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Influenza vaccines: Canadian Immunization Guide

For health professionals

Notice

The following guidance from the National Advisory Committee on Immunization (NACI) is available:

This chapter will not be updated to contain this information.

Last partial content update: May, 2025

This chapter was updated based on the following guidance from the National Advisory Committee on Immunization (NACI):

This information is captured in the table of updates.

On this page

Please note: The Public Health Agency of Canada (PHAC) recognizes that not all people giving birth or breastfeeding will identify as women or mothers. The writing in this chapter uses a gender additive approach where the term 'woman' is used alongside gender neutral language. This is intended to demonstrate a commitment to redress the historic exclusion of trans and non-binary people, whilst avoiding the risk of marginalizing or erasing the experience of women within the health care environment. However, in line with best practice, it is recognized that when discussing or caring for individuals in a one-on-one capacity, language and documentation should reflect the gender identity of the individual.

Key information

What

Who

How

Why

Epidemiology

Disease description

Infectious agent

There are 2 main types of influenza virus that cause seasonal epidemics in humans: A and B. Influenza A viruses are classified into subtypes based on 2 surface proteins: hemagglutinin (HA) and neuraminidase (NA). Three subtypes of HA (H1, H2, and H3) and 2 subtypes of NA (N1 and N2) are recognized among influenza A viruses as having caused widespread human disease over the past decades, most commonly A(H1N1) and A(H3N2).

Influenza B viruses are classified into 2 lineages that evolved in the early 1980s: B/Victoria and B/Yamagata. Historically, viruses from both lineages have contributed variably to influenza illness each year. As of March 2020, there have been no confirmed naturally occurring cases of B/Yamagata lineage virus infection worldwide.

Over time, antigenic variation (drift) of strains occurs within an influenza A subtype or a B lineage. Consequently, seasonal influenza vaccines need to be reformulated annually, to better match the circulating vaccine strains.

Reservoir

The primary reservoir of most influenza A viruses is wild birds. In humans, currently only 3 type/subtype viruses [A(H1N1), A(H3N2), and B], are circulating; for these, humans are the reservoir.

Transmission

Influenza is primarily transmitted by aerosols and droplets spread through coughing or sneezing, and through direct or indirect contact with respiratory secretions. The incubation period is usually about 2 days but can range from 1 to 4 days. Adults may be able to spread influenza to others from 1 day before symptom onset to approximately 5 days after symptoms start. Children and people with weakened immune systems may be infectious longer.

Risk factors

The people at greatest risk of influenza-related complications are adults and children with chronic health conditions, residents in long term and chronic care facilities, adults 65 years of age and older (particularly frail older adults), children 0 to 59 months of age, pregnant women and pregnant individuals, and individuals in or from First Nations, Inuit, or Metis communities.

Seasonal and temporal patterns

Seasonal influenza activity in Canada begins to increase over the fall, and peaks in the winter months. The influenza season can last for many months. Although 1 strain often predominates, more than 1 influenza strain typically circulates each season. Sporadic cases and occasional outbreaks may occur outside the typical influenza season.

Spectrum of clinical illness

Influenza infection may be asymptomatic or present as mild disease; conversely, it can manifest as severe disease and result in death. Symptoms typically include the sudden onset of fever, cough, and myalgia. Other common symptoms include headache, chills, loss of appetite, fatigue, and sore throat. Nausea, vomiting, and diarrhea may also occur, especially in children. Most people will recover within a week to 10 days. In some, influenza infection may lead to complications including pneumonia, respiratory failure, cardiovascular complications, or worsening of underlying chronic medical conditions. Influenza infection is also associated with an increased risk of myocardial infarction, stroke and Guillain-Barre syndrome (GBS).

Disease distribution

Each year, there are 3 to 5 million cases of severe illness, and 290,000 to 650,000 deaths from influenza worldwide.

Together, influenza and pneumonia are among the top 10 leading causes of death in Canada. Prior to the COVID-19 pandemic, influenza caused an estimated 15,000 hospitalizations annually in Canada, more than any other seasonal respiratory virus. Information on current influenza activity in Canada can be found on the FluWatch website.

