Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

Mark Pritchard


DPhil Student in Clinical Medicine

  • Honorary specialty registrar in public health

I started my DPhil [PhD] in 2021, funded by the National Institute for Health and Care Research (NIHR) Health Protection Research Unit in Emerging and Zoonotic Infections. I am interested in how we can combine mathematical models with causal inference from observational data to generate the most robust evidence possible for decision makers. I am approaching this through the question of optimal timing of repeat vaccination against covid-19 for healthcare workers.

A simple compartmental model that allows for waning and boosting of immunity suggests a non-linear relationship between the prevalence of a pathogen and the frequency of re-infection. If our healthcare systems are operating in the 'plateau' region of this plot, where re-infections are relatively uncommon, then a decrease in the prevalence of the disease could lead to an apparently paradoxical increase in infections among healthcare workers.

Flow chart of a compartmental model that allows boosting and waning of immunity. Dashed red lines are proportional to the force of infection. Compartments represent the numbers of healthcare workers who are susceptible to infection (S), exposed to infection (E), infectious (I) and currently resistant to re-infection (R)

Predicted frequency of re-infection for differing forces of infection and different parameters of immune boosting (ε)

I am using simulations to explore the conditions in which this could be a significant concern for healthcare systems, healthcare workers and their patients. I am also looking at routinely collected data to explore whether it appears likely that such conditions exist in the ongoing covid-19 pandemic.


My route to public health included jobs with the NHS Breast Cancer Screening Programme and the Cancer Research UK Clinical Trials Unit at the University of Birmingham. I then decided that a career in medicine was the route I needed to follow to achieve my goals, and I was fortunate to gain a place on a graduate-entry medicine course. I followed this with an academic foundation programme at the Royal Stoke University Hospital and further hospital jobs in acute medicine, intensive care and infectious diseases. I also spent three months on a conservation and research expedition in Madagascar. 

I joined the Thames Valley public health training programme in 2017. When the covid-19 pandemic started I had the opportunity to spend nine months with the International Severe Acute Respiratory and Emerging Infection Consortium as part of their global response. My interest in medical research, which had never waned, was further boosted and I applied to start a DPhil the following year.