How many people in Switzerland have already had Covid-19? This is a question a network of Swiss scientists is trying to answer.
In Switzerland, RT-PCR (reverse transcription polymerase chain reaction) swab testing for Covid-19 has generally been reserved for only the sickest patients. This means many of those infected are missing from the official case number, leaving the true number of infections open to speculation.
A national study, dubbed Corona Immunitas, conducted by the Swiss School of Public Health (SSPH+), a national network of 12 universities, aims to answer this question and investigate the extent of immunity in people infected with the disease.
On 23 April 2020, Switzerland’s Federal Office of Public Health (FOPH) announced it would support the research, which is based on a proposal by Professor Milo Puhan, Head of the Institute of Epidemiology at the University of Zurich.
The study will also look at whether the body’s response to infection creates immunity from renewed infection, and if so, how long this immunity lasts. This will involve testing and examining around 25,000 people from the general population and specific professional groups at regular intervals until October 2020. A blood test will determine whether the person has had the virus: the presence of antibodies in the blood will indicate that they have. The first tests started in Geneva on 6 April 2020.
The FOPH is helping to fund the study and is providing expertise. The findings will provide valuable information which will help the cantons and the federal government better decide how to respond to the pandemic. It could also guide decisions related to an eventual vaccination programme.
A key challenge with serological (blood based) antibody testing is test accuracy. False positives, when the test detects Covid-19 antibodies but none are actually present, are a known problem with some antibody tests. In some cases tests confuse antibodies for other coronaviruses with Covid-19 antibodies. So finding and using a reliable test is critical to the success of these studies.
Men and women of all age groups and children from 5 years of age will be randomly selected across Switzerland for the test. A similar study in Santa Clara in the US was criticised for selecting candidates via Facebook adverts. Some suspect that people who thought they had had the virus but who had failed to get a RT-PCR swab test, flocked to get a free antibody test, skewing the sample towards a highly infected group. It is also possible they shared the advert with friends in a similar situation, skewing the sample further.
Corona Immunitas website (in English)