National Advisory Committee on Immunization (NACI). Canadian Immunization Guide Chapter on Influenza and Statement on Seasonal Influenza Vaccine for 2019–2020. Government of Canada. Published May 2019. Accessed October 2020. https://www.canada.ca/en/public-health/services/publications/vaccines-immunization/canadian-immunization-guide-statement-seasonal-influenza-vaccine-2019-2020.html
Specific vaccination recommendations vary among countries or even within a given country. Local or country-specific guidelines should be consulted.
1. Vaccines: Trivalent influenza vaccine (TIV) and quadrivalent influenza vaccine (QIV) are inactivated vaccines. The trivalent vaccine contains 3 antigens (influenza A H3N2, influenza A H1N1, and 1 influenza B lineage strain), while the quadrivalent vaccine contains the 2 A antigens from the trivalent vaccine along with 2 B antigens.
2. Indications: Seasonal influenza vaccine is recommended for the following individuals at increased risk for complications of influenza:
1) All persons ≥65 years of age.
2) Residents of nursing homes and other chronic care facilities (regardless of age).
3) Patients with cardiac or pulmonary disorders (including bronchopulmonary dysplasia, cystic fibrosis, and asthma).
4) Patients with diabetes mellitus and other metabolic diseases, renal disease, anemia or hemoglobinopathy, liver disease, cancer or immune compromising condition (due to underlying disease, therapy, or both), morbid obesity (body mass index [BMI] ≥40).
5) Individuals with neurologic or neurodevelopmental conditions, including neuromuscular, neurovascular, neurodegenerative, and neurodevelopmental conditions as well as seizure disorders (for children, also febrile seizures and isolated developmental delay) but excluding migraines and psychiatric conditions without neurologic conditions.
6) All pregnant women.
7) Persons who may be a potential source of infection for all high-risk patients listed above: the personnel of nursing homes and long-term care facilities, caregivers or household members of high-risk patients, health-care personnel (also administrative staff and medical students who are in contact with patients).
8) Children 6 months to 18 years of age undergoing treatment for long periods with acetylsalicylic acid (ASA), because of the potential increased risk of Reye syndrome associated with influenza.
9) All children 6 to 59 months of age.
10) Indigenous people.
Influenza vaccine is also recommended for people capable of transmitting influenza to those at high risk, including the following:
1) Health-care and other care providers in facilities and community settings who, through their activities, are capable of transmitting influenza to those at high risk.
2) Household contacts, both adults and children, of individuals at high risk, regardless of whether the individual at high risk has been vaccinated. This includes household contacts of individuals in high-risk groups, household contacts of infants <6 months of age (as infants are at high risk but cannot receive influenza vaccine), and members of a household expecting a newborn during the influenza season.
3) Those providing regular childcare to children 6 to 59 months of age, whether in or out of the home.
4) Those who provide services within closed or relatively closed settings to people at high risk (eg, crew on a ship).
Other groups who should receive influenza vaccine include people who provide essential community services and people who are in direct contact with poultry infected with avian influenza during culling operations.
In Canada and the United States, influenza vaccine is also recommended for anyone aged ≥6 months in order to reduce the risk of influenza.
Indications for specific types of vaccines: QIV is preferred over TIV, which can be used when QIV is unavailable. Inactivated vaccines are available in high-dose or standard-dose formulations. High-dose formulations are indicated only for those ≥65 years. An adjuvanted vaccine is also indicated for those ≥65 years. There is also a live attenuated influenza vaccine (LAIV), available in quadrivalent formulation indicated for children and adolescents aged 2 to 17 years.
3. Contraindications to TIV or QIV include an anaphylactic reaction to a previous dose of inactivated influenza vaccine. Particular caution should be taken in patients who have developed Guillain-Barré syndrome (GBS) within 6 weeks of a prior influenza vaccination (a relative contraindication). However, the risk of repeated GBS after vaccination is very low, while an influenza-like illness is associated with an >16-fold increase in the risk of developing GBS within 1 month of the infection; influenza is associated with a 17-fold increase in the risk of GBS compared with persons receiving influenza vaccination. Individuals with egg allergies may be vaccinated against influenza using inactivated TIV, inactivated QIV, or LAIV without a prior influenza vaccine skin test and with the full dose, irrespective of a past severe reaction to egg and without any extraordinary precautions, but ensuring that, as for any vaccine administration, health-care providers be prepared with the necessary equipment, knowledge, and skills to respond to a vaccine emergency at all times. Contraindications to LAIV include severe asthma, medically attended wheezing in the 7 days prior to vaccination, current receipt of ASA-containing therapy, and immune compromising conditions.
4. Immunization schedule in adults: Vaccination should be repeated annually using a vaccine updated for the current influenza season. Optimally, vaccination should be performed in early fall in the northern hemisphere, prior to the increase in the incidence of influenza. If this is not possible, the vaccine should be administered on the first possible occasion (it may be administered throughout the influenza season).