Funder: OUCRU

Principal Investigator: Marc Choisy (OUCRU)

Locations: OUCRU-HCMC

Timeline: started in July 2021

Aims:

The number one goal of COVID-19 vaccines is to reduce as much as possible the risk of severe forms of COVID-19, and this objective is fulfilled by all the vaccines currently used. However, we also know that vaccines do not 100% prevent infections, and, in case of infection, they do not 100% prevent transmission either. There is more and more data that is published on the detailed within-host viral and immunological dynamics following infection or vaccination. This allows us to estimate, almost day by day, the degrees of infectiousness after infection and protection after vaccination and recovery. The aim is to develop a mathematical model based on these very detailed data, and that would account for both the within-host and between-host dynamics of the virus. This model will then be used in order to look for the optimal timing of the second dose of a vaccine. From an immunological point of view, the later the second dose is administrated, the higher its efficiency. However, from an epidemiological point of view, the later the second dose is given, the more time is given to the virus to spread in the population. We will use the model to find the optimal timing that trades off these within- and between-host processes.

Importance:

Vaccination is the only way to return to normal life. The better the vaccination campaign is tuned, the sooner the return to normal life will be, and the more lives can be saved. Furthermore, there are several vaccines that are now in use, and the use of one type over another one depends essentially on the availability of each vaccine. It becomes important too to understand what are the effects of mixed vaccinations that include a first dose of one type and a second dose of another type. Finally, it has also been proposed that giving half a dose to twice as many people could be an efficient strategy at the epidemiological level.

Objectives:

• Is it better to vaccinate twice as many people with one dose or twice as fewer people with two doses. The answer likely depends on the types of vaccine and the exact epidemiological situation.
• Same questions with half a dose.
• What is the optimal timing of the second dose? The answer likely depends on the types of vaccine and the exact epidemiological situation.