Vaccine recommendations for children and youth for the 2024/2025 influenza season

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Paediatricians and other health care providers caring for children and youth have important roles in promoting influenza vaccination. They can increase the uptake of influenza vaccine (Inf-v) by helping families to recognize both the potential severity of influenza infection, and the efficacy and safety of vaccination. Vaccination against influenza is especially important to minimize the impacts of concurrent influenza and COVID-19 outbreaks on the health care system and on individuals.

This practice point summarizes recent recommendations from the National Advisory Committee on Immunization (NACI)^[2]. 

WHO SHOULD BE VACCINATED?

NACI recommends Inf-v for all individuals ≥6 months old, with particular focus on people at high risk for influenza-related complications or hospitalization, and individuals capable of transmitting influenza to those at high risk (Box 1)^[2].The Canadian Paediatric Society (CPS) encourages annual influenza vaccinations for ALL children and youth ≥6 months old, as well as people – including paediatricians and other health care providers – who may transmit influenza to those at high risk^[2]. Children younger than 5 years old are considered to be at high risk and, in addition, are efficient transmitters of influenza^[3].

Box 1. NACI recommendations

Influenza vaccination is particularly recommended for the following groups: People at high risk for influenza-related complications or hospitalization All children 6 to 59 months of age All children ≥6 months old, adolescents and adults with chronic health conditions (severe enough to require regular medical follow-up or hospital care), specifically: Cardiac or pulmonary disorders, including bronchopulmonary dysplasia, cystic fibrosis, asthma Diabetes mellitus and other metabolic diseases Cancer, other immune-compromising conditions (due to underlying disease, therapy, or both) Renal disease Anemia or hemoglobinopathy Neurological or neurodevelopmental conditions* Morbid obesity (body mass index ≥40 kg/m²) Children and adolescents (6 months to 18 years old) undergoing prolonged treatment with acetylsalicylic acid, because of the potential increase of Reye’s syndrome associated with influenza Indigenous peoples All residents of chronic care facilities All pregnant individuals, including adolescents, in all trimesters (for their own protection and to protect their infant after birth) All adults ≥65 years of age People capable of transmitting influenza to individuals at high risk, specifically: Household contacts (adults and children) of individuals at high risk (listed above), regardless of whether the person at risk has been immunized Household contacts of infants <6 months of age (these infants are at high risk but too young to receive Inf-v) Members of a household expecting a newborn (birth, adoption, or fostering) during influenza season Individuals providing regular child care to children ≤59 months of age, regardless of whether in- or out-of-home 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 Others providing services to individuals at high risk in closed or relatively confined settings (e.g., camps, cruise ships) Others People providing essential community services People in direct contact during culling operations with poultry infected with avian influenza

* These include neuromuscular, neurovascular, neurodegenerative, neurodevelopmental conditions and seizure disorders, and for children, febrile seizures and isolated developmental delay, but excludes migraines and neuropsychiatric conditions without neurological abnormalities.

WHY VACCINATE ANNUALLY?

The immune response to influenza may not persist beyond a year and circulating strains change frequently. Strains in the vaccines usually require updating annually. For the 2024/25 season, the A H3N2 component has been replaced, while the A H1N1 and the B components remain the same as for the 2023/24 season^[4].

WHAT VACCINE SHOULD BE USED?

For several decades, Inf-v contained two subtypes of influenza A and one lineage of influenza B. When annual circulation of two influenza B lineages became frequent, trivalent vaccines (tri-v) were replaced with quadrivalent vaccines (quad-v) containing two lineages (Victoria and Yamagata) of influenza B. NACI then recommended preferential use of quad-v for children and adolescents because of the higher burden of influenza B disease in this group compared with adults.

Since March 2020, the B/Yamagata lineage has disappeared worldwide and only the B/Victoria lineage has been circulating. In September 2023, the World Health Organization (WHO) recommended the removal of the B/Yamagata lineage from the annual Inf-v and the transition from quad-v to tri-v. The B/Yamagata component is no longer required and there is a theoretical risk of accidentally reintroducing this lineage into humans during the manufacturing process, which requires live virus, or by the use of live attenuated influenza vaccine (LAIV) containing the Yamagata strain^[1].

