Testing alone won’t contain coronavirus

We need a combination of strategies to stop the spread of COVID-19

The media has become obsessed with testing for COVID-19 as the key to containing coronavirus outbreaks and helping to get life back to normal. 

Much has been made of UK Health Secretary Matt Hancock’s promise to reach 100,000 coronavirus tests per day by the end of April. And public health expert Dr Anthony Fauci has suggested that testing needs to double in the US before lockdown restrictions can be safely eased.‍

Coronavirus testing is a key part of fighting the COVID-19 pandemic. But given the lack of widespread availability of rapid testing and the high rate of false negative results (where people test negative despite being infected) we can’t rely on testing as the only tool to get us safely out of lockdown and through the coming months. ‍

Instead, we need to include other approaches, including symptom monitoring using our COVID Symptom Study app, to support testing and guide responses to the outbreak. 

To find out more, we spoke to Mike Malim, Professor of infectious diseases at King’s College London, and Professor Tim Spector, who is leading the COVID Symptom app research programme. ‍

How does coronavirus testing work?‍

Polymerase chain reaction (PCR) swab tests are used for detecting people who are actively infected with SARS-CoV-2, the coronavirus that causes COVID-19. 

The test involves taking a swab from the back of a person’s nose or throat in the hope of picking up some of the virus. The swab is then sent to a laboratory where any genetic material present in the sample is copied using a technique called PCR, and then analysed to compare it against the known genetic sequence of SARS-CoV-2. 

"The more testing we do, the better,” says Mike. “No test is perfect, but the more of it we do, the more cases will be identified, and therefore the more people will conduct themselves accordingly to try and reduce the spread of the disease to other people.” 

Coronavirus tests aren’t always accurate

‍Despite the pressure to test more and more people for coronavirus, there are still a lot of questions that need to be answered about the testing process and results. 

"It's not entirely clear how long PCR tests remain positive after people are infected, and whether tests could come up negative when people are still shedding virus,” says Mike.

PCR tests are very specific, meaning they don’t give many false positives: if you get a positive result, it’s highly likely you’ve got coronavirus.

However, the tests don’t detect every case of infection, especially if the swab isn’t done correctly and doesn’t pick up any virus or there isn’t enough virus present to show up in the PCR. 

Studies suggest that PCR tests only identify around 70% of COVID-19 infections. That means that for every ten people who have the disease and take a test, three people could get false negative results and still go potentially on to infect others.

“We have to realise that people may need to be tested multiple times, and that a negative result doesn't mean you don't have the virus,” explains Tim. ‍

What should we do if we can’t test everyone for coronavirus?‍

To get a complete picture of the spread of COVID-19, allowing infected people to be identified and isolated, we would need to test huge sections of the population far more frequently than is currently done.

Various organisations - including the CDC in the US and NHS in the UK - are also developing different forms of apps for contact tracing so that people can be informed if they’ve been close to someone infected with coronavirus, although issues are being raised about the effectiveness of contact tracing apps and personal privacy. 

These contact tracing apps are very different from the COVID Symptom app, which only gathers information about your symptoms and health. ‍

The COVID Symptom app does not access your contacts or precise location and does not use Bluetooth. You can find out more about how we secure your privacy and data here. ‍

“It’s all about identifying the cases and then limiting the opportunity for them to spread the disease to other people,” explains Mike.

"How many people do we want to be testing on a daily basis? It's hard to say, but I would say the more testing, the better because you'll have a better understanding of where the virus is and therefore be able to cut down on the transmission rates, and that is what's going to be key to bringing the infection rate down,” he explains.

Unfortunately, current testing levels are much too low and cant be repeated often enough to show us how the disease is moving through the population. ‍

Less than 1% of around a million people reporting symptoms to our COVID Symptom app said they had received a test. ‍

Even among people who reported a combination of symptoms indicating a high risk of COVID-19 (cough and/or fatigue plus at least one of the following: loss of smell, diarrhoea, or fever) only one in five (20%) had taken a coronavirus test. 

(The tests we’re talking about here are designed to detect active coronavirus infections by looking for the virus itself. This isn’t the same as tests that see whether someone has previously been exposed to the virus by looking for antibodies produced later as part of their immune response to infection, known as antibody or serological testing.)‍

We need a combination of testing and symptom tracking to beat coronavirus‍

“We believe that testing is a vital part of the coronavirus response, but it shouldn’t be the only response,” says Tim. "We need a combination of detailed symptom collection plus tests, and the future is likely to involve a combination of solutions, not one or the other."

“I think the COVID Symptom app is a really good tool for finding people who suddenly aren’t very well,” adds Mike “It can give a good indication based on symptoms whether you have a coronavirus infection. And if you do fall into that category, then you should get tested straight away.”

Our COVID Symptom app allows us to monitor how the virus is spreading and identify those at risk earlier. Once you’ve downloaded the app, it takes less than a minute to check in and log your health status, whether you’re feeling well or are experiencing any symptoms of COVID-19.

Right now there are more than 3.3 million people across the UK, US and Sweden using the app to monitor their health, providing vital real-time data on the spread of coronavirus and allowing many scientific discoveries to be made. 

Anonymised data from the app is feeding into national efforts to control the disease and redirect resources including testing capacity to where they are needed most, right from the very first signs of infection. It is also telling us which are the critical early signs to watch out for, even before fever and cough.‍

The truth about coronavirus testing

• Everyone is talking about how testing is essential to fighting coronavirus.
• But testing alone is not enough to contain the disease.
• Current tests are far from 100% reliable, and we can't test everyone frequently enough to rely on testing data alone.
• Symptom monitoring can identify pockets of infection weeks earlier, allowing us to redirect resources and restrictions to contain the disease. 
• Combining virus testing, antibodies and symptom monitoring is the best way to beat the disease

Download the COVID Symptom app and get the latest research updates from covid.joinzoe.com. ‍

Find out more:

• False Negative: COVID-19 Testing's Catch-22 and the consequences of being wrong — MedPageToday
• If You Have Coronavirus Symptoms, Assume You Have the Illness, Even if You Test Negative — The New York Times
• COVID-19 tests: how they work and what’s in development — The Conversation
• The case for ending the Covid-19 pandemic with mass testing —  Vox
• Real-time RT-PCR in COVID-19 detection: issues affecting the results - Expert Review of Molecular Diagnostics
• COVID-19 Testing: The Threat of False-Negative Results - Mayo Clinic Proceedings
• Rapid implementation of mobile technology for real-time epidemiology of COVID-19 - COPE Consortium, medRxiv