Preceding anti-spike IgG levels predicted risk and severity of COVID-19 during the Omicron-dominant wave in Santa Fe city, Argentina

Abstract

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 arrival of Omicron allowed to assess the acquired humoral defences preceding the wave and to conduct a longitudinal study to provide individual-level real-world data linking antibody levels and protection against COVID-19 during the wave. A very large proportion of 1455 sampled individuals had immunological memory against COVID-19 at the arrival of Omicron (almost 90%), and about half (48.9%) had high anti-spike immunoglobulin G levels (>200 UI/ml). However, the antibody titres varied greatly among the participants, and such variability depended mainly on the vaccine platform received, on having had COVID-19 previously and on the number of days elapsed since last antigen exposure (vaccine shot or natural infection). A follow-up of 514 participants provided real-world evidence of antibody-mediated protection against COVID-19 during a period of high risk of exposure to an immune-escaping highly transmissible variant. Pre-wave antibody titres were strongly negatively associated with COVID-19 incidence and severity of symptoms during the wave. Also, receiving a vaccine shot during the follow-up period reduced the COVID-19 risk drastically (15-fold). These results highlight the importance of maintaining high defences through vaccination at times of high risk of exposure to immune-escaping variants.

Keywords: Antibody titre; SARS-CoV-2; disease severity; humoral defences; infection risk; longitudinal study; pre-exposure.

Fig. 1.

Temporal distribution of the confirmed cases of COVID-19 in Santa Fe city (official records of the Ministry of Health of Santa Fe province).

Fig. 2.

Levels of antibodies (IgG) against SARS-CoV-2 by the number of vaccine doses and prior COVID-19 diagnosis.

Fig. 3.

Levels of antibodies (IgG) against SARS-CoV-2 by vaccine scheme and prior COVID-19 diagnosis. Sph, Sinopharm; AZ, Astra Zeneca; Spk, Sputnik V; Mod, Moderna; Pfi, Pfizer/BioNTech.

Fig. 4.

Predicted probability of COVID-19 during the Omicron-dominant wave depending on the levels of antibodies (IgG) against SARS-CoV-2 and the administration of a vaccine dose during the wave. For the simulation contact with cases was set at 1.

Fig. 5.

Levels of antibodies (IgG) against SARS-CoV-2 at the onset of the Omicron-dominant wave by the severity of the symptoms when they became infected during the wave.