Study reveals the increased level of hybrid immunity in the public Swiss population

A recent study covering the general Swiss population has evaluated the development of hybrid immunity during the pandemic wave dominated by the omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The study, currently available on the medRxiv* preprint server, finds high seropositivity against SARS-CoV-2 in the study population


SARS-CoV-2, the causative pathogen of the coronavirus disease 2019 (COVID-19) pandemic, has so far caused over 625 million infections and 6.5 million deaths worldwide. Although the rapid deployment of vaccines has considerably controlled the pandemic trajectory, continuous monitoring of anti-SARS-CoV-2 immunity in the general global population is still required.

The emergence of the highly infectious omicron variant has caused a sharp increase in breakthrough cases among fully vaccinated individuals. This has led to a significant increase in neutralizing seroprevalence in the general global population. Therefore, it is generally considered that the immunity induced by both infection and vaccination, i.e., hybrid immunity, provides more robust protection against severe disease than that induced by infection or vaccination alone.

In the current study, scientists have assessed the seroprevalence against SARS-CoV-2 in the general Swiss population during the omicron-dominated pandemic wave.

Study design

This study is a part of the Corona Immunitas research program in Switzerland.

The study was conducted on more than 2,500 individuals from the general population residing in three main regions in Switzerland. The seroprevalence was measured during March – July 2022.

Blood samples collected from the participants were analyzed for anti-spike and anti-nucleocapsid IgG antibodies. In addition, the levels of neutralizing antibodies against wildtype SARS-CoV-2 and its delta and omicron variants were also determined (functional immunity).

To determine the source of anti-SARS-CoV-2 immunity, self-reported vaccination status was obtained from the participants. A history of SARS-CoV-2 infection was determined by anti-nucleocapsid seroprevalence, a virus-positive test report, or the presence of anti-spike antibodies in the absence of vaccination.

Participants were categorized into four groups based on their immune status: immunity-naïve, only vaccine-induced immunity, only infection-induced immunity, and hybrid immunity (immunity induced by both infection and vaccination).

Important observations

The study involved a total of 2,553 participants from three main regions of Switzerland. Most of them had received at least one dose of COVID-19 vaccines, and about 50% reported recent exposure to SARS-CoV-2.

The seroprevalence was estimated to be 98% by the end of the study period (July 2022). The proportion of participants with anti-spike IgG antibodies was more than 90%. Regarding neutralizing titers, about 94%, 90%, and 84% of participants showed seropositivity against wild-type virus, delta variant, and omicron variant, respectively.

During the 4-month study period, anti-spike antibody levels remained mostly stable in Switzerland, whereas anti-nucleocapsid antibody levels showed a rapid decline. A significant induction in susceptibility to omicron infection was also observed in all study regions in Spring 2022.

More than 2-times induction in anti-spike IgG antibody and neutralizing antibody levels was observed at the end of the study among vaccinated participants and those with hybrid immunity compared to the participants with a history of infection only.

The highest level of neutralizing efficacy against delta and omicron was observed in participants with hybrid immunity. This efficacy was lowest among participants with previous viral exposure only.

The proportion of participants with hybrid immunity increased from 35% to 50% by the end of the study period. This could be due to a sharp rise in omicron cases in Switzerland in Spring 2022.

Study significance

The study highlights a high level of anti-SARS-CoV-2 immunity in the general Swiss population in 2022. About 51% of study participants are with hybrid immunity, characterized by high neutralizing ability levels against delta and omicron variants.

Overall, the study indicates that SARS-CoV-2 has become endemic in Switzerland and that hybrid immunity induces more robust protection than vaccine- and infection-induced immunity alone.

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