COVID-19 tests, a scientist’s opinion
Interview with Prof. David Heymann, Professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine, head of the WHO response during the SARS1 epidemic.
What are the key-ingredients for coming out safely from the COVID-19 lockdown?
First, countries need mechanisms to rapidly detect and respond to infections, trace contacts of infected people, surveil them, and isolate them if they become sick. Second, they also need a system to understand the level of past infections: it is important not only to monitor the level of antibodies in the community, but also to map the evolution of this level over time. That is, you need to know the baseline of transmission and monitor it over time.
What is the role of tests in this scheme?
As countries begin to unlock, they will need testing skills. In order to detect infections, they need the PCR tests to diagnose acute illness. At the same time, they need antibody tests to understand where infections have been transmitted in the past, so they can make sure that they pay special attention to those areas. Countries need a system to identify both people infected in the past – through antibody tests – and those acutely ill – through PCR tests. They should make sure they have an influenza-like surveillance system, or ILI surveillance.
What does ILI surveillance mean?
It’s a system run by general practitioners and others. When they receive a patient who has Influenza-like illness, they do a flu test and report to the surveillance system. Europe has ILI surveillance. It should be adapted to test also for COVID-19, in order to understand what’s happening and where the virus is.
The typical antibody tests, the ones that look like a pregnancy tests, are known to be very imprecise.
Lateral flow rapid diagnostics has less than desirable sensitivity. We know that in China and South Korea it has been very difficult to detect antibodies in people with mild infection.
Will rapid diagnostic tests be useful?
It’s not yet clear. None of them have been really validated. We don’t know yet whether quick tests are reliable enough.
Some people see these tests as a way to spot COVID-19.
Some of these rapid antibody tests are claimed to determine not only IgG antibodies, but also IgM ones. IgM are produced early after infection, and could be used sometimes in diagnosis of acute infection. But that’s not yet understood. In the future, an IgM test could be useful to detect infection, but not now.
So do these test have any utility whatsoever?
These tests are useful for purely epidemiological understanding, at this point of time. Some countries were talking about [using them to assign] immunity passport [to individuals with antibodies]. But nobody understands whether those antibodies provide protection and for how long.
How would you recommend to deploy testing?
I would advise good surveillance to detect patients, and routine outbreak containment activities. Tests should be available for surveillance, to understand where disease is occurring. They should be available at health facilities for patients coming in with symptoms. They should also be deployed in contact tracing, when contacts that are under a period of isolation and quarantine develop symptoms, and need to be rapidly tested. But there are two important things before that: continued physical distancing and handwashing; and making sure that, if you are sick, you isolate yourself and wear a mask. Voluntary contact tracing apps may also play a role.
What are the lessons learnt from SARS that could be applied to COVID-19?
Countries in Asia that had SARS and MERS outbreaks were much better prepared than others. South Korea, Taiwan, Hong Kong, and Singapore had excess hospital capacity, they started outbreak containment early, and instead of shutting down all their economy, they locked down specific areas. That’s a lesson they had learnt, because they had seen an outbreak first hand.
In other countries, even experts were taken by surprise: why?
I don’t know why. However, countries have shared information with the WHO, despite geopolitical tension, and the WHO has helped the world understand about the virus by sharing that information. I think the WHO worked.