Preparations authorized for use in Canada

Not all influenza vaccines authorized for use in Canada may be available.

Standard-dose, egg-based, trivalent inactivated influenza vaccine (IIV3-SD)

Standard-dose mammalian cell culture-based trivalent inactivated influenza vaccine (IIV-cc)

Adjuvanted inactivated trivalent influenza vaccine (IIV-Adj)

High-dose inactivated influenza vaccine (IIV-HD)

Live attenuated influenza vaccine (LAIV)

The following quadrivalent influenza vaccines may still be authorized for use in Canada but may not be marketed due to an ongoing transition to trivalent preparations:

Standard-dose, egg-based, quadrivalent inactivated influenza vaccine (IIV4-SD)

Standard-dose mammalian cell culture-based quadrivalent inactivated influenza vaccine (IIV-cc)

High-dose inactivated influenza vaccine (IIV-HD)

Recombinant influenza vaccine (RIV)

Live attenuated influenza vaccine (LAIV)

Trivalent vaccines contain 1 A(H1N1) strain, 1 A(H3N2) strain, and 1 influenza B strain from the Victoria-like lineage. Quadrivalent vaccines contain the strains in the trivalent vaccine plus an influenza B strain from the Yamagata lineage.

The antigenic characteristics of circulating influenza virus strains provide the basis for the World Health Organization's (WHO) recommendations for the strains selected for inclusion in each season's vaccine. Given the absence of the B/Yamagata lineage in recent years, the B/Yamagata virus strain is to be removed from influenza vaccine formulations. Manufacturers are in the process of transitioning to trivalent vaccines exclusively. Manufacturers that distribute influenza vaccines in Canada ensure the vaccines for the upcoming influenza season contain the WHO's recommended antigenic strains for the Northern Hemisphere. Vaccine producers may also use antigenically equivalent strains. Not all influenza vaccines authorized for use in Canada are available in Canada.

A summary of the characteristics of influenza vaccines available in Canada during the 2025-2026 influenza season can be found in Appendix B of the NACI Statement on Seasonal Influenza Vaccine. For complete prescribing information, consult the product monograph or information contained within Health Canada's authorized product monographs available through the Drug Product Database. Refer to Table 1 in Contents of Immunizing Agents Authorized for Use in Canada in Part 1 for a list of all vaccines authorized for use in Canada and their contents.

Immunogenicity, efficacy and effectiveness

Immunogenicity

Antibody response after vaccination depends on several factors, including the age of the recipient, prior and subsequent exposure to antigens, and the presence of immune compromising conditions. Vaccine-induced immune response is not as robust in young children, older adults and persons with immune compromising conditions as it is in other people. High-dose and adjuvanted influenza vaccines are designed to enhance the immune response in certain populations. Protective levels of humoral antibodies, which correlate with protection against influenza infection, are achieved approximately 2 weeks after vaccination; however, there may be some protection afforded before that time.

Efficacy and effectiveness

Influenza vaccine has been shown to be efficacious in providing protection against influenza infection and illness; however, the effectiveness of the vaccine can vary from season to season and by influenza vaccine strain type and subtype. Influenza vaccine effectiveness depends on how well the vaccine strains match with circulating influenza viruses, the type and subtype of the circulating virus, as well as the health and age of the individual receiving the vaccine. Nevertheless, even when there is a less-than-ideal match or lower effectiveness against 1 strain, vaccine recipients, particularly people at high risk of influenza-related complications and hospitalization, are still more likely to be protected compared to those who are unvaccinated. Among adults 65 years of age and older, IIV-HD, IIV-Adj, and RIV appear to have increased vaccine effectiveness as compared to IIV-SD.

In general, influenza vaccination in consecutive seasons does not have a negative or positive effect on vaccine effectiveness in comparison to vaccination in the current season only.

Recommendations for use

Routine schedule

Seasonal influenza vaccine should be offered annually to everyone 6 months of age and older who does not have contraindications to the vaccine, irrespective of vaccination in previous seasons. Table 1 provides age group-specific recommendations. Any of the age-appropriate influenza vaccine types available for use may be considered for people without contraindications to the vaccine.

