Influenza vaccine !
Seasonal vaccine against influenza A and B. Its composition is updated every year because the virus's surface proteins keep changing.
Updated 2026-11-01
Also called: Inactivated influenza vaccine (IIV), Recombinant influenza vaccine (RIV), Live attenuated influenza vaccine (LAIV, intranasal)
The figure shows haemagglutinin from the 2009 pandemic H1N1 virus; vaccine antibodies are mainly directed against this protein.
Mechanism of action
Haemagglutinin binds the virus to sialic acid on respiratory cells, and neuraminidase releases new virions. The vaccine induces antibodies mainly against haemagglutinin. Small point mutations in these proteins (antigenic drift) produce new strains each season, so composition is reviewed and vaccination repeated every year; a major exchange of genes between influenza A viruses (antigenic shift) can cause a pandemic.
- The vaccine presents the season's haemagglutinin and neuraminidase
- Antibodies against haemagglutinin block attachment to respiratory cells
- Antigenic drift makes last season's antibodies less useful
- Composition is updated and the vaccine is repeated every season
Pharmacokinetics
- Onset and duration
- Immunity usually lasts less than one season, because antibodies wane and the virus drifts
Indications
- Seasonal prevention of influenza, especially in groups at risk of complications
- Pregnant women, to protect mother and newborn; MinSalud promotes it during pregnancy
- Indirect reduction of influenza-related pneumonia Community-acquired pneumonia →
Adverse effects
Common
- Pain and redness at the injection site
- Low-grade fever, myalgia, malaise
Contraindications
- Severe allergic reaction to a previous dose or a component
- Live intranasal vaccine: pregnancy and immunosuppression (the inactivated vaccine is used instead)
Key interactions
- Immunosuppressive therapy
- The live intranasal vaccine is avoided; inactivated or recombinant vaccine is used
- Acetylsalicylic acid in children
- Avoided in children and adolescents with influenza because of Reye syndrome
What is monitored
- History of Guillain-Barré syndrome within six weeks of a previous influenza vaccine (a precaution)
- Reaction after the dose
Administration and safety
- Inactivated and recombinant vaccines by intramuscular route; the live vaccine by intranasal spray
- Check the season's formulation and the product's age indication
- Some egg-based products contain residual egg protein, and some multidose vials contain thimerosal: read the product label
- Record the batch and product
Nursing care
- Ask about previous reactions and Guillain-Barré syndrome after an influenza vaccine
- Check pregnancy and immune status before choosing the live intranasal vaccine
- Explain that the vaccine does not cause influenza and must be repeated every season
- Remind families not to give acetylsalicylic acid to children with influenza
Pregnancy and breastfeeding
Inactivated or recombinant influenza vaccine is recommended in pregnancy and can be given in any trimester; the live intranasal vaccine is contraindicated.
Test yourself
Think of the answer, then tap the question to see it.
Why is the influenza vaccine given every year?
Antigenic drift changes haemagglutinin and neuraminidase each season, and immunity wanes in less than a year.
What is the difference between antigenic drift and antigenic shift?
Drift is gradual point mutation (seasonal epidemics); shift is an abrupt change from gene exchange between influenza A viruses (pandemics).
Which influenza vaccine is avoided in pregnancy?
The live attenuated intranasal vaccine; inactivated or recombinant vaccines are used.
Related drugs
Related conditions
← Back to the class: Viral vaccines
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Chapter 12: Influenza | Pink Book | CDC (Centers for Disease Control and Prevention, 2021); Lineamiento Técnico y Operativo de la Primera Jornada Nacional de Vacunación (Ministerio de Salud y Protección Social (Colombia), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.