Controlled field trial of a high-dose oral killed typhoid vaccine in India

Area of Science:

• Immunology
• Infectious Diseases
• Vaccinology

Background:

• Typhoid fever remains a significant public health concern globally, particularly in regions with poor sanitation.
• Effective vaccines are crucial for controlling typhoid fever outbreaks and reducing disease burden.

Purpose of the Study:

• To assess the efficacy of a modified oral typhoid vaccine (Salmonella typhi, TY 2 strain) in preventing typhoid fever.
• To evaluate vaccine effectiveness in a controlled field trial among schoolchildren.

Main Methods:

• A controlled field trial was conducted involving schoolchildren aged 6-17 years.
• Participants were randomized to receive either the oral typhoid vaccine (400 x 10(9) killed organisms/capsule) or a placebo.
• Follow-up duration was 6-8 months, with typhoid fever cases monitored in both groups.

Main Results:

• There were 66 cases of typhoid fever in the vaccine group (n=7312) and 54 cases in the placebo group (n=7292).
• The observed difference in typhoid fever incidence between the vaccine and placebo groups was not statistically significant.
• This indicates a lack of protective effect from the oral typhoid vaccine at the tested dosage.

Conclusions:

• The oral typhoid vaccine, utilizing the Salmonella typhi TY 2 strain at the tested dosage, did not demonstrate efficacy in preventing typhoid fever in schoolchildren.
• These findings are consistent with previous trials suggesting limited protection from oral typhoid vaccines at current dosages.
• Further research into alternative vaccine formulations or dosages may be warranted for effective typhoid fever prevention.