Influenza vaccines do not confer sufficient protection to make the vaccine useful in infants less than 6 months of age. Children 6 months to less than 9 years of age who have not previously received at least 1 dose of the seasonal influenza vaccine require 2 doses of influenza vaccine, with a minimum of 4 weeks between doses. Only 1 dose of influenza vaccine per season is recommended for everyone else.

Vaccination before the onset of the influenza season is strongly preferred, as delayed administration may result in lost opportunities to prevent infection from exposures that occur prior to vaccination. However, influenza vaccine may still be administered until the end of the season.

Table 1: Recommendations for influenza vaccine type by age group
Recipient by age group Vaccine types authorized for use Recommendations
6 to 23 months
  • IIV3-Adj
  • IIV4-SD
  • IIV4-cc
 Any of the available influenza vaccines authorized for this age group should be used in infants and young children without contraindications to the vaccine. There is insufficient evidence to recommend Influvac Tetra (IIV4-SD) in children younger than 3 years of age.
2 to 17 years
  • IIV4-SD
  • IIV4-cc
  • LAIV4
 Any of the available age-appropriate influenza vaccines should be used in children without contraindications or precautions to the vaccine, including those with chronic health conditions. There is insufficient evidence to recommend Influvac Tetra (IIV4-SD) in children younger than 3 years of age.
  • LAIV may be given to children with:
    • stable, non-severe asthma
    • cystic fibrosis who are not being treated with immunosuppressive drugs (e.g., prolonged systemic corticosteroids)
    • stable HIV infection, i.e., if the child is currently being treated with ART for at least 4 months and has adequate immune function
  • LAIV should not be used in children or adolescents for whom it is contraindicated or for whom there are warnings and precautions such as those with:
    • severe asthma (defined as currently on oral or high-dose inhaled glucocorticosteroids or active wheezing)
    • medically attended wheezing in the 7 days prior to vaccination
    • current receipt of aspirin or aspirin-containing therapy
    • immune compromising conditions, with the exception of stable HIV infection, i.e., if the child is currently being treated with ART for at least 4 months and has adequate immune function
    • pregnancy
      • in pregnancy, a non-live vaccine (IIV-SD, IIV-cc or RIV) should be used instead
18 to 59 years
  • IIV4-SD
  • IIV4-cc
  • RIV4
  • LAIV4
 Any of the available influenza vaccines authorized for this age group should be used in adults 18 to 59 years without contraindications or precautions to the vaccine. LAIV is not recommended in pregnancy or for adults with any of the chronic health conditions identified in List 1, including immune compromising conditions, and health care workers. IIV or RIV should be used instead.
60 to 64 years
  • IIV4-SD
  • IIV4-cc
  • RIV4
 Any of the available influenza vaccines authorized for this age group should be used in adults 60 to 64 years without contraindications to the vaccine.
65 years and older
  • IIV3-Adj
  • IIV4-SD
  • IIV4-HD
  • IIV4-cc
  • RIV4
 If available, IIV-HD, IIV-Adj, or RIV should be preferentially offered to adults 65 years and older as these vaccines provide better protection than IIV-SD in this age group.
  • Where supply of IIV-HD, IIV-Adj, or RIV is limited, groups at highest risk of severe outcomes from influenza among adults 65 years and older may be prioritized for these vaccines, e.g., adults 75 years of age and older, those with 1 or more comorbidities, older frail adults, and residents of nursing homes and other chronic care facilities.

Abbreviations: ART: antiretroviral therapy; IIV: inactivated influenza vaccine; IIV3-Adj: adjuvanted trivalent inactivated influenza vaccine; IIV4-cc: quadrivalent mammalian cell culture-based inactivated influenza vaccine; IIV4-HD: high-dose quadrivalent inactivated influenza vaccine; IIV4-SD: standard-dose quadrivalent inactivated influenza vaccine; RIV4: quadrivalent recombinant influenza vaccine; LAIV4: quadrivalent live attenuated influenza vaccine.

