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Risk of convulsions in children after monovalent H1N1 (2009) and trivalent influenza vaccines: a database study

Julia Stowe1, Nick Andrews, Phil Bryan

  • 1Immunisation, Hepatitis and Blood Safety Department, Health Protection Agency, London, United Kingdom. julia.stowe@hpa.org.uk

Vaccine
|October 25, 2011
PubMed

Insights

This study found no increased risk of convulsions in children after receiving the monovalent H1N1 (2009) pandemic influenza vaccine or seasonal trivalent influenza vaccine (TIV). A potential, but not statistically significant, elevated risk was observed after the second dose of the H1N1 vaccine.

Area of Science:

  • Pediatric infectious diseases
  • Vaccine safety and reactogenicity
  • Epidemiology

Background:

  • The 2009/10 H1N1 pandemic influenza vaccine, adjuvanted with ASO3, was highly immunogenic but associated with fever in children.
  • Limited comparative data exists on the reactogenicity of seasonal trivalent influenza vaccines (TIV).
  • Investigating convulsion risk post-vaccination is crucial for understanding vaccine safety in pediatric populations.

Purpose of the Study:

  • To assess the risk of convulsions in children following vaccination with the monovalent H1N1 (2009) pandemic influenza vaccine.
  • To evaluate the risk of convulsions after receiving seasonal trivalent influenza vaccines (TIV).
  • To compare the reactogenicity of these influenza vaccines in a real-world setting.

Main Methods:

  • Utilized the General Practice Research Database (GPRD) employing a self-controlled case-series method.
  • Identified 2366 children under 10 years with recorded convulsions and influenza vaccination history (May 2000-April 2010).
  • Analyzed 3846 convulsion episodes in relation to monovalent H1N1 and TIV vaccination dates.

Main Results:

  • No increased incidence rate ratio (IRR) for convulsions was observed in the week following monovalent H1N1 or first-dose TIV vaccination.
  • A potential signal of elevated risk (IRR 3.48) was noted for days 1-3 post the second dose of monovalent H1N1 vaccine, consistent with increased fever.
  • No evidence of increased convulsion risk was found for TIV over 10 years or for a single dose of the ASO3-adjuvanted H1N1 vaccine.

Conclusions:

  • The study provides no evidence of an increased risk of convulsions associated with TIV vaccination over a decade.
  • A single dose of the ASO3-adjuvanted monovalent H1N1 vaccine in 2009/10 did not show an increased risk of convulsions.
  • Further investigation into potential risks after multiple doses of the H1N1 vaccine may be warranted, considering fever findings.

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