New Study Shows Efficacy of Typhoid Conjugate Vaccine

Typhoid fever is caused by Salmonella Typhi, a highly invasive bacterium that infects humans, usually after ingesting contaminated food or water. Low-income countries continue to be burned by typhoid cases, particularly in areas of Asia and Africa that have inadequate access to clean water and sanitation.

Typhoid vaccines have been developed in the past but have limitations.

To exacerbate the problem, the rise of antibiotic resistance has reduced the effectiveness of existing treatments. Multi-drug-resistant typhoid strains are increasing in Asia, highlighting the need for effective typhoid vaccination in endemic areas to protect public health.

Malawi, a small country in Southern Africa, had 32,747 typhoid cases in 2017, a rate of 191 cases per 100,000 people. Approximately 61% of these cases occurred in children under 15 years old. Additionally, there were 435 typhoid deaths that year, with 66% of them occurring in children under 15.

A study published January 25th in The Lancet revealed the efficacy of a single-dose typhoid conjugate vaccine. The four-year, phase 3 trial assessed the vaccine's effectiveness in preventing typhoid fever in Malawian children. The Bill & Melinda Gates Foundation funded the study.

“The newly published study supports the long-lasting impacts of a single shot of TCV, even in the youngest children, and offers hope of preventing typhoid in the most vulnerable children,” Kathleen Neuzil, MD, MPH, professor of vaccinology at the University of Maryland School of Medicine and director for the Center for Vaccine Development, and senior author of the current study, said in a press release.

The study enrolled over 28,000 children aged 6 months to 12 years and randomly assigned them to receive either the typhoid conjugate vaccine (Vi-TT) or a meningococcal A conjugate vaccine (MenA) as a control. The researchers then monitored the participants for typhoid fever cases over the course of the trial. The primary outcome measure was blood culture-confirmed typhoid cases.

The results showed that the typhoid conjugate vaccine was highly effective in preventing typhoid fever. The vaccine showed an overall efficacy of 80% in the per-protocol analysis, with a risk reduction of 6.1 typhoid infections per 1000 vaccinated children. Out of the 13,945 blood culture-confirmed typhoid cases in the Vi-TT arm, there were only 22 cases, compared to 109 cases in the MenA arm. The vaccine's efficacy remained consistent across different age groups.

“Prior typhoid vaccines have required multiple doses and/or did not work well in young children,” Neuzil stated in an email to MHE.

“We demonstrated that a single dose typhoid conjugate vaccine is effective for all ages of children and for more than four years, rendering it feasible for use on a large scale in low resource countries,” she stated.

The Malawi government started rolling out the vaccine to children under 15 in May 2023. Moving forward, all children in Malawi will get the TCV at nine months of age as part of routine immunization.