Focus mass testing: how to overcome low test accuracy ?
Mass testing can be key to managing the pandemic in 2021: avoid a third wave while vaccination is being deployed. However, the success of mass testing depends on several factors: the availability and the accuracy of the tests, and the prevalence of the virus. PCR tests are very accurate, but cannot be performed at a population-wide scale due to the limited laboratory capacity. On the other hand, antigen tests are widely available, but their lack of accuracy is problematic. If everyone is tested once, the vast majority of those who are tested positive are in fact virus free, which is problematic in terms of testing-tracing-isolating and undermines trust in public health measures. To overcome these difficulties, more elaborate mass testing strategies need to be considered.
Focus testing is suitable for large scale mass testing (province, region, or country). This strategy requires 10% more test that standard mass testing, but increases the positive predictive value 30-fold (from 2,6% to 90%) in low-prevalence areas. Further, the rate of false negatives is kept at acceptable levels.
Double testing is designed for smaller high-prevalence zones (city, county, province).
Compared to standard mass testing, this strategy reduces the rate of false negatives by 50% to 65%, that is infected people who are tested negative, but comes at a cost of 107% additional tests. The combination of the two is also promising: focus testing in low prevalence zones, and double testing in high prevalence zones. An analysis by Miquel Oliu-Barton, associate professor at Paris-Dauphine University) and Bary Pradelski, associate professor at the CNRS, associate member of the Oxford-Man Institute for Terra Nova.