The SARS-CoV-2 Omicron variant has increased infectivity and immune escape compared with previous variants, and caused the surge of massive COVID-19 waves globally. Despite a vast majority (~90%) of the population of Santa Fe city, Argentina, had been vaccinated and/or had been infected by SARS-CoV-2 when Omicron emerged, the epidemic wave that followed its arrival was by far the largest one experienced in the city. A serosurvey conducted prior to the
The SARS-CoV-2 variant of concern Omicron has increased infectivity and immune escape compared with previous variants. Despite a vast majority (∼90%) of the population of Santa Fe city (Argentina) had been vaccinated and/or had been infected by SARS-CoV-2 prior to the arrival of Omicron, the epidemic wave caused by this variant was by far the largest one experienced in the city. Nevertheless, the severity was much lower than that of previous waves. A serosurvey conducted within a month prior to the arrival of Omicron allowed to assess the humoural defences preceding the wave and to evaluate their consequences on infection risk and severity. Santa Fe is a city of 430000 inhabitants, the survey was conducted on 1452 citizens, 514 of which were followed-up until March 2022. A high proportion of the sampled individuals had immunological memory against COVID-19 at the arrival of Omicron (almost 90%), many of whom had high antibody levels. The anti-spike IgG titres were strongly associated with the number of vaccine shots and the vaccine platform received, and also depended markedly on prior COVID-19 diagnosis and the days elapsed since last antigen exposure (vaccine shot or natural infection). In turn, various analytical approaches consistently showed that preceding antibody titres were strongly correlated with COVID-19 incidence and severity of symptoms during the Omicron-dominant wave. Also, receiving a vaccine shot during the wave reduced the COVID-19 risk drastically (15-fold). Here we present real world data showing that COVID-19 incidence and severity during the Omicron-dominant wave was lowest in individuals with high antibody levels, which highlight the importance of maintaining high defences through vaccination in the presence of immune-escaping variants.
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