Two types of Inf-v are licensed in Canada: inactivated influenza vaccines (IIV) for intramuscular (IM) injection and an intranasal LAIV (see Table 1).

It is anticipated that for the coming season, the only standard dose IIV available in Canada will be the quadrivalent form (IIV4-SD) because manufacturers need time to re-adapt to the production of tri-v. However, tri-v may be used for children if it becomes available. Both tri-v and quad-v remain effective and safe for the individual being vaccinated^[1][2]. An adjuvanted IIV3 (IIV3-Adj; Fluad, Seqirus) is available for children 6 to 23 months old and for adults ≥65 years old. Most IIV available in Canada are produced in eggs. A vaccine produced in mammalian cell cultures (IIV4-cc; Flucelvax, Seqirus) is authorized for use in individuals ≥6 months old^[2]. A vaccine produced using recombinant technology (RIV4; Supemtek, Sanofi Pasteur) was authorized for adults ≥18 years old in January 2021, but is not yet available for children^[2].

LAIV is currently available only in the quadrivalent form. LAIV is authorized for use in individuals 2 to 59 years old. The most common side effects of LAIV are transient nasal congestion and rhinorrhea. LAIV is not licensed for use in children <2 years old because of an observed small, but significant, increased rate of wheezing 2 to 4 weeks following vaccination. LAIV can be used for children and youth, 2 to 17 years old, who are not immunocompromised. NACI states that although IIV is preferred, LAIV may be considered in selected children with well-controlled human immunodeficiency virus (HIV) infection (defined in Table 1) who will not accept IIV. Recent studies have shown comparable protection of children with LAIV and IIV. For children without contraindications to LAIV, either vaccine may be used^[2]. In adults, there is some evidence that IIV may be more efficacious than LAIV. Either IIV or LAIV may be used for healthy adults, but adults with chronic health conditions should receive IIV ^[2]. Vaccine options and NACI preferences for children and youth are shown in Table 1^[1][2].

Table 1. Choice of influenza vaccine for selected age and risk groups*
Age group, health profile	Vaccine types available	Comments
Children 6 to 23 months old	IIV4-SD IIV4-cc IIV3-Adj	IIV3-SD may also be used, if available
Children 2 to 17 years old: healthy or with chronic health conditions without immune compromise †	IIV4-SD IIV4-cc LAIV4	IIV3-SD may also be used, if available LAIV3 may also be used, if available (See contraindications to use of LAIV)
Children 2 to 17 years old: immune compromising conditions †	IIV4-SD IIV4-cc	IIV3-SD may also be used, if available LAIV is contraindicated
Pregnancy	IIV4-SD IIV4-cc	IIV3-SD may also be used, if available LAIV is not recommended (not studied; theoretical risk to fetus of live vaccine)
IIV Inactivated influenza vaccine; IIV3-Adj Adjuvanted trivalent inactivated influenza vaccine; IIV4 Quadrivalent inactivated influenza vaccine; IIV3-SD Standard-dose trivalent inactivated influenza vaccine; IIV4-SD Standard-dose quadrivalent inactivated influenza vaccine; IIV4-cc Cell culture-based quadrivalent inactivated influenza vaccine; LAIV Live attenuated influenza vaccine; LAIV3 Trivalent live attenuated influenza vaccine; LAIV4 Quadrivalent live attenuated influenza vaccine * For vaccine options for adults see references[1][2]. † LAIV may be considered for children with stable HIV infection who: have been receiving highly active antiretroviral therapy for ≥4 months; have a CD4 count ≥500/μL if age 2–5 years or ≥200/μL if age 6–17 years; and have an HIV plasma RNA level of <10,000 copies/mL (CD4 count and HIV plasma RNA level measured within 100 days before administration of LAIV)[2]

WHEN TO VACCINATE

For maximum benefit, Inf-v should be given as soon as it is available, before the onset of the influenza season. Nevertheless, Inf-v should be offered up to the end of the current influenza season to individuals who have not received it^[2].

ARE THERE ANY CONTRAINDICATIONS TO INFLUENZA VACCINE?

