Public health experts have been clear. In order for countries to safely reopen their economies, they need to know who has the virus. This means identifying as many infected individuals as possible through validated, reliable, and widespread testing.
|Across Asia, governments are setting up mass testing facilities to track COVID-19 infections. Photo: ADB|
But with hundreds of Covid-19 tests flooding the global market, the reliability and accuracy of many tests uncertain, and continuously updated guidance about who should get tested and with which test—navigating the testing landscape is anything but clear.
While some countries have been able to implement mass testing and contact tracing, many others have struggled to achieve this benchmark. For many low- and middle-income countries, widespread testing remains unfeasible due to limited testing capacity—including lack of skilled staff, ill-equipped laboratories, and supply chain bottlenecks.
Countries with testing constraints should therefore consider developing a testing strategy that works within their context. This might include targeting hotspots with potential for high infection rates or providing testing in community settings where patients are already receiving other health or social services. South Africa, for example, mobilized tens of thousands of health workers and sent mobile testing teams into its densely-populated townships—with an initial focus on “hotspots” where infection rates were highest—to identify cases early and avoid overcrowding at hospitals.
Several different technologies for Covid-19 testing have been rapidly developed. These generally include those that test for the presence of the virus (i.e., an individual is currently infected) and those that test for the presence of antibodies (i.e., an individual was infected in the past).
Understanding the range of testing options can help policymakers better develop testing strategies.
Testing for the presence of the virus
Polymerase Chain Reaction (PCR) testing: PCR tests remain the most common and accurate test for identifying positive Covid-19 cases and are recommended by the World Health Organization. The test is highly sensitive and involves taking a sample by inserting a swab into the nose or mouth and sending the sample to a lab for confirmation. Most PCR tests take a few hours or sometimes days to process. Furthermore, even though laboratory-confirmed PCR tests are still the most accurate method currently available for detecting Covid-19, they require a centralized laboratory, trained laboratory specialists, reagents and other supplies, cold-chain logistics, and large numbers to be cost-effective—which presents challenges in low-resource or remote settings.
Due to the need to expand testing capacity more widely, PCR tests that can be administered outside of laboratory settings and at point-of-care (e.g. primary care clinics) have also been developed. Because they can be manufactured more quickly, produce results in only 30 minutes, and are potentially cheaper, these point-of-care PCR tests have the potential to spur faster scale-up of widespread testing. However, because they are less accurate than lab testing and must be designed carefully and validated, they have not yet been recommended by WHO for use outside of research settings.
Pros: Most accurate at detecting current infections
Cons: Longer processing time; requires specialized lab, supplies, and technical skills
Antigen Testing: Antigen tests, which look for the virus’s proteins, can identify people who are currently infected with the virus—including asymptomatic cases—through the presence of antigens in their respiratory tract using a nasal or throat swab. An antigen is a foreign substance, like a virus or bacteria, that induces an immune response in the body. The benefit of these tests is that antigens can be detected with inexpensive, point-of-care or community tests and can provide results in a few minutes. While not widely available, a highly-accurate antigen test could be ‘game-changing’ as it could potentially pave the way for mass community testing at-scale—providing rapid results in limited-resource contexts.
Pros: Rapid; Inexpensive; can be administered in clinical and community settings
Cons: The technology is new and an accurate test is not currently available
Testing for the presence of past infection
Antibody (or Serology) testing: Antibody tests are used to identify individuals that were exposed to Covid-19. The tests measure an individual’s immune response by detecting antibodies through a blood sample. Antibodies typically appear anywhere from 7 to 11 days after exposure and these tests can provide a broader picture of Covid-19 infection spread within a population. They can also be administered at point-of-care and produce results in a few minutes. Many countries hope to use antibody tests to better understand how many people have recovered from the virus. However, questions about the accuracy of current tests have delayed widespread use.
Specific challenges include high false-positive and false-negative results, the consequences of which could be severe. An individual with a false-positive could be subjected to unnecessary quarantine and isolation, along with their contacts. They could also think they were protected against getting the virus in the future, although this has not been scientifically proven. Moreover, an individual with a false-negative would believe they didn’t have the virus and are not contagious and thus could spread the virus unknowingly. Furthermore, there is lack of conclusive evidence about whether the presence of antibodies means that someone is protected against Covid-19.
Pros: Rapid; good at detecting spread of disease in a population
Cons: Cannot be used to diagnose infections; less accurate; high rates of false-positives and false negatives could lead to unduly subjecting people to quarantine and could facilitate further spread of the virus.
Translating testing data into effective policy
Several countries—including the People’s Republic of China, Germany, Denmark, and Norway—have now started to lift restrictions. The common denominator is that these countries have successfully implemented widespread testing and tracing and used this data to inform their re-opening strategies.
At the same time, countries like Germany and the Republic of Korea have recently rolled-out antibody testing to better understand how widespread the virus is within the population, while New Zealand is scaling-up random Covid diagnostic testing to better understand community transmission and guide its Covid-19 elimination strategy. Although more time is needed to see how testing data will be used to fine-tune strategies once countries have re-opened, real-time monitoring of transmission through testing data will be necessary for governments to control spread of the disease and possible subsequent waves of infection.
Until a safe and efficacious vaccine is developed, testing data will play a significant role in how countries engage—socially, politically, and economically. It also provides the strongest evidence on what is happening with virus and how best to stop its spread. Given this stark new reality, every effort should be made by all stakeholders—including government, donors, development partners, and private sector—to make testing for Covid-19 widely available and accessible to all. At the moment, PCR remains the gold standard and serology tests may still not be ready for prime time.
Patrick L. Osewe is Chief of Health Sector Group, Asian Development Bank.