Vaccination of specific populations

To reduce the morbidity and mortality associated with influenza, immunization programs may focus on people at high risk of influenza-related complications (refer to List 1: Groups for whom influenza vaccination is particularly important).

List 1: Groups for whom influenza vaccination is particularly important

People at high risk of influenza-related complications or hospitalization

  • All children 6 to 59 months of age
  • Adults and children with the following chronic health conditions:
    • Cardiac or pulmonary disorders (includes bronchopulmonary dysplasia, cystic fibrosis, and asthma)
    • Diabetes mellitus and other metabolic diseases
    • Cancer, immune compromising conditions (due to underlying disease, therapy, or both, such as solid organ transplant or hematopoietic stem cell transplant recipients)
    • Renal disease
    • Anemia or hemoglobinopathy
    • Neurologic or neurodevelopmental conditions (includes neuromuscular, neurovascular, neurodegenerative, neurodevelopmental conditions, and seizure disorders [and, for children, includes febrile seizures and isolated developmental delay], but excludes migraines and psychiatric conditions without neurological conditions)
    • Class 3 obesity (defined as BMI of 40 kg/m² and over)
    • Children 6 months to 18 years of age undergoing treatment for long periods with acetylsalicylic acid, because of the potential increase of Reye's syndrome associated with influenza
  • Pregnant women and pregnant individuals
  • People of any age who are residents of nursing homes and other chronic care facilities
  • Adults 65 years of age and older
  • Individuals in or from First Nations, Inuit, or Métis communities as a result of intersecting determinants of health rooted in historic and ongoing colonization and systemic racism

People capable of transmitting influenza to those at high risk

  • Health care workers and other care providers in facilities and community settings who, through their activities, are capable of transmitting influenza to those at high risk
  • Household contacts, both adults and children, of individuals at high risk, whether or not the individual at high risk has been vaccinated:
    • household contacts of individuals at high risk
    • household contacts of infants less than 6 months of age, as these infants are at high risk but cannot receive influenza vaccine
    • members of a household expecting a newborn during the influenza season
  • Those providing regular childcare to children 0 to 59 months of age, whether in or out of the home
  • Those who provide services within closed or relatively closed settings to people at high risk (e.g., crew on a cruise ship)

Others

  • People who provide essential community services
  • People whose occupational or recreational activities increase their risk of exposure to avian influenza A(H5N1) viruses

Children 6 months to 59 months of age

Young children have a high burden of influenza-associated illness. The risk of serious infection and hospitalization is highest among the very young. Because young children are less likely to have had prior exposure to an influenza virus, a 2-dose schedule is required to achieve protection for those less than 9 years of age that are previously unvaccinated.

Pregnant women and pregnant individuals

Influenza vaccine should be offered to all pregnant women and pregnant individuals at any stage of pregnancy. An age-appropriate non-live influenza vaccine (i.e., IIV-SD, IIV-cc or RIV) is particularly important in pregnancy. When a pregnancy extends over 2 influenza seasons, 2 doses of influenza vaccine may be received during the course of the pregnancy (one in each influenza season). There is an increased risk of influenza-associated morbidity and hospitalization in pregnancy, and evidence of adverse neonatal outcomes, including late pregnancy loss and stillbirth. Vaccination of pregnant women and pregnant individuals has been shown to protect the pregnant person and protect against stillbirth and infants being born small for gestational age. It also protects infants for the first few months of life from influenza and influenza-related complications. In addition to pregnant women and pregnant individuals, the influenza vaccine should be offered to household contacts and care providers of young infants, since infants less than 6 months of age are ineligible for influenza vaccine but at high risk of influenza-related illness.

Refer to Immunization in pregnancy and breastfeeding in Part 3 for additional information.

