Research in children from Bangladesh confirms the long-term effectiveness of a vaccine against typhoid fever in older children

A recently published study in “The Lancet” has confirmed that a single dose of typhoid conjugate vaccine (TCV) provides strong protection for older children against typhoid fever, although its effectiveness decreases over time, especially in younger children.

The TyVOID study, conducted in Bangladesh, tracked the vaccine’s effectiveness over five years, reports Oxford Vaccine Group.

According to the research report published today (October 11), the TCV provided a high level of protection between 80% and 96% for all children within two years after vaccination. However, the vaccine’s effectiveness decreased over time, especially in children vaccinated at a younger age.

Between three and five years after vaccination, the data showed a significant increase in the incidence of typhoid among children vaccinated in 2018/2019 and among children vaccinated in 2021. Despite this, children vaccinated at two years of age or older remained well protected, with effectiveness rates ranging from 59% to 85%.

In contrast, a clear decrease in protection was observed in children vaccinated under two years of age, suggesting that a booster dose may be necessary to maintain immunity in this age group.

“Typhoid is a serious and life-threatening disease, especially for children in low- and middle-income countries,” said Xinxue Liu, Associate Professor of Medical Statistics and Epidemiology at the Oxford Vaccine Group, and one of the senior authors of the study. .

“This study underlines the importance of TCV in reducing typhoid cases and provides valuable information for policymakers on the long-term protection provided by the vaccine.”

Dr. Firdausi Qadri, senior scientist at icddr,b and first author of the study, explained: “This research extends the original TyVAC study, following the population for a further two and a half years after the 2021 unmasking. Our findings suggest a decrease in the number of antibodies. levels across different age groups and indicate that a booster dose around school age for those vaccinated under the age of two could support protection throughout the school years.”

The WHO currently recommends a single dose of TCV for children aged six months and older. However, the study’s findings raise questions about the long-term protection of a single dose, especially for younger children, said Professor Sir Andrew Pollard, director of the Oxford Vaccine Group.

“Whether a single dose of TCV provides long-term protection remains a priority for research, and it is essential to continue studies to inform future policy decisions.”

Typhoid fever continues to pose a significant health burden, especially in low-income countries where access to clean water and sanitation is limited. The disease is responsible for an estimated 7 million cases and 93,000 deaths annually worldwide, with children under five particularly at risk.

Bangladesh ranked fourth in under-5 mortality due to typhoid in 2019.

The spread of drug-resistant forms of typhoid has increased the threat of the disease, reducing treatment options and making preventive measures such as vaccination all the more important.

The first TCV, developed by Bharat Biotech International, received prequalification from WHO in 2017, and in 2018 WHO recommended its use as an important tool for typhoid prevention.

With TCV set to be rolled out in vaccination campaigns across Bangladesh in 2025, the TyVOID study, funded by the Bill and Melinda Gates Foundation, highlighted the need for continued research to monitor the long-term effectiveness of the vaccine and its impact on antibiotic resistance. These data will be essential for WHO as it continues to update its guidelines for the prevention and control of typhoid fever.