Frederico Moreira

Frederico is currently a student of the Master in Biostatistics from the Faculty of Sciences at the University of Lisbon, Portugal. He joined the group in February 1st 2021 to conduct his MSc project on herpesvirus reactivation in Astronauts under the supervision of Nuno Sepúlveda and Marília Antunes.

Title of Project:

Longitudinal analysis of viral shedding in astronauts before, during, and after a mission to the International Space Station


Astronauts live under considerably challenging conditions in space, such as loss of gravity, lack of exposure to natural light, confinement, among others. These stressful conditions like others occurring on earth provide the perfect environment for the reactivation of latent infections by common herpesviruses (e.g., Epstein-Barr, Varicella-Zoster, and Cytomegalovirus). In turn, the reactivation of these viruses has been linked to many severe pathologies, such as the Chronic Fatigue Syndrome, cancer, and arteriosclerosis. To understand the conditions by which these viruses could be reactivated, a recent study analysed data from 23 astronauts on viral shedding before, during, and after a long-duration mission to the International Space Station (Mehta et al, 2017).


In the original publication, the data set was basically analysed by estimating prevalence of viral shedding at different timepoints. This project aims to extend this analysis by using longitudinal zero-inflated Poisson and Negative-Binomial models (Molenberghs & Verbeke, 2005) together with different missing data imputation techniques, such as multiple imputation based on chained equations (Van Buuren & Groothuis-Oudshoorn, 2001) .

Summary of work plan:

Literature review on methodology and the research topic related to data

Study of methods to be applied to the data

Construction of the database

Preliminary univariate analysis of each virus at each time point

Longitudinal analysis of each virus over time

Joint longitudinal analysis of multiple viruses


Mehta SK, Ladenslager ML, Stowe RP, Crucian BE, Feiveson AH, Sams CF, Pierson DL (2017). Latent virus reactivation in astronauts on the International space station. Npj Microgravity 3:11.

Molenberghs, G., Verbeke, G. (2005). Models for Discrete Longitudinal Data, Springer, USA.

Van Buuren, S., Groothuis-Oudshoorn, K. (2011). mice: Multivariate Imputation by Chained Equations in R. Journal of Statistical Software, 45(3), 1-67.