Influenza virus undergoes frequent mutations causing antigenic drifts and shifts.
Requires updated vaccine composition annually to match circulating strains.
World Health Organization Global Influenza Surveillance and Response System monitors and updates composition twice yearly for northern and southern hemispheres.
Types Of Vaccines
Inactivated Influenza Vaccines
Comprise split-product vaccines produced from detergent-treated purified virus, or surface antigen subunit vaccines containing purified hemagglutinin and neuraminidase.
Quadrivalent vaccines contain two influenza A strains (H1n1 and H3n2) and two influenza B strains.
Administered via intramuscular route.
Demonstrate 63.2 percent efficacy against moderate-to-severe influenza in children 6 to 35 months of age.
Efficacy wanes over time, offering clinical protection for approximately 6 to 8 months.
Live-Attenuated Influenza Vaccines
Developed by repeated passage of viruses at low temperatures to form temperature-sensitive variants.
Virus replicates efficiently at 25 degrees Celsius but fails to replicate at core body temperatures of 37 to 39 degrees Celsius.
Administered intranasally using an accuspray device.
Exhibit overall efficacy of 82 percent against laboratory-confirmed influenza in healthy children.
Avoided in high-risk categories, immunocompromised individuals, and pregnant women.
Dosage And Administration Schedule
Parameter
Inactivated Influenza Vaccine
Live-Attenuated Influenza Vaccine
Minimum Age
6 months
2 years
Dose And Route
0.5 ml (15 µg); Intramuscular
0.25 ml in each nostril; Intranasal
First Time Vaccination (<9 Years)
Two doses spaced 4 weeks apart
Two doses spaced 4 weeks apart
First Time Vaccination (>=9 Years)
Single dose
Single dose
Revaccination
Single annual dose
Single annual dose
Indications And Target Groups
Recommended universally for children aged 6 months to 5 years.
Prioritized for high-risk children older than 5 years with chronic cardiac, pulmonary, renal, or liver diseases.
Indicated in congenital or acquired immunodeficiency, including human immunodeficiency virus infection.
Strongly recommended for pregnant women during any stage of pregnancy to protect mothers and young infants.
Optimum administration time in India is the pre-monsoon period (April to May) using the most recent available strains.
Contraindications And Precautions
Both vaccine types contraindicated in individuals with severe allergic reactions to previous doses or vaccine components.
Precaution required for individuals developing Guillain-Barre syndrome within 6 weeks of prior influenza vaccination.
Inactivated vaccines must be administered with extreme caution under medical supervision in patients with severe egg allergy.
Live-attenuated vaccines contraindicated during concomitant aspirin therapy, in children with wheezing episodes in the past 12 months, and following receipt of antiviral medications within 48 hours.
