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Testing to Reduce the COVID-19 Infection Rate

Dr Ghebreyesus of the World Health Authority makes an impassioned plea for every country in the world to implement COVID-19 testing.

Reducing the infection rate to less than 1 must be at the heart of any policy to combat the COVID-19 pandemic. Any policy aimed at reducing the infection rate requires testing.

In April 2020 Dr Tedros Adhanom Ghebreyesus, Director General, World Health Organisation spoke at a News Briefing.

As I keep saying, all countries must take a comprehensive approach.

But the most effective way to prevent infections and save lives is breaking the chains of transmission and to do that you must test and isolate.

You cannot fight a fire blindfolded and we cannot stop this pandemic if we don’t know who is infected.

We have a simple message for all countries.

[Huge Test ! ;; ;;; Test! ;; ;;; Test!]

Test every suspected case. If they test positive, isolate them and find out who they have been in close contact with up to two days before they developed symptoms and test those people too.

Every day more tests are being produced to meet the global demand.

WHO has shipped almost 1.5 million tests to 120 countries. We are working with companies to increase the availability of tests for those most in need.

WHO advises that all confirmed cases, even mild cases, should be isolated in health facilities to prevent transmission and provide adequate care.

How to beat COVID-19

The message from the World Health Organisation is very clear. To beat the COVID-19 pandemic it is necessary for every country in the world to reduce R₀ by the following policy approach :

break the chains of transmission
to do that you must test and isolate
test every suspected case
If they test positive, isolate them
find all close contacts up to two days before developing symptoms
test those people too
all confirmed cases should be isolated in health facilities

The Over-arching Policy is to Reduce R

Policy in many countries was to save their national health services from being overwhelmed by dealing with the new virus. Policy makers had adopted policies to achieve herd immunity or flatten the curve. Modellers have played a prominent role in guiding policy with politicians in many countries saying that they are following the science. However it is more complicated than that because the science can be ambiguous, contested and inconclusive. Nonetheless decisions have to be and generally those decisions are based on political rather than scientific debate.

One clear thing has emerged: to eradicate the virus its R value must be reduced to less than one, and this requires testing.

The policy proposed by the WHO is to test as widely as possible to identify infected people, and to make it compulsory for those people to isolate while they recover. This requires governments to provide accommodation where people can be isolated.

Would this policy leave a large susceptible portion of the population that might be subject to second or third waves of infection? Or would the same test-and-isolate policy effectively manage all subsequent epidemic breakouts?

This test-track-and-isolate policy makes great inroads into people’s civil liberties. For example, a mother with young children would find it very difficult to leave home. Would isolation facilities need to be available for whole families? Also asymptomatic people working on time-critical projects could greatly resent being forced to isolate from their teams.

On the other hand, an effective isolation policy could greatly reduce the incidence of viral infection making it necessary for relatively few people to be isolated? This and the ‘Test, Test, Test’ mantra is something that we can investigate by Agent Based Modelling.

Testing for COVID-19

The current gold standard which is detecting active cases is the PCR test which detects virus RNA.

“At the moment the majority of the current Covid-19 tests that all the reports are coming from are using PCR [Polymerase Chain Reaction ],” says University of Sussex senior lecturer in microbiology Dr Edward Wright. “They detect the genetic information of the virus, the RNA. That’s only possible if the virus is there and someone is actively infected.” [1]

An antigen is a substance that is capable of stimulating an immune response. … Examples include parts of or substances produced by viruses [2] An antibody, also called immunoglobulin, is a protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies recognize and latch onto antigens in order to remove them from the body. [3]

PCR tests are used to directly detect the presence of an antigen, rather than the presence of the body’s immune response, or antibodies. By detecting viral RNA, which will be present in the body before antibodies form or symptoms of the disease are present, the tests can tell whether or not someone has the virus very early on. “PCR gives us a good indication of who is infected. They can be isolated and get in contact with people they’ve been in touch with so they can be quarantined too, just in case. That’s the true advantage of the current major diagnostic tests, you can break that transmission chain and get a clearer picture of what’s happening,” says Wright. By scaling PCR testing to screen vast swathes of nasopharyngeal swab samples from within a population, public health officials can get a clearer picture of the spread of a disease like Covid-19 within a population. [1]

Antibody-based tests detect the immune response in humans and not the virus itself. They usually involve a blood sample and indicate that a person was infected but may not be infected now.

References

[1] Chloe Kent, ‘Different paths to the same destination: screening for Covid-19’, Medicaldevice-network.com, 3 APRIL 2020, Viewed 11th May 2020 https://www.medicaldevice-network.com/features/types-of-covid-19-test-antibody-pcr-antigen/

[2] Encyclopedia Britannica, ‘Antigen’, Viewed 11th May 2020. https://www.britannica.com/science/antigen

[3] Encyclopedia Britannica, ‘Antibody’, Viewed 11th May 2020. https://www.britannica.com/science/antibody