Hubris about testing undermines our COVID response

If we woke up one morning to find that two per cent of cars had been planted with a time bomb, people would surely demand that each car be tested before being let back on the road. For months Nobel Prize-winning economist Paul Romer has used this analogy to build support for the idea that testing provides a way out of the pandemic and associated lockdowns. Testing would enable us to identify and isolate those infected with the virus. People could then go to work again.

Testing’s intuitive appeal is irresistible so it’s not surprising that public health authorities have stressed increased testing in their COVID responses. But testing has in large part failed to fulfil its promise. Instead of freeing us from lockdowns, test results have been used to lengthen lockdowns, close schools and threaten more restrictions.

How can testing fail to stop infections? Answering this question requires talking openly about testing’s limitations.

One of its weakness is simply that people may avoid it. They may decide testing is too arduous. Or they may consider the consequences of a positive test too burdensome. Self- isolating for 10 days or two weeks may be easy for the well- off but for many others it involves considerable hardship. Belgium and France recently reduced isolation to one week, an indication many people do consider longer isolation too onerous.

People will also avoid testing if they believe the wider consequences of their testing positive would be too harsh. Thus if a single positive case would lead to a school closure, people who don’t consider school closures a reasonable response may choose not to get tested. They may also hesitate to get tested if they regard lengthy isolation for people they have been in touch with as too harsh.

Another limitation of testing is that slow testing is almost useless. Test results need to arrive quickly: isolation and contact tracing only work if they reduce the time people spend with others while still infectious. Moreover, wide spread of the virus often renders useful contact tracing unfeasible, as authorities in Toronto have recently had to admit.

Testing thus has weaknesses that can render it incapable of stopping the spread of a virus. We should not just assume public health authorities can avoid all these pitfalls and retain everyone’s incentive to get tested.

The impact of increased testing also depends on how effective people believe testing is in limiting transmission. Paradoxically, the more effective they believe it is, the less effective it may turn out to be. The reason is that if they are confident testing will protect them, people will respond to it by interacting more with others. So if the promise of testing is oversold to the public, it may inadvertently cause more infections.

A final reason to dampen our expectations — perhaps surprisingly, given the emphasis on testing in recent months — is that testing is not actually a proven strategy for disease eradication. Testing and contact tracing did help finally eliminate smallpox in 1977 but in that case their purpose was to find target areas for further vaccination campaigns. The suggestion by some advocates of testing that it could eradicate the novel coronavirus, though interesting and provocative, is not supported by our history with viruses.

Hubris about COVID testing is thus a mistake. If expectations about testing were more realistic, people would rely more on other mechanisms, such as social distancing, to limit their impact on the spread of the virus. Our overall response to the virus would also improve. For example, it would increase our resolve to invest in basic science research into the new disease. Such effort is urgently needed, according to a recent editorial in the journal Science Signalling that bemoans our “nearly monomaniacal” focus on testing.

Nor should hubris about testing dictate whom we test. Unlike in the car bomb analogy, we are not all equally likely to die if infected ( and neither does the virus kill two per cent of those it infects). The mortality risk is a thousand times higher for old people than for young people, which means testing should prioritize those who interact with the most vulnerable. Some testing advocates have in effect favoured the opposite by suggesting that schools can only open safely if all children and teachers are tested. The successful reopening of schools in Europe in May belies that. Mass testing in low- risk settings also sends misleading signals about who is most vulnerable to the virus and may also foment unfounded fears in the population.

Testing advocates are doubtless correct that cheaper, faster, and more accurate tests are coming. But it obviously would be unwise to base testing policies and economic recovery on technologies and resources that do not yet exist. Neither should we assume that even daily testing will stop infections or remove the fear that our current focus on cases and case counts is sowing in society. Tests will always be more useful if such hubris is replaced with humility about what testing can reasonably be expected to achieve.

TESTING HAS IN LARGE PART FAILED TO FULFIL ITS PROMISE.