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5th February 2024 (9 Topics)

India-made typhoid vaccine efficacy lasts for four years

Context

The efficacy of the conjugated typhoid vaccine at the end of 4.3 years of median follow-up was 70·6% for children aged nine months to two years; the efficacy was over 79% in children above two years.

Introduction

In a groundbreaking phase-3 trial conducted in Malawi, Africa, Bharat Biotech's conjugate typhoid toxoid vaccine, Typbar, demonstrates remarkable long-term efficacy in children aged nine months to 12 years.

Trial Details:

Location: Malawi, Africa - a typhoid fever-endemic setting.

Duration: February to September 2018. Participants: 28,130 healthy children randomly assigned to receive Typbar or meningococcal A conjugate vaccine.

Blindness: Double-blind trial - researchers and participants unaware of vaccine assignments.

Efficacy Results:

  • Overall Efficacy: Lasts for at least four years.
  • Age-specific Efficacy: Varied from 70.6% (nine months to two years) to 79.3% (five to 12 years).
  • Incidence: 24 cases of typhoid fever in the Typbar group vs. 110 in the control group during the follow-up.

Durability of Protection:

  • Significance: Particularly crucial for children under two years.
  • Follow-up: Longer follow-up identifies increased cases prevented by the original single-dose vaccine.

Risk Reduction and Cumulative Efficacy:

  • Risk Reduction: 6.1 typhoid infections per 1,000 vaccinated children.
  • Number Needed to Vaccinate: 163 to prevent one case.
  • Cumulative Vaccine Efficacy: 83.4% after one year, declining modestly to 78.3% after 4.61 years.

Comparison with Earlier Trials:

  • Consistency: Long-term trial aligns with earlier high efficacy findings in shorter-term trials.
  • Earlier Trials: Showed efficacy ranging from 79% to 85% over 18-24 months.

Implications and Recommendations:

  • Cost-effectiveness: Study supports the high estimated cost-effectiveness of conjugate typhoid vaccines.
  • Second Dose Consideration: Mathematical models suggest potential typhoid rebound in children aged 5-15; longer studies and booster dose investigations are recommended.

Way forward: The Lancet-published trial marks a significant stride in understanding the lasting efficacy of Bharat Biotech's Typbar in typhoid-endemic regions, offering hope for enhanced preventive measures against a disease with a significant global burden.

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