Vaccine recommendations for children and youth for the 2023/2024 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 by helping families to recognize both the potential severity of influenza infection, and the efficacy and safety of vaccination.

WHO SHOULD BE VACCINATED?

The Canadian Paediatric Society (CPS) encourages annual influenza vaccinations for ALL children and youth 6 months of age or older, as well as people—including paediatricians and other health care providers—capable of transmitting influenza to those at high risk for complications^[1]. All children younger than 5 years of age are considered to be at high risk and, in addition, are efficient transmitters of influenza^[2].

This practice point summarizes the most recent recommendations from the National Advisory Committee on Immunization (NACI)^[1]. NACI recommends influenza vaccine for all individuals ≥6 months of age, 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)^[1].

WHY VACCINATE ANNUALLY?

Although some vaccinated individuals retain immunity from one season to the next, this is less likely when predominant circulating strains change. Strains used in the vaccine are updated frequently and annual revaccination is recommended. For the 2023/24 season, the A H1N1 component has been replaced, while the A H2N3 and the B components remain the same as for the 2022/23 season^[3].

While recent concerns about reduced vaccine efficacy after repeated vaccination are being investigated, data so far support continuing annual revaccination^[1].

INFLUENZA VACCINATION IN THE TIME OF COVID-19

In the ongoing pandemic, vaccination against influenza is especially important to minimize the impact of concurrent influenza and COVID-19 outbreaks on individuals and the health care system. NACI has issued guidance for influenza vaccine use during the COVID-19 pandemic^[4][5]. General guidance on immunization during the pandemic is also available^[6]. Local public health recommendations concerning screening for symptoms of respiratory infection and for exposure to COVID-19, physical distancing, hand hygiene, and use of masks and other personal protective equipment should be followed. The CPS has information on the use of facial coverings by children^[7].

NACI recommends that in the outpatient setting, vaccination of individuals with symptoms of acute respiratory infection should be deferred until the resolution of symptoms, given the possibility of unknowingly transmitting COVID-19 to others. However, a symptomatic patient who presents to an outpatient setting may be vaccinated at the discretion of the clinic^[4].

WHAT VACCINE SHOULD BE USED?

For several decades, influenza vaccines contained two subtypes of influenza A and one lineage of influenza B. Two lineages of influenza B have been in circulation simultaneously in recent years, and trivalent vaccines are now being replaced by quadrivalent vaccines containing two strains of influenza A and two lineages of influenza B. NACI recommends use of quadrivalent vaccines for children and adolescents because of the burden of influenza B disease in this age group.

Two types of influenza vaccines are licensed in Canada: inactivated influenza vaccines (IIV) for intramuscular (IM) injection and an intranasal, live attenuated influenza vaccine (LAIV) (see Table 1).

For the coming season, the only available standard dose IIV will be the quadrivalent form (IIV4-SD). An adjuvanted IIV3 (IIV3-Adj) is available for children 6 to 23 months of age. Adjuvants are designed to enhance vaccine immunogenicity, but this vaccine is not currently available in a quadrivalent form. Most IIV available in Canada are produced in eggs. A new type of IIV4, IIV4-cc, a vaccine produced in mammalian cell cultures rather than in eggs (Flucelvax, Seqirus Canada), is authorized for use in Canada in children 6 months of age and older and in adults^[1]. IIV4 produced using recombinant technology (Supemtek, Sanofi Pasteur) was authorized for adults 18 years of age and older in January 2021 but is not yet available for children.

LAIV is available only in the quadrivalent form. It is authorized for use in individuals 2 to 59 years of age. The most common side effects of LAIV are transient nasal congestion and rhinorrhea. LAIV is not licensed for use in children younger than 2 years of age because of a small, but significant, increased rate of wheezing 2 to 4 weeks following vaccination observed in this age group. LAIV can be used for children and youth, 2 to 17 years of age, who are not immunocompromised. NACI states that although IIV is preferred for children with human immunodeficiency virus (HIV), LAIV may be considered in selected children with well-controlled HIV (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, NACI recommends that either LAIV or IIV may be used. The American Academy of Pediatrics also recommends that either vaccine may be used^[8]. 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^[1].

In summary, quadrivalent influenza vaccine is recommended for all children. For non-immunocompromised children 2 years of age or older, either IIV or LAIV may be used. See Table 1for vaccine options and NACI preferences for children and youth. Programmatic considerations may affect vaccine availability in publicly funded programs.

WHEN TO VACCINATE

For maximum benefit, influenza vaccine should be given as soon as it is available, before the onset of the influenza season. Nevertheless, it should be offered to individuals who have not received it until the end of the current season. Benefit may be less if exposure to influenza has already occurred.

ARE THERE ANY CONTRAINDICATIONS TO INFLUENZA VACCINE?

An anaphylactic reaction to a previous dose of influenza vaccine 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^[1].

Since 2011/2012, egg allergy has not been a contraindication to the use of IIV. More recently, several studies have shown that LAIV can also be given safely to egg-allergic individuals and since 2016/2017, NACI no longer considers this condition a contraindication^[1]. Either IIV or LAIV can be given to individuals with egg allergy. Like all other vaccines, influenza vaccine should be given in a setting where anaphylaxis can be managed^[1].

LAIV, because it is a live vaccine, is contraindicated in individuals with immunocompromising conditions. The exception is children with stable HIV infection, for whom it 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 of age, who are receiving chronic acetylsalicylic acid-containing therapy, because Reye’s syndrome has been associated with acetylsalicylic acid given during influenza infection^[1].

For individuals experiencing nasal congestion sufficient to impede the appropriate delivery of LAIV, vaccination should be deferred until the congestion has resolved or IIV should be given^[1].

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^[1].

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

Any seasonal influenza vaccine, including LAIV, may be given at the same time as, or any time before or after, any COVID-19 vaccine or any other vaccines, or the respiratory syncytial virus monoclonal antibody nirsevimab^[1][9].

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 h after discontinuation of therapy, or IIV should be substituted^[1].

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)^[1].

The first year that a child younger than 9 years of age receives influenza vaccine (either IIV or LAIV), two doses at least 4 weeks apart are required. If a child less than 9 years of age has received at least one dose of any influenza vaccine in the past, only one dose is required this season. Children 9 years of age or older and adults require only one dose each year^[1].

CANADIAN PAEDIATRIC SOCIETY INFECTIOUS DISEASES AND IMMUNIZATION COMMITTEE

Members: Michelle Barton MD (Chair); Ari Bitnun MD; Sergio Fanella MD; Justin Penner MD; Raphael Sharon MD (Board Representative), Jeannette Comeau MD, MSC, FRCPC, FAAP

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

Principal author: Dorothy L. Moore MD

References

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.