Older adults

Adults 65 years of age and older are at greater risk of more severe complications from influenza, and influenza-attributed mortality rates increase with age. High dose, adjuvanted or recombinant influenza vaccine (IIV-HD, IIV-Adj, RIV) formulations are recommended for adults 65 years of age and older as these vaccines appear to have increased vaccine efficacy or effectiveness as compared to the standard dose influenza vaccine in this age group. If a preferred product is not available, any of the available age-appropriate influenza vaccines should be used. Where supply of IIV-HD, IIV-Adj, or RIV is limited, consider prioritizing groups at highest risk of severe outcomes from influenza among older adults, such as advanced-age older adults (e.g., 75 years of age and older), those with 1 or more chronic health conditions, residents of nursing homes and other chronic care facilities, and older frail adults.

Residents in nursing homes or other chronic care facilities

Residents of nursing homes and other chronic care facilities often have 1 or more chronic health conditions and live in institutional environments that may facilitate the spread of influenza. For these reasons, residents who are adults 65 years of age and older may be prioritized for receipt of IIV-HD, IIV-Adj, or RIV if the supply of these vaccines is limited.

Refer to Immunization of patients in health care institutions in Part 3 for additional information.

Persons with chronic health conditions

Certain chronic health conditions are associated with increased risk of influenza-related complications and hospitalization. Refer to List 1: Groups for whom influenza vaccination is particularly important. Influenza infection in individuals with certain chronic diseases can also lead to an exacerbation of the chronic condition.

Refer to Immunization of persons with chronic diseases in Part 3 for additional information.

Immunocompromised persons

People who are immunocompromised have an increased risk of morbidity and mortality from influenza. It is particularly important for all people 6 months of age and older who are immunocompromised to receive an influenza vaccine every year. Although influenza vaccination can induce protective antibody levels in a substantial proportion of adults and children with immune compromising conditions, vaccine effectiveness may be lower than in healthy individuals.

Refer to Immunization of immunocompromised persons in Part 3 for additional information.

Individuals in or from First Nations, Inuit, or Métis communities

Influenza vaccination is particularly important for individuals in or from First Nations, Inuit, or Métis communities, regardless of their geographic location, because they tend to have higher rates of influenza-associated hospitalization. The increased risk of severe influenza among individuals in or from First Nations, Inuit, and Métis communities is a consequence of many factors including medical conditions resulting from intersecting determinants of health. These intersecting determinants of health include social, environmental, and economic factors, rooted in historic and ongoing colonization and systemic racism (i.e., structural inequity).

Health care workers, care providers and other workers

Influenza vaccination is recommended for health care workers (HCWs) and other care providers including regular visitors, emergency response workers, those who work in continuing care or long-term care facilities or residences, those who provide home care for people at high risk, and students of related health care services. HCWs and other care providers who are potentially capable of transmitting influenza to those at high risk should receive annual vaccination with any age appropriate non-live influenza vaccine, regardless of whether the high-risk individual has been vaccinated. Vaccination of HCWs and other care providers decreases the vaccinated person's risk of illness, as well as the risk of transmission of influenza to patients at high risk of influenza-associated complications. Vaccination of HCWs and residents of nursing homes is associated with decreased risk of influenza outbreaks. Annual influenza vaccination is considered an essential component of the standard of care for all HCWs.

To minimize the disruption of services during annual influenza epidemics, all people who provide essential community services should consider annual influenza vaccination, as it can decrease work absenteeism due to respiratory illnesses.

Seasonal influenza vaccination will not prevent avian influenza but it is recommended for people whose occupational or recreational activities increase their risk of exposure to avian influenza A(H5N1). Although seasonal influenza vaccines do not protect against avian influenza infection, they may reduce the risk of seasonal human and avian influenza co-infection and the theoretical potential for human-avian viral reassortment, leading to a human-transmissible virus with pandemic potential.

Refer to Immunization of workers in Part 3 for additional information.

Travellers

Influenza occurs year-round in the tropics. In temperate northern and southern countries, influenza activity generally peaks during the winter season (November to March in the Northern Hemisphere and April to October in the Southern Hemisphere). Influenza vaccine should be offered to travellers.

