Association Between Vaccination Status and the Incidence of Breakthrough COVID-19 Infections Among University of Santo Tomas – Faculty of Medicine and Surgery Students: a Case-Control Study

Ryan Irvin M. Abustan, Joaquin V. Abundancia, Vincent Rhey L. Accad, Kimberly Mae H. Advincula, Jillian Elize R. Afable, Vanessa Joy A. Agraviador, Ida Marie Tabangay-Lim

Dec 2025 DOI 10.35460/2546-1621.2025-0110     Access   

Abstract

Introduction: With the introduction of COVID-19 vaccines, schools around the world have slowly started to reimplement on-site classes with guidelines to prevent outbreaks. The University of Santo Tomas has devised their own set of guidelines, including safety protocols, vaccinations and daily health declarations. These were monitored using the Thomasian Online Medical Services and Support (ThOMedSS).

Methodology: Through a case-control study design, the study aims to determine an association between the vaccination status of UST Faculty of Medicine and Surgery (UST-FMS) students and breakthrough COVID-19 infections in the first semester of the academic year 2022-2023, with population data acquired via records of students participating in face-to-face classes from the UST Health Service Office, and categorized based on breakthrough infections and vaccination status.

Statistical Analysis: Results were analyzed using Pearson’s chi-square test and Fisher’s exact test (p<0.05). Odds ratio was used to measure the effect of vaccination status on the incidence of breakthrough infections.

Conclusion: The study suggests that vaccination status did not have a statistically significant association (p = 0.3451) with breakthrough infections. The majority (99.94%) of students have received the complete primary COVID-19 vaccination series and only 6.61% of this population developed breakthrough COVID-19 infections, all occurring in those completely vaccinated. Breakthrough infections were 1.76 times more likely for those with booster shots than those without. The possible reason for this is the emergence of the Omicron variant. To improve the study, external exposures and individual behaviors must be considered as potential factors influencing infection rates.

Keywords: COVID-19, breakthrough infections, vaccination

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