccines during the vaccination campaign against H1N1 in the Netherlands. An observational study on adverse events following immunization (AEFIs) associated with vaccines used in this campaign was conducted.

RESULTS

The use of a dedicated web form with predefined AEFIs enabled an efficient way of processing and analysing the reports, resulting in a close to real-time monitoring of the safety of the vaccines. From 1 November 2009 until 1 March 2010, 7534 reports concerning one or more AEFIs possibly related to the administration of both vaccines were received. 2788 of the reports related to Focetria® and 4746 of the reports related to Pandemrix®. The total time between receiving the reports and completion was longer for the serious reports (average 2.8 days) compared with the non-serious reports (average 0.8 days). The profile of the reported adverse events is comparable with the information provided in the Summary of Product Characteristics (SPC). Differences in reported AEFIs between both vaccines may be caused by bias and confounding due to the different populations for which these vaccines have been used. No signals of possible batch-related problems were detected for either vaccine.

CONCLUSIONS

The method applied allowed for real-time monitoring for AEFIs during the mass vaccination campaign. The use of web-based forms, preferably with information on venue and used batch numbers, enabled an efficient monitoring of possible batch-related problems. No major safety issues occurred with respect to the type of reported AEFIs, or with the batches of either vaccine.