Influenza vaccines are continuously modified to adjust to the virus antigenic shifts or drifts, and its safety profile may vary. While generally considered safe, influenza vaccines have been associated in the past with increases in cases of Guillain-Barré syndrome (1976) and with oculorespiratory syndrome in 2001. Last year, with the vaccination against the pH1N1, an increase of allergic-like reactions was observed.

Passive surveillance is collecting notifications of adverse events (AE) on the whole population but the sensitivity of this system is not high and its timeliness is not necessarily optimal. Last year, with the new pandemic Influenza vaccine the investigators piloted a web-based active surveillance of a large number of health care workers (HCW) vaccinated with the new adjuvanted monovalent pH1N1 influenza vaccine (Arepanrix® GSK, Canada). Because healthcare workers (HCW) constituted a well-defined group with general good health and received the Influenza vaccine in priority, this group of people was well suited for monitoring the safety of the influenza vaccine. For this study, 6242 HCW were recruited in three different sites (5183 were from Quebec). A total of 468 events (local reactions, fever, systemic reactions, gastrointestinal and respiratory problems) were reported by 430 HCW. 80% of the HCW recruited completed at least one of the three surveys and 52% responded to all questionnaires. During this surveillance, the investigators didn't have unexpected findings but this active surveillance of adverse events among healthcare workers would have been effective enough to rapidly detect adverse events occurring at a rate ≥ 1 per 200 vaccinees. For this year the investigators want to expand the surveillance to more sites and more participants to be able to detect AE occurring at rates ≥ 1 per 500 vaccinees, and to increase the response rate to all three surveys in participants.

The main objective of this project is to estimate in HCW vaccinated against influenza the frequency of adverse events of sufficient severity to cause work absenteeism or medical consultation.

This year the network will include 5 Canadian hospitals (Quebec City, Vancouver, Toronto, Halifax, + another one ) with a total enrollment of >10 000 HCW. This should allow us to detect AE occurring at a rate of ≥ 1 per 500 vaccinees.

Inclusion Criteria:

• To be a healthcare worker from one of the seven Canadian Hospitals participating in the Public Health Agency of Canada/Canadian Institutes for Health Research-Influenza Research Network (PCIRN): Quebec City, Toronto, Halifax, Vancouver, Ottawa and Sherbrooke.
• To have been immunized with the influenza vaccine 2010
• To have an email address
• To be 18 years old and older
• To have sign the consent form

Exclusion Criteria:

• Pregnant women

The active surveillance was conducted in five Canadian hospitals participating in the Public Health Agency of Canada/Canadian Institutes for Health Research-Influenza Research Network (PCIRN): Quebec City, Toronto, Halifax, Vancouver (2 sites), Ottawa and Sherbrooke. Healthcare workers immunized in these institutions were offered to participate in a web-based active surveillance of vaccine safety.

Only 70% answered the 2 surveys. We don't know why 30% didn't complete the 2 surveys (were they too sick or not motivated).We didn't have a group of comparable unvaccinated individuals (to estimate the risks attributable to the vaccine).