Vaccines prepared specifically for use in the Southern Hemisphere are not available in Canada, and the extent to which recommended vaccine components for the Southern Hemisphere may overlap with those in available Canadian formulations will vary. A decision for or against revaccination of travellers to the Southern Hemisphere between April and October, if they had already been vaccinated in the preceding fall or winter with the Northern Hemisphere's vaccine, depends on individual risk assessment, the similarity between the Northern and Southern Hemisphere vaccines, the similarity between the Northern Hemisphere vaccine strains and currently circulating strains in the Southern Hemisphere, and the availability of a reliable and safe vaccine at the traveller's destination.

Refer to Immunization of travellers in Part 3 for additional general information.

Serologic testing

Serologic testing is not necessary or recommended before or after receiving seasonal influenza vaccine.

Administration practices

Dose and route of administration

The dose and route for influenza vaccines vary and are detailed in the product monographs.

Refer to Vaccine administration practices in Part 1 for additional information.

Concurrent administration with other vaccines

All influenza vaccines, including LAIV, may be given at the same time (i.e., same day) as, or at any time before or after, administration of another live or non-live vaccine for those aged 6 months and older.

Refer to the COVID-19 vaccines chapter for latest guidance on concurrent administration of influenza vaccine with COVID-19 vaccines. For more information regarding vaccine timing, refer to Timing of vaccine administration in Part 1.

Interchangeability of vaccines

If a child aged less than 9 years requires 2 doses of influenza vaccine in the same influenza season, it is preferable to use the same type of vaccine for both doses. However, if the type of vaccine used for the first dose is not available for the second dose, a different type of influenza vaccine may be provided. For more information refer to Principles of vaccine interchangeability in Part 1.

Pre- and post-vaccination counselling

Refer to Vaccine administration practices in Part 1 for information on pre- and post-vaccination counseling, vaccine preparation and administration technique, and infection prevention and control.

Storage requirements

Influenza vaccines should be stored at +2°C to +8°C and should not be frozen. For additional information, consult the product monographs available through Health Canada's Drug Product Database. Refer to Storage and handling of immunizing agents in Part 1 for additional information.

Safety and adverse events

Common and very common adverse events

Common adverse events occur in 1% to less than 10% of vaccinees. Very common adverse events occur in 10% or more of vaccinees.

With IM-administered influenza vaccines, mild and transient injection site reactions e.g., soreness at the injection site lasting up to 2 days, are common. Any systemic reactions e.g., myalgia, headache, fatigue and malaise, are usually mild and short-lived. Influenza vaccines with adjuvant tend to produce more extensive injection site reactions than unadjuvanted, but these reactions are also generally mild and resolve within a few days. IIV-HD tends to induce higher rates of systemic reactions compared to IIV-SD, but most of these reactions are also mild and short-lived. The most common adverse reactions experienced by recipients of LAIV are nasal congestion and runny nose.

Uncommon, rare and very rare adverse events

Uncommon adverse events occur in 0.1% to less than 1% of vaccinees. Rare and very rare adverse events occur, respectively, in 0.01% to less than 0.1% and less than 0.01% of vaccinees.

Serious adverse events are rare following influenza vaccination, and in most cases, data are insufficient to determine a causal association. Allergic responses to influenza vaccine are a rare consequence of hypersensitivity to some components of the vaccine or its container.

Other reported adverse events and conditions

Guillain-Barré syndrome

Studies suggest that the absolute risk of Guillain-Barré syndrome (GBS) in the period following seasonal and A(H1N1) pdm09 influenza vaccination is about 1 excess case per million vaccinations, and that the risk of GBS associated with influenza illness (about 17 cases per million influenza-coded health care encounters, which are a proxy for influenza illness) is higher than that associated with influenza vaccination.

Although the evidence considering influenza vaccination and GBS is inadequate to accept or reject a causal relation between GBS in adults and seasonal influenza vaccination, avoiding subsequent influenza vaccination of individuals known to have had GBS without other known etiology within 6 weeks of a previous influenza vaccination appears prudent at this time. However, the potential risk of GBS recurrence associated with influenza vaccination must be balanced against the risk of GBS associated with influenza infection itself and the benefits of influenza vaccination.

