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. 2023 Dec 25;52(6):1696-1707.
doi: 10.1093/ije/dyad098.

Development of hybrid immunity during a period of high incidence of Omicron infections

Anja Frei  1 , Marco Kaufmann  1 , Rebecca Amati  2 , Audrey Butty Dettwiler  3 , Viktor von Wyl  1   4 , Anna Maria Annoni  2 , Julia Vincentini  3 , Céline Pellaton  5 , Giuseppe Pantaleo  5 , Jan S Fehr  1 , Valérie D'Acremont  6 , Murielle Bochud  3 , Emiliano Albanese  2 , Milo A Puhan  1 ; Corona Immunitas Research Group
Collaborators, Affiliations

Development of hybrid immunity during a period of high incidence of Omicron infections

Anja Frei et al. Int J Epidemiol. .

Abstract

Background: Seroprevalence and the proportion of people with neutralizing activity (functional immunity) against SARS-CoV-2 variants were high in early 2022. In this prospective, population- based, multi-region cohort study, we assessed the development of functional and hybrid immunity (induced by vaccination and infection) in the general population during this period of high incidence of infections with Omicron variants.

Methods: We randomly selected and assessed individuals aged ≥16 years from the general population in southern (n = 739) and north-eastern (n = 964) Switzerland in March 2022. We assessed them again in June/July 2022, supplemented with a random sample from western (n = 850) Switzerland. We measured SARS-CoV-2 specific IgG antibodies and SARS-CoV-2 neutralizing antibodies against three variants (ancestral strain, Delta, Omicron).

Results: Seroprevalence remained stable from March 2022 (97.6%, n = 1894) to June/July 2022 (98.4%, n = 2553). In June/July, the percentage of individuals with neutralizing capacity against ancestral strain was 94.2%, against Delta 90.8% and against Omicron 84.9%, and 50.6% developed hybrid immunity. Individuals with hybrid immunity had highest median levels of anti-spike IgG antibodies titres [4518 World Health Organization units per millilitre (WHO U/mL)] compared with those with only vaccine- (4304 WHO U/mL) or infection- (269 WHO U/mL) induced immunity, and highest neutralization capacity against ancestral strain (hybrid: 99.8%, vaccinated: 98%, infected: 47.5%), Delta (hybrid: 99%, vaccinated: 92.2%, infected: 38.7%) and Omicron (hybrid: 96.4%, vaccinated: 79.5%, infected: 47.5%).

Conclusions: This first study on functional and hybrid immunity in the Swiss general population after Omicron waves showed that SARS-CoV-2 has become endemic. The high levels of antibodies and neutralization support the emerging recommendations of some countries where booster vaccinations are still strongly recommended for vulnerable persons but less so for the general population.

Keywords: COVID-19; SARS-CoV-2; cohort; functional immunity; hybrid immunity; infection; neutralization; population-based; seroprevalence; vaccination.

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Conflict of interest statement

None declared.

Figures

Figure 1.
Figure 1.
Trajectories of SARS-CoV-2 IgG antibodies and ACE2r-blocking (neutralizing activity) as measured by a virus-free assay, from March 2022 to June/July 2022. NuC, nucleocapsid; IgG, immunglobulin G. Seropositivity is defined based on the presence of anti-spike IgG antibodies according to the threshold of SenASTrIS test positivity with median fluorescence intensity (MFI) ≥6. Neutralization capacity based on virus-free assay with cut-off value of ≥50. Participants of Corona Immunitas from Ticino and Zurich, Switzerland (n = 1702)
Figure 2.
Figure 2.
Seroprevalence and hybrid immunity in Phases 5 and 6 of Corona Immunitas, Switzerland, in relation to the evolution of the pandemic, August 2021–August 2022. ICU, intensive care unit. The evolution of the pandemic is visualized by the number of laboratory-confirmed SARS-CoV-2 cases (in purple), hospitalizations (turquoise) and intensive care unit admissions (in yellow) in Switzerland between August 2021 and August 2022, retrieved from: [https://ourworldindata.org/coronavirus]. The time frame of Phases 5 (March 2022, n =1894) and 6 (June/July 2022, n = 2553) of Corona Immunitas, when the blood sampling and questionnaire assessments took place, are highlighted in light yellow. The results regarding seroprevalence and percentage of participants with hybrid immunity are visualized in dark and light blue bars, respectively
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References

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