Over 93% of the population of Geneva has developed antibodies against SARS-CoV-2
The fourth phase of our seroprevalence study, conducted in May and June 2022 in collaboration with the University of Geneva and EPFL, shows that almost all Genevans (93.8%) have antibodies against SARS-CoV-2. Nearly three quarters of them acquired them following an infection. Eight out of ten people have defences against the Alpha and Delta variants, but fewer than one in two (46.7%) have antibodies against the BA.4/BA.5 Omicron sub-variants. The latter are particularly low in children under the age of 12. The study has already been pre-published in English.
Twenty-nine months after the start of the COVID-19 pandemic, virtually the entire population has developed antibodies against SARS-CoV-2 following exposure to different variants and/or vaccination. The study shows that the overall seroprevalence of antibodies against SARS-CoV-2 is now 93.8%. In people aged 75 and over, seroprevalence linked to infection and/or vaccination rises to 96.7%. There was no difference between men and women. Three quarters (72.4%) of the population acquired the virus through infection, an increase of more than 42% in one year.
Our previous study published in June-July 2021 reported antibodies in two-thirds of the population. Half of them (29.9% of the population) had acquired them by infection. The introduction of vaccination in December 2020 and its extension to 12-15 year-olds from June 2021 and to 5-11 year-olds from January 2022, as well as the Delta (autumn-winter 2021/2022) and Omicron (winter-spring 2022) waves, have altered the population's immune landscape.
- Reduced immunity to Omicron
In vitro analyses conducted at the Ecole Polytechnique Fédérale de Lausanne (EPFL) are being used to test the extent to which these antibodies neutralise the different variants of the virus, in principle limiting the risk of new infections by them. Eight out of ten people (79.5%) have antibodies that neutralise Alpha, while less than half (46.7%) have antibodies that neutralise Omicron sub-variants BA.4 and BA.5.
- Children potentially less protected against Omicron
Over 90% of children aged 6 to 11 and over 75% of children aged 0 to 5 acquired antibodies following infection. However, in children under the age of 12, these antibodies appear to be significantly less neutralising than in older people, particularly against Omicron sub-variants. " According to our models, this can be explained in part by a lower vaccination rate among minors than among adults ", explains Pre Silvia Stringhini, epidemiologist in charge of the Population Epidemiology Unit at the HUG and assistant professor at the UNIGE Faculty of Medicine.
- Significant effect of booster vaccination
The study shows that vaccination, and in particular the booster dose, makes a major contribution to the neutralising power of antibodies against the Alpha and Delta variants. In fact, immunity against these variants is over 90% in people who have received booster doses, whereas it falls to 60% in uninfected people who have received only two doses. As far as the Omicron sub-variants are concerned, it is the combination of booster vaccination and recent infection that provides the best protection.
- Studies essential for public health programmes
Precise, up-to-date knowledge of the population's immunity and its ability to resist the different variants is invaluable for making appropriate public health decisions as the different waves occur. With this in mind, the team of researchers co-ordinated by the HUG and the UNIGE estimated the seroprevalence and neutralisation capacity of the different variants in Geneva and Switzerland, after Omicron became dominant in Geneva.
Prof. Idris Guessous, Head of the Department of Primary Care Medicine at the HUG and Associate Professor at the UNIGE Faculty of Medicine, who was responsible for the study, explains that " the results of this study suggest that the development of vaccines specifically targeting Omicron variants would be useful in preventing the spread of infections and their health and economic consequences ".
- More than 2,500 Genevans took part in the study
The serological study was carried out between 29 April and 9 June 2022 among 2,521 people of all ages in Geneva. The group was made up of 55.2% women, 21.4% under the age of 18 and 14.2% aged 65 or over. The presence of antibodies against SARS-CoV-2 was assessed using commercial immunoassays targeting the Spike protein or the nucleocapsid protein. The neutralisation capacity of the antibodies against different variants was assessed using a test developed by the teams of Professors Didier Trono at EPFL and Giuseppe Pantaleo at CHUV.
The study is being funded by the Fondation privée des HUG.
For more information about this study, visit our page Research
