The selection of a common test followed a stepwise procedure. It is one of the advantages of Corona Immunitas to learn from existing seroprevalence studies and the emergence of more and more evidence on the accuracy of serological tests and the nature of different tests (e.g. by having one or more targets and different antibodies). The testing group of Corona Immunitas first developed a set of 18 criteria (see online appendix) that refer to the nature of the test, results from validation studies and to logistics and cost of the test. They then opened a public call for companies and academic laboratories in Switzerland to apply for offering a common test for the Program and complete the openly accessible questionnaire with the 18 criteria. Members of the Corona Immunitas consortium then independently rated these applications, which was then compiled in a ranking at the end of May. Two commercial tests and one academic test ranked closely together.
When the executive committee was about to make the selection on the common test new evidence emerged on the accuracy of commercial tests. While specificity was high for most tests, which is crucial when seroprevalence is still low, there was evidence on limited sensitivity, which could be due to the small number and nature of targets of the tests (e.g. only S1 or N domain) or the kinetics of antibodies to certain targets. The academic tests have more targets, which is likely to capture more seropositive persons given the heterogenous immunological response of individuals. Most validation studies are likely to be substantially biased (e.g. spectrum bias, differential verification bias) because of their designs, as also pointed out by the recent Cochrane review. Biased estimates of accuracy make the adjustment of seroprevalence estimates for (imperfect) sensitivity and specificity uncertain.
The executive committee decided in June that more validation of commercial tests is needed before a test can be selected as the common test for the Program. At the same time, the two academic tests showed strong evidence about superior signal detection and accuracy compared to commercial tests and very low cross-reactivity. Evidence did not come from just case control accuracy studies but also from broad, population-based samples. Therefore, the executive committee invited the two academic laboratories to update information on their test and decided ultimately to use the Luminex test from CHUV, developed together with EPFL and the Swiss Vaccine Center, as the common test because of the trimeric (entire S) target, the strong signal detected in persons with and without symptoms at the time of infection, the availability of IgG and IgA, the possibility for quantitative interpretation, the availability of a neutralizing antibody test, evidence on superior performance in population-based samples in comparison with six commercial tests, availability of test material that is produced by EPFL and the possibility of use of this Luminex-based test in other laboratories in Switzerland.
We are happy to announce that the test from CHUV, together with EPFL and the Swiss Vaccine Center has been chosen as the common test for Corona Immunitas.
The paper describing the test and its properties can be found here.
