• Vaccines are the primary preventive measure against influenza
• Vaccine used should comply with current World Health Organization (WHO) recommendations
  • Annual seasonal influenza vaccination is recommended for all pediatric patients ≥6 months of age
    • Highly recommended for pediatric patients at increased risk for complications (ie patients with asthma, cardiac disease, immunosuppression, neurodevelopmental disorders)

Influenza Vaccine

• For the 2017/2018 flu season:
  • The recommended trivalent vaccine should contain an A/Michigan/45/2015 (H1N1)pdm09–like virus, an A/Hong Kong/4801/2014 (H3N2)-like virus, & a B/Brisbane/60/2008–like virus (Victoria lineage)
  • Quadrivalent vaccines will contain above 3 antigens, plus a B/Phuket/3073/2013–like virus (Yamagata lineage), same as in the last flu season
  • Both trivalent & quadrivalent vaccines are available for intramuscular injection for the 2017-2018 season
  • LAIV4 is still not recommended for the 2017/2018 flu season, due to concerns about its efficacy against(H1N1)pdm09 viruses in the recent seasons
• Dosing depends on child's age during 1st dose & immunization history
  • Children ≥9 years old requires only 1 dose
  • For children 6 months - 8 years old:
    • 2 doses are needed if given <2 doses before July 1, 2017
    • 1 dose needed if already received ≥2 total doses before July 1, 2017

Composition:

• WHO has a global influenza surveillance program
  • The collaborating centers provide early warning system for emerging strains of influenza that have epidemic potential
  • This system is necessary to create effective vaccines that contain the current circulating strains

• Valency & composition depends upon the number & type of strains covered by the vaccine:
  • Trivalent vaccines: contains 2 type A strains & 1 type B strain of influenza
  • Quadrivalent vaccines: contains 2 type A strains & 2 type B strains of influenza
  • Recommended vaccine composition is issued yearly by WHO in March for vaccines used in the southern hemisphere & in October for vaccines in the northern hemisphere

• Equatorial regions will need to use epidemiological considerations to determine which recommendations (March or October) are appropriate for their region

Inactivated Influenza Vaccine [Intramuscular (IM) or Deep Subcutaneous (SC)]

• Uses vaccine composition issued by WHO in March (southern hemisphere) & in October (northern hemisphere)
• Various types of inactivated influenza vaccine have been formulated to increase immunogenicity: split-virion,whole-virion, surface-antigen/adjuvant containing vaccines (eg aluminum, monophosphoryl lipid, virosome)
• If the vaccine used contains the predominant circulating influenza strains, the vaccine can be 70-90% effective in preventing illness in healthy adults
• Patients with concurrent medical conditions may have a reduced rate of severe respiratory illness & death (up to 50%)
  • Main benefit of vaccination in these patients is the prevention of severe consequences of infection rather than preventing uncomplicated illness
• Vaccines that conform to international standards of purity & potency are usually free from systemic side effects
• For individuals with history of egg allergy, the AAP & ACIP recommend to proceed with administration of influenza vaccine, although ACIP recommends specific situations based on previous symptoms:
  • Presence of hives/urticaria only should not be a contraindication
  • Those who experienced symptoms other than hives (eg angioedema, respiratory distress, lightheadedness, recurrent emesis) & needed Epinephrine or other medical interventions may receive influenza vaccine
  • Severe allergic reaction is a contraindication for vaccination with any form of influenza virus
  • A 15-minute observation period is recommended following administration of any vaccine
  • Patients/guardians who refuse egg-based vaccines may receive recombinant or cell-cultured products

Live, Attenuated Influenza Vaccine (Intranasal)

• Approved in some countries for the following uses:
  • Option for vaccination of healthy persons aged 2-49 years old
  • May be used in healthy individuals aged 2-49 years in close contact with high-risk groups except those in close contact with immunocompromised patients, or children aged 2-4 years diagnosed with asthma or with wheezing episode within the past 12 months