"This policy brief discusses the role of testing for COVID-19 as part of any plan to lift confinement restrictions and prepare for a possible new wave of viral infections. If all confinement restrictions are lifted before a vaccine or effective treatments are developed without other measures to suppress new infections, the infection rate is expected to rebound rapidly. Crucially, quick suppression of infections requires testing more people to identify who is infected; tracking them to make sure they do not spread the disease further; and tracing with whom they have been in contact. This brief discusses how testing strategies can be used to achieve three main goals: 1)suppressing the resurgence of local outbreaks; 2)identifying people who have developed some form of immunity and can safely return to work; and 3)gaining intelligence on the evolution of the epidemic, including on when a threshold for herd immunity has been reached. The brief discusses whattests can be used for each goal, as well as practical implementation issues with testing strategies, including the opportunities and risks of using digital tools in this context."

Key messages

• A key question behind any strategy to ease confinement restrictions and reopen economic activities is how to avoid a new spread of the SARS-CoV-2 virus that would necessitate further lockdowns. Once the number of infected people has successfully been brought sufficiently down, quick suppression of new waves of viral infections will be key. Testing strategies are central to achieve this.
• There are two types of tests. First, molecular diagnostic testing (RT-PCR) helps to identify those individuals who are infected at the time of the test. An effectivestrategy that tests, trackspeople infectedand tracestheir contacts (TTT), helps to reduce thespread of the virus and thus bring its reproduction number below one.
• Given the characteristics of this coronavirus–including the large number of asymptomatic cases and high reproduction number –to be effective at suppressing the spread of the virus, the TTT strategy should be used very widely, requiring a very large proportion of all cases (between 70 and 90%) to be traced to prevent a new outbreak of the virus. This would require increasing capacity for testing enormously; putting in placestrict measures to prevent people who may be infectious from breaking quarantine; as well as identifying ways to trace contacts,which may push the limits of privacy concerns, unless new approaches to digital tracing, currently under development, are put in place.
• Significant logistics and capacity constraints –ranging from the availability of trained personnel to take accurate specimen, to the time required for laboratory analysis and the availability of reagents –have impeded more widespread diagnostic testing in many countries so far. Recent development of faster RT-PCR molecular diagnostic testing, which can be deployed at the point of care, should help scale-up capacity for effective TTT in countries. Digital enabledcontact-tracing can help improve the speed and effectiveness of TTT strategies, as seen in some countries.
• A second type of test –so-called serologic test –detects people who have had a prior infectionand thus developed antibodies. Such tests can be used for two purposes, namely to allow people who have acquired immunity to return to work safely, and to provide intelligence on the evolution of the epidemic across the population. Rapid serology test kits need to be developed and their clinical performance needs to be demonstrated before deployment at scale can happen.
• Despite the fact that a relatively low number of people have so far been infected and thus we are still far from herd immunity, the successful implementation of serologic testing strategies at large scale can help reduce the spread of the virus and complement the TTT strategy. This will also require major efforts, including: 1)verifying the clinical performance of tests, particularly for rapid serologic tests; 2)preparing procurement and logistics arrangements to scale up production and deployment of the tests, and train and deploy human resources, particularly for diagnostic RT-PCR tests; and 3)providing adequate safeguards to protect civil right and privacy of populations while deploying or apps-enabled tracking strategies."