Influenza may present as a mild respiratory illness similar to the common cold or it may present without characteristic signs and symptoms.
The main type of influenza virus are types A, B & C virus. Types A&B are the main causes of influenza outbreaks.
Patient may appear flushed and have pain on eye movement. Non-exudative pharyngitis, scattered rales or rhonchi may be present.


  • 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 2018/2019 flu season:
    • The recommended trivalent vaccine should contain an A/Michigan/45/2015 (H1N1)pdm09–like virus, an A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus, & a B/Colorado/06/2017–like virus (B/Victoria/2/87 lineage)
    • Quadrivalent vaccines will contain above 3 antigens, plus a B/Phuket/3073/2013–like virus (B/Yamagata/16/88 lineage)
    • Live attenuated virus vaccine 4 (LAIV4) is an option for patients in whom it is appropriate
  • 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


  • 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
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