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TThe principles of managing infectious disease outbreaks, whether measles, tuberculosis, or Covid-19, are similar. Identify who has been infected by testing for the disease, find out where they acquired the infection and who may also have been infected by tracing contacts, and stop the spread by asking those affected to isolate themselves. People who become infected are treated with therapies that modify the course of the disease.
Sounds simple right? Now think about how you could implement this strategy on a global scale, for a disease that no one knew existed 12 months ago. This is where organizations like the World Health Organization (WHO) come in, providing leadership, expertise and coordination. Since early 2020, the WHO has been working with different groups to support the development of coronavirus testing, tracking and isolation programs. . She has rightly advocated that everyone should have access to these things, no matter where in the world they live.
The problem is that testing for Covid-19 is expensive and the labs required to process the tests are not available in many countries. Covid testing is most often done using polymerase chain reaction (PCR) -based testing, which requires clinical samples, often obtained by trained healthcare workers, to be delivered to labs with sufficient resources and staff. of highly trained healthcare workers.
In this context, the recent announcement by the WHO that A new type of Covid test to be rolled out around the world could be groundbreaking. Two new rapid diagnostic versions, one made in the US and the other in South Korea, are as simple to use as a pregnancy test and will be supplied to low- and middle-income countries for less than $ 5 each. . Importantly, they do not require access to laboratory or scientific equipment to produce a result. They still need a clinical swab to take from the person being examined, but work is underway to develop similar tests that only need saliva samples or nasal swabs to work, which are much easier to collect. One of the tests has already received emergency approval from WHO; the other is expected to get it shortly.
The new rapid diagnostic tests detect Covid-19 antigens (proteins that are part of the virus) rather than the genetic material of the virus, and can produce a result in less than 30 minutes. In contrast, the turnaround time for PCR tests can be hours or even days. The new tests have been evaluated in communities where there is a high level of coronavirus transmission and have been shown to be most effective in detecting the disease among two days before the onset of symptoms and 5-7 days after symptoms have become evident. This is the time when the amount of virus present in a person (known as “viral load”) is at its peak.
Under these conditions, the “specificity” of the new antigen tests, which refers to the proportion of people who do not have the infection and who test negative on the new antigen test, compares well with the PCR test. So does its “sensitivity,” the term given to the proportion of people who do have coronavirus and generate a positive test.
The coronavirus has magnified inequalities in access to healthcare around the world. Currently, high-income countries are conducting around 290 tests per 100,000 inhabitants, while low-income countries can conduct around 14 tests per 100,000 inhabitants. The ability of low- and middle-income countries to effectively contain the virus and stop its spread has been limited by their access to scalable, affordable, reliable and easy-to-use tests. These new rapid diagnostic tests are a big step forward in this regard.
But these new tests are not only important for low-income countries. They could also be useful in high-income countries. In countries such as the United Kingdom, where testing capacity has proven ineffective and slow against a rapidly spreading virus, these new diagnostic tests could be used to investigate localized outbreaks when demand exceeds the capacity of testing facilities for PCR.
WHO is working to implement these tests worldwide, particularly in continents such as Africa and South America that currently do not have access to sufficient testing resources. One hundred and twenty million of the new tests have been obtained and will be implemented starting next month. But WHO only has seed funding to support this program and urgently needs additional funding to ensure that it reaches as many people as possible.
Although PCR testing will remain the “gold standard”, the new rapid antigen tests are a useful tool to control the pandemic. As we have often heard during this crisis, viruses do not respect national borders. Therefore, it is critical that all nations are able to offer effective testing, contact tracing, and isolation programs. Ensuring that low-income countries have cheaper, easier and more reliable tests is not just a moral issue. It is also good science.
• Dr. Charlotte Summers is Professor of Intensive Care Medicine at the University of Cambridge.
