Extensive testing key to fighting virus spread

TESTING is the key to combatting the spread of coronavirus, Scots researchers say.

People without symptoms may be ‘silent carriers’ and identifying them is essential, according to scientists at the University of Aberdeen.

They say lockdowns will not eradicate Covid-19, but the measure is our best approach while we wait for a vaccine or faster and more thorough mass testing.

The research flies in the face of the Scottish Government approach. It believes mass testing is of little use because it only gives a snapshot of whether a person currently has Covid-19.

In Scotland, tests are carried out on patients such as those hospitalised with symptoms.

The researchers constructed a mathematical model using data from early stages of the outbreak in Germany, Italy, Spain, UK and Hubei province in China.

The team estimated that less than 8 per cent of the population in the analysed outbreaks would have been exposed to the infection, but 50-80 per cent of those were silent carriers who did not know they had it.

The researchers say such a low infection rate could mean that if and when restrictions are lifted, the virus could re-emerge.

The team conclude that without thorough and extensive screening, carriers that display no symptoms, currently missed by most countries, will continue to spread Covid-19 widely.

Dr Francisco Pérez-Reche of the University of Aberdeen said: ‘In policy terms, our results demonstrate that the current suppression strategies being employed in Germany, Hubei, Italy, Spain and the UK will not facilitate sufficient levels of herd immunity in the population that would control and eventually eradicate the virus. This leaves the risk of re-emergence of the virus once suppression strategies are lifted, similar to second waves of infection observed in 1918 influenza epidemics.

‘We predict, however, that partial relaxation of ongoing lockdowns could keep the number of daily deaths to less than 100.

‘We suggest thorough testing combined with contact tracing, isolation of infected individuals and social distancing can be more effective to suppress Covid-19 spread than severe lockdowns.

‘At present, however, lockdowns are probably the most effective way to delay epidemics until fast and thorough testing becomes feasible.’

Co-author Professor Norval Strachan said: ‘Unreported cases act as silent carriers and control strategies would need to account for them or be prone to the risk of re-emergence or ineffective suppression of spread.’

Earlier this month, Scotland’s former Chief Medical Officer Dr Catherine Calderwood said the idea testing could prevent transmission was a ‘fallacy’.

On April 2 she said: ‘I have been saying and advising the First Minister and the Cabinet Secretary for several weeks now about the distraction that I think the focus on testing may become.

‘The testing is extremely useful but it is only going to be positive within a short window of perhaps 48 to 72 hours while somebody has symptoms because there needs to be an amount of virus in that person for that to be detected.

‘But the thought that the testing in some way slows the virus or is a part of our strategy to prevent transmission is a fallacy, I’m afraid.

‘The testing gives us more information but the social distancing and all of these stringent measures are what we actually need to prevent spread and prevent serious illnesses and death.’

The scientists’ paper has yet to be peer reviewed but is published by medRxiv – the preprint server for health services.