Majority in Population Study is Not Exhibiting COVID-19 Antibodies

During the spring COVID-19 outbreak, an examination of Swiss people in Geneva shows only a small amount of the population with IgG antibodies.

The population of Geneva, Switzerland did not see a high prevalence of coronavirus 2019 (COVID-19) antibodies despite the virus having a high case load in the region in the spring of 2020. The canton of Geneva has nearly half a million people, and there were 5000 reported cases in less than 2.5 months.

Silvia Stringhini, PhD, Division of Primary Care, Geneva University led a group of investigators who performed the SEROCoV-POP study, an assessment of the seroprevalence of anti-SARS-CoV-2 IgG antibodies which consisted of former participants of the Bus Santé study and their household members.

The SEROCoV-POP study was published in The Lancet.

The Bus Santé study is a yearly representative stratified sample of 500 men and 500 women, ages 20-74, from the general population of Geneva. Each participant received 3 self-administered, standardized questionnaires covering risk factors for major lifestyle-dependent chronic diseases, sociodemographic characteristics, educational and occupational histories, and, for women, reproductive history.

Investigators planned to do 12 consecutive weekly serosurveys among randomly selected participants from the Bus Santé study, as well as household members aged 5 years and older. They tested each participant for anti-SARS-CoV-2-IgG antibodies and estimated seroprevalence using a Bayesian logistic regression model.

For the SEROCoV-POP study, they enrolled 1399 households. A total of 2766 participants had complete data and were included in their analysis.

The results represent the first 5 weeks of the study. In week 1, the investigators estimated a seroprevalence of 4.8%; then 8.5% in week 2; in week 3, it increased again to 10.9%; then decreased in week 4 to 6.6%; then landed at 10.8% in the final week.

Using the ELISA Antibody test, 219 of 2766 individuals tested positive for SARS-CoV-2 anti-S1 IgG antibodies thus representing only 7.9% of the total participants.

“After accounting for the time to seroconversion, we estimated that for every reported confirmed case, there were 11.6 infections in the community,” the investigators wrote.

Individuals aged 5—9 years (relative risk [RR], 0.32%; 95% CI, 0.11–0.63) and those older than 65 years (RR, 0.50%; 95% CI, 0.28–0.78) had a significantly lower risk of being seropositive than those aged 20–49 years.

Compared with the population of Geneva, the sampling of this study had the 50-64 age group overrepresented and an underrepresentation of participants who were older than 80.

“At what appears to be the tail end of the first wave of the pandemic in Switzerland, about one in ten people have developed detectable antibodies against SARS-CoV-2, despite the fact that it was one of the more heavily affected areas in Europe,” investigators investigators wrote. “Thus, assuming that the presence of the IgG antibodies measured in this study is, at least in the short term, associated with protection, these results highlight that the vast majority of the population is still immunologically naive to this new virus.”