Oculorespiratory syndrome

Oculorespiratory syndrome (ORS) consists of bilateral red eyes and 1 or more associated respiratory symptoms (cough, wheeze, chest tightness, difficulty breathing, difficulty swallowing, hoarseness, or sore throat) that starts within 24 hours of vaccination, with or without facial edema. ORS was first identified during the 2000 - 2001 influenza season. Since then, there have been far fewer cases per year. ORS is not considered to be an allergic response. People who have an occurrence or recurrence of ORS upon vaccination do not necessarily experience further episodes with future vaccinations. Individuals who have experienced ORS without lower respiratory tract symptoms may be safely revaccinated with influenza vaccine. Individuals who have experienced ORS with lower respiratory tract symptoms should seek medical advice.

Guidance on reporting adverse events following immunization

To ensure the ongoing safety of vaccines in Canada, reporting of adverse events following immunization (AEFIs) by vaccine providers and other clinicians is critical, and in some jurisdictions, reporting is mandatory under the law.

Vaccine providers are asked to report AEFIs through local public health officials and to check for specific AEFI reporting requirements in their province or territory. In general, any serious or unexpected adverse event felt to be temporally related to vaccination should be reported.

For influenza vaccines, the following AEFIs are of particular interest:

Refer to Vaccine safety and pharmacovigilance and Adverse Events Following Immunization (AEFI) in Part 2 for additional information on vaccine safety and for definitions of AEFIs, and reporting of AEFIs to public health.

Contraindications and precautions

Influenza vaccines are contraindicated in persons with a history of anaphylaxis after previous administration of the vaccine and in persons with proven immediate or anaphylactic hypersensitivity to any component, except egg, of the specific vaccine or its container. Refer to Contents of immunizing agents authorized for use in Canada in Part 1 for a list of all vaccines authorized for use in Canada and their contents.

Safety data confirm that egg-allergic individuals may be vaccinated against influenza using any influenza vaccine, including egg-based vaccines and LAIV, without prior influenza vaccine skin test and with the full dose, irrespective of a past severe reaction to egg and without any particular considerations, including vaccination setting.

Additional contraindications apply to the use of LAIV in people with certain health conditions:

Precautions for the use of LAIV are as follows:

As a precaution, influenza vaccination should be avoided in people who have developed GBS within 6 weeks of a previous influenza vaccination. Medical advice may be sought to balance the potential risk of GBS recurrence associated with influenza vaccination against the risk of GBS associated with influenza infection itself, and the benefits of influenza vaccination.

ORS is usually transient, resolving within 48 hours of onset. The only associated precaution is when lower respiratory symptoms accompany ORS, in which case expert review is required prior to subsequent immunization.

Influenza vaccination should not be delayed because of minor or moderate acute illness, with or without fever; however, in people with serious acute illnesses it may be postponed until their symptoms have abated.

Refer to Contraindications and precautions in Part 2 for additional information.

Other considerations

Drug interactions

Although influenza vaccine can inhibit the clearance of warfarin and theophylline, clinical studies have not shown any adverse effects attributable to these drugs in people receiving influenza vaccine. Statins have effects on the immune system in addition to their therapeutic cholesterol-lowering actions. Two published studies have found that adults who are regular statin users had an apparent decreased response to influenza vaccination as measured by reduced geometric mean titres (GMT) or reduced vaccine effectiveness against medically attended acute respiratory illness. Statins are widely used in the same adult populations who are also at-risk for influenza-related complications and hospitalizations. Therefore, if these preliminary findings are confirmed in future studies, concurrent statin use in adult populations could have implications for influenza vaccine effectiveness and how this use is assessed in the measurement of vaccine effectiveness.

Chapter revision process

This chapter was updated based on the Statement on seasonal influenza vaccine for 2025-2026, from the National Advisory Committee on Immunization (NACI).

Acknowledgments

This chapter was based on a NACI statement prepared by A Sinilaite and W Siu on behalf of the NACI Influenza Working Group. The chapter was prepared by F Crane and S Pierre and reviewed by W Siu, J Papenburg and C Jensen.

NACI gratefully acknowledges the contribution of: N Haddad.

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