An anaphylactic reaction to a previous dose of Inf-v or to any of the components of the vaccine (with the exception of egg), or onset of Guillain-Barré syndrome within 6 weeks of influenza vaccination without other known cause, are contraindications to further doses^[2].

Studies have shown that IIV and LAIV can be given safely to egg-allergic individuals. An egg allergy is not a contraindication to administering either IIV or LAIV^[2]. Inf-v should be given in a setting where anaphylaxis can be managed^[2].

LAIV, because it is a live vaccine, is contraindicated in immunocompromised individuals. The exception is children with stable HIV infection, for whom LAIV may be considered. LAIV is also contraindicated for individuals with severe asthma (defined as current active wheezing or currently on oral or high-dose inhaled glucocorticosteroids, or medically attended wheezing within the previous 7 days), during pregnancy, and for children and adolescents, 2 to 17 years old, who are receiving chronic acetylsalicylic acid-containing therapy, because Reye’s syndrome has been associated with acetylsalicylic acid given during influenza infection^[2].

For individuals experiencing nasal congestion sufficient to impede the appropriate delivery of LAIV, vaccination should be deferred until this congestion has resolved, or IIV should be given^[2].

Spread of the vaccine virus from persons immunized with LAIV can occur; however, the virus is cold-adapted and, therefore, not very pathogenic. As a precaution, it is recommended that contact with severely immunocompromised patients (such as recent hematopoietic stem cell transplant recipients who still require isolation) be avoided for 2 weeks following receipt of LAIV. IIV is preferred for health care workers, family members, and others who will be in close contact with such individuals^[2].

CAN INFLUENZA VACCINE BE GIVEN AT THE SAME TIME AS OTHER VACCINES OR ANTIVIRAL PRODUCTS?

Any seasonal Inf-v may be given at the same time as, or any time before or after, any other vaccine(s) or the respiratory syncytial virus monoclonal antibodies nirsevimab^[5] or palivizumab^[6]. 

LAIV should not be administered until 48 hours after antiviral agents active against influenza have been discontinued because these antivirals will inactivate the vaccine virus. If an anti-influenza agent must be given within 2 weeks after the receipt of LAIV, another dose of vaccine should be administered at least 48 hours after discontinuation of therapy, or IIV should be substituted^[2].

WHAT IS THE DOSAGE?

The dose of IIV administered IM is 0.5 mL, regardless of age, except for paediatric IIV3-Adj, for which the dose is 0.25 mL IM. The dose of LAIV4 is 0.2 mL (0.1 mL administered in each nostril as an intranasal spray)^[2].

The first year that a child younger than 9 years old receives Inf-v (IIV or LAIV), two doses at least 4 weeks apart are required. If a child less than 9 years old has received at least one dose of any Inf-v in the past, only one dose is required this season. Children ≥9 years old and adults require only one dose each year^[2].

CANADIAN PAEDIATRIC SOCIETY INFECTIOUS DISEASES AND IMMUNIZATION COMMITTEE (2024-2025)

Members: Michelle Barton MD (Chair), Laura Sauvé MD (Past Chair), Eugene Ng MD (Board Representative), Sean Bitnun MD, Sergio Fanella MD, Justin Penner MD, Jeannette Comeau MD

Liaisons: Dorothy L. Moore MD (National Advisory Committee on Immunization), Sean Bitnun MD (Canadian Paediatric and Perinatal HIV/AIDS Research Group), Isabelle Viel-Thériault MD (Committee to Advise on Tropical Medicine and Travel), Marina Salvadori MD (Public Health Agency of Canada), Sean O’Leary (American Academy of Pediatrics, Committee on Infectious Diseases), Rupeena Purewal MD (Immunization Monitoring Program, ACTive), Cora Constantinescu MD (Association of Medical Microbiology and Infectious Disease Canada, Pediatric Committee)

Principal author: Dorothy L. Moore MD

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References

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Disclaimer: The recommendations in this position statement do not indicate an exclusive course of treatment or procedure to be followed. Variations, taking into account individual circumstances, may be appropriate. Internet addresses are current at time of publication.