BACKGROUND:
During the 2000-01 influenza season Health Canada received unusual reports of ocular and respiratory signs and symptoms following influenza vaccination. The syndrome, labelled "oculorespiratory" (ORS), was linked mainly to one of three vaccine products distributed. Investigation revealed a physicochemical difference between vaccines, but in subsequent seasons after this was resolved, ORS was still found to be associated with all influenza vaccines.

OBJECTIVE:
To review the experience with ORS in Canada over several influenza seasons in order to assess its significance as a new influenza vaccine-associated adverse event (VAE).

METHOD:
Influenza VAE case reports to the passive surveillance system from 1999 - "pre-ORS" - to 2003, were analysed for events meeting the case definition of ORS.

RESULT:
The reporting rate of all VAEs prior to the ORS season was estimated at 76 per million doses, and rose dramatically to 246, 213, and 119 in subsequent seasons (2000-01 to 2002-03 respectively). VAEs meeting the ORS case definition were found prior to 2000 at 4/million, but rose to 124, 103, and 50 respectively. The majority of ORS cases were females between 45 to 64 years of age, who generally described the syndrome as mild.

CONCLUSION:
Although more severe and higher numbers of ORS cases were reported in 2000-01, ORS is not a new VAE. ORS has likely always existed though underreported, reflecting its mild nature. The dramatic increase in reporting rates for all influenza VAE likely reflected publicity and encouraged reporting, a trend that is slowly waning. Influenza illness carries much higher morbidity, leading public health authorities to maintain strong recommendations for yearly influenza vaccination.

LEARNING OBJECTIVES:
Recognition of a new syndrome, importance of adverse event surveillance, and balancing of risks and benefits.