Vaccination Curtails Influenza Outbreaks, but Side Effects are Still Possible

Dr. Allison McGeer MSc, MD FRCPC
Director,
Infectious Control,
Mount Sinai Hospital,
Toronto, ON

Every year, approximately one in six Canadians are infected with influenza. Healthy adults infected with influenza miss, on average, 2-7 days of work, and have a 10-30% chance of being prescribed a course of antibiotics. Influenza causes approximately 20% of all cases of acute otitis media in children,¹ and is the most common single infectious cause of hospital admission in young children.^2-4 However, the greatest impact of influenza is seen in the elderly. Every year, nearly 1% of older adults with any chronic underlying illness require hospital admission due to influenza, and about 4000 die from influenza and its complications.⁵

Vaccination is the only effective method for the prevention of influenza. Annual vaccination is required because influenza viruses are able to mutate their antigenic coat continuously in order to evade the human immune system (see "Chasing Away the Flu Bug" on page 20 for a more detailed description of this process).