Typhoid: Study confirms typhoid conjugate vaccine is safe and immunogenic in children under age 2

A new study conducted by IVI in collaboration with SK bioscience shows that single-dose and two-dose regimens of Vi-DT typhoid conjugate vaccine (TCV) are safe and immunogenic in children six to 23 months of age, a group with high rates of typhoid fever in resource-limited settings. The findings from this study, newly published online in EClinicalMedicine, describe the successful completion and analysis of a Phase II clinical trial of Vi-DT six months after vaccination.

The World Health Organization (WHO) recommends TCVs for use in endemic settings with Gavi, the Vaccine Alliance providing the vaccines to eligible countries. However, with only one TCV pre-qualified by the WHO, demand currently exceeds supply. This study is a critical step toward gaining licensure and WHO-prequalification of an additional TCV to increase the global stockpile.

"Our findings show that a single dose of conjugated Vi-DT vaccine is safe and provides anti-Vi seroconversion rates similar to the two-dose regimen in children between six months and two years of age," said Dr. Birkneh Tilahun Tadesse, a Research Scientist at the International Vaccine Institute (IVI), which conducted the study at the Research Institute for Tropical Medicine in Manila, the Philippines.

"This is an important advance, considering the significant burden of disease in infants and young children, and our goal remains developing a safe, single-dose vaccine with long-lasting immunogenicity to protect more children against typhoid fever," said Dr. Sushant Sahastrabuddhe, Director of the Typhoid Program at IVI.

Key facts about typhoid:

• Typhoid fever is a life-threatening infection caused by the bacterium Salmonella Typhi. It is usually spread through contaminated food or water.

• An estimated 11–20 million people get sick from typhoid and between 128 000 and 161 000 people die from it every year.

• Symptoms include prolonged fever, fatigue, headache, nausea, abdominal pain, and constipation or diarrhoea. Some patients may have a rash. Severe cases may lead to serious complications or even death.

• Typhoid fever can be treated with antibiotics although increasing resistance to different types of antibiotics is making treatment more complicated.

• Two vaccines have been used for many years to prevent typhoid. A new typhoid conjugate vaccine with longer lasting immunity was prequalified by WHO in December 2017.