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Study finds high level of hybrid immunity in Swiss general population

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A recent study in the Swiss general population assessed 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.

Study: Development of hybrid immunity during a period of high incidence of infections with Omicron subvariants: a population-based, multi-regional cohort study. Image Credit: Tang Yan Song/Shutterstock

Background

SARS-CoV-2, the pathogen responsible for the coronavirus disease 2019 (COVID-19) pandemic, has so far caused more than 625 million infections and 6.5 million deaths worldwide. Although the rapid deployment of vaccines has significantly controlled the pandemic trajectory, continued surveillance of anti-SARS-CoV-2 immunity in the general global population is still needed.

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

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

study design

This study is 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 major regions of Switzerland. Seroprevalence was measured from March to July 2022.

Blood samples taken from the participants were analyzed for anti-spike and anti-nucleocapsid IgG antibodies. Additionally, neutralizing antibody levels against wild-type 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 participants. A history of SARS-CoV-2 infection was determined by anti-nucleocapsid seroprevalence, a positive test report for the virus, or the presence of anti-spike antibodies in the absence of vaccination.

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

Important observations

The study involved a total of 2553 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 at 98% at the end of the study period (July 2022). The proportion of participants with anti-spike IgG antibodies was over 90%. Regarding neutralizing titers, approximately 94%, 90%, and 84% of participants showed seropositivity against wild-type virus, delta variant, and omicron variant, respectively.

Over the 4-month study period, anti-spike antibody levels remained generally stable in Switzerland, while anti-nucleocapsid antibody levels showed a rapid decline. A significant induction of susceptibility to infection by omicron was also observed in all study regions in spring 2022.

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

The highest level of neutralizing efficacy against delta and omicron was observed in participants with hybrid immunity. This effectiveness was lowest in participants with previous exposure to the virus only.

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

Significance of the study

The study highlights a high level of anti-SARS-CoV-2 immunity in the Swiss general population in 2022. Approximately 51% of study participants have hybrid immunity, characterized by high levels of neutralization capability 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.