Immunity acquired by a minority active fraction of the population could explain COVID-19 spread in Greater Buenos Aires (June?November 2020)

FABRICIUS, GABRIEL; BORZI, R. A.; CAMINOS, JOSÉ; GRIGERA, TOMAS S.

EPIDEMIOLOGY AND INFECTION.

CAMBRIDGE UNIV PRESS

Lugar: Cambridge; Año: 2022 vol. 150 p. 84 - 84

0950-2688

The coronavirus disease 2019 (COVID-19) pandemic had an uneven development in differentcountries. In Argentina, the pandemic began in March 2020 and, during the first 3 months,the vast majority of cases were concentrated in a densely populated region that includes thecity of Buenos Aires (country capital) and the Greater Buenos Aires (GBA) area that sur-rounds it. This work focuses on the spread of COVID-19 between June and November2020 in GBA. Within this period of time there was no vaccine, basically only the early wildstrain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was present, andthe official restriction and distancing measures in this region remained more or less constant.Under these particular conditions, the incidences show a sharp rise from June 2020 and beginto decrease towards the end of August until the end of November 2020. In this work we study,through mathematical modelling and available epidemiological information, the spread ofCOVID-19 in this region and period of time. We show that a coherent explanation of the evo-lution of incidences can be obtained assuming that only a minority fraction of the populationgot involved in the spread process, so that the incidences decreased as this group of people wasbecoming immune. The observed evolution of the incidences could then be a consequence atthe population level of lasting immunity conferred by SARS-CoV-2.