Imported Infections Versus Herd Immunity Gaps; A Didactic Demonstration of Compartment Models Through the Example of a Minor Measles Outbreak in Hungary

Katalin Böröcz*; Ákos Markovics; Zsuzsanna Csizmadia; Joseph Najbauer; Timea Berki; Péter Németh

doi:10.26332/seemedj.v5i1.199

Katalin Böröcz* Department of Immunology and Biotechnology, Clinical Centre, University of Pécs Medical School, Pécs, Hungary
Ákos Markovics Department of General and Physical Chemistry , Faculty of Natural Sciences, University of Pécs, Pécs, Hungary
Zsuzsanna Csizmadia Department of Immunology and Biotechnology, Clinical Centre, University of Pécs Medical School, Pécs, Hungary
Joseph Najbauer Department of Immunology and Biotechnology, Clinical Centre, University of Pécs Medical School, Pécs, Hungary
Timea Berki Department of Immunology and Biotechnology, Clinical Centre, University of Pécs Medical School, Pécs, Hungary
Péter Németh Department of Immunology and Biotechnology, Clinical Centre, University of Pécs Medical School, Pécs, Hungary

DOI: https://doi.org/10.26332/seemedj.v5i1.199

Abstract

Introduction: In Hungary, where MMR vaccine coverage is 99%, in 2017, a minor measles epidemic started from imported cases due to two major factors – latent susceptible cohorts among the domestic population and the vicinity of measles-endemic countries. Suspended immunization activities due to the COVID-19 surge are an ominous precursor to a measles resurgence. This epidemiological demonstration is aimed at promoting a better public understanding of epidemiological data.

Materials and Methods: Our previous MMR sero-epidemiological measurements (N of total measles cases = 3919, N of mumps cases = 2132, and N of rubella cases = 2132) were analyzed using open-source epidemiological data (ANTSZ) of a small-scale measles epidemic outbreak (2017, Hungary). A simplified SEIR model was applied in the analysis.

Results: In case of measles, due to a cluster-specific inadequacy of IgG levels, the cumulative seropositivity ratios (measles = 89.97%) failed to reach the herd immunity threshold (HIT Measles = 92–95%). Despite the fact that 90% of overall vaccination coverage is just slightly below the HIT, unprotected individuals may pose an elevated epidemiological risk. According to the SEIR model, ≥74% of susceptible individuals are expected to get infected. Estimations based on the input data of a local epidemic may suggest an even lower effective coverage rate (80%) in certain clusters of the population.

Conclusion: Serological survey-based, historical and model-computed results are in agreement. A practical demonstration of epidemiological events of the past and present may promote a higher awareness of infectious diseases. Because of the high R0 value of measles, continuous large-scale monitoring of humoral immunity levels is important.