Influenza (the flu) is a respiratory infection caused by the influenza A and B viruses. Though influenza is often a mild illness lasting seven to 10 days, adults over 65 are at risk of severe disease and complications. Others at risk of serious disease are young children, pregnant people, and those with chronic medical disorders. Influenza causes 12,200 hospitalizations and 3,500 deaths a year in Canada.

The influenza vaccine is safe and effective. It becomes available in the fall, and you should offer it to your patients before the flu season. Several vaccines are approved for use in Canada. 

Influenza Risk in Older Adults

Influenza commonly presents with fever, chills, runny nose, cough, headaches, and fatigue. Most people recover in less than two weeks, but immunosenescence – or changes in the immune system associated with age – places older people at higher risk for complications. The most frequent complication is pneumonia, caused either by the influenza virus or a secondary infection. Other complications are myocarditis, encephalitis, myositis and rhabdomyolysis, multiple organ dysfunction, and the exacerbation of pre-existing conditions like asthma and chronic heart disease.

People over 65 with influenza can be treated as outpatients but require monitoring for danger signs like dyspnea, confusion, and drowsiness. Seizures and unconsciousness signify hypoxia or brain involvement such as encephalitis. Adverse outcomes of influenza, like hospitalization, intensive care unit admission, and mortality, are more frequent in older people.

• Influenza affects all age groups, but 50 to 70 percent of hospitalizations occur in people over 65.
• Mortality is also higher; 89 percent of deaths are in people over 65.

Influenza Vaccine

The influenza vaccine is formulated every year according to the circulating strains of the virus. The vaccine becomes available in July or August. Canada’s National Advisory Committee on Immunization (NACI) advises that it should be offered as soon as it is available as flu season activity begins as early as October. Influenza vaccine should be given later in the season, too, if it is available and has not expired. Not all vaccines are available in every province, and healthcare providers should offer the available vaccine. 

Vaccines approved for use in Canada are the inactivated (trivalent and quadrivalent), recombinant quadrivalent, and live attenuated influenza (trivalent and quadrivalent) vaccines. Live vaccines are not recommended for people over 65. The inactivated and recombinant vaccines are administered intramuscularly. Standard influenza vaccines are available as single-dose pre-filled syringes (0.5 ml) and 5 ml multi-dose vials (the adult dose is 0.5 ml). The high-dose quadrivalent vaccine is available as a 0.7 ml pre-filled syringe. A trivalent adjuvanted influenza vaccine is available; no adjuvanted quadrivalent vaccine is available. Adults require only one dose of any influenza vaccine a year.

Older people have poorer immune responses to the influenza vaccine. Only 19 percent of people over 65 developed immunity to influenza after vaccination, compared to 60 percent of younger vaccinees. People over 65 should preferably receive high-dose or adjuvanted vaccines. You shouldn’t deny vaccination because of the non-availability of the preferred vaccines; offer a standard influenza vaccine. Drawing 0.7 ml from a multi-dose vial is inappropriate; the high-dose vaccine has a much higher concentration.

Influenza Vaccine — Adverse Effects

Fever is a common, expected adverse effect. It is usually mild and lasts less than 48 hours. Other adverse effects are malaise, chills, and fatigue. Injection site redness, tenderness, and swelling are also frequent. These are self-limiting, but acetaminophen (paracetamol) provides relief.

When administering vaccines, you should be prepared to manage any vaccine-related emergency, including anaphylaxis.

Influenza Vaccine — Contraindications

• An anaphylactic reaction to a dose of influenza vaccine. However, if hypersensitivity to a specific vaccine component is identified, another vaccine lacking that component may be considered. As always, maintain preparations for managing reactions.
• Guillan-Barre syndrome (GBS) within six weeks of an earlier dose unless another cause for the GBS was identified.
• The live attenuated influenza vaccine (LAIV) cannot be given to people with immunocompromise, severe asthma, and people over 65. Pregnant people should not receive any live vaccines.
• Egg allergy is not a contraindication.

Common Questions About Influenza Vaccination

Does the flu vaccine work?

Yes, the vaccine is effective, but its efficacy varies from year to year. It reduces disease severity, hospitalizations, and deaths among those who get influenza after vaccination.

Why is vaccination needed every year?

The influenza viruses change constantly. The World Health Organization monitors the types of virus strains and updates the composition of the vaccine twice a year. The vaccine is effective only if the vaccine has the same viruses as those causing disease in the community. Besides, vaccine-provided immunity wanes over time and annual vaccination provides the best protection.

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