Immunogenicity of the Vi-TCV typhoid conjugate vaccine and impacts on optimal vaccine policy

Typhoid fever is a serious illness caused by bacteria that can spread through contaminated food and water. It affects millions of people every year, especially in countries with limited access to clean water and sanitation. Vaccines, including the typhoid conjugate vaccine (TCV), have been developed to help prevent typhoid fever.

Our goal is to understand how long protection from the typhoid conjugate vaccine lasts, and how factors like geography and different levels of exposure to the bacteria might affect the best vaccination policies for countries around the world. Some places may have higher or lower risks of typhoid, and people may be exposed to the bacteria in different ways or amounts.

We have worked with the World Health Organization (WHO) to help improve recommendations for when and how to give the typhoid conjugate vaccine. We have found that the number of people who get typhoid fever can be reduced through vaccination, but the benefits of different vaccine schedules or extra booster shots can change depending on how quickly vaccine protection fades over time and the amount of typhoid risk in the community.

To better understand these issues, we will build and improve a model (a mathematical way to predict outcomes) that connects the amount of antibodies (protective proteins in the blood) a person develops after vaccination to how likely they are to be protected from typhoid fever. Our model will also take into account differences in how often people are exposed to typhoid bacteria in different locations.

We will use data that is already available to test and improve our model, but we will also look for more detailed real-world data to make our predictions more accurate. By doing this, we will be able to give better advice to public health experts and decision-makers about how to use the typhoid conjugate vaccine in different parts of the world, and whether changes in timing or extra doses are needed to protect people most effectively.