Has digital contact tracing actually worked?
Studies are beginning to show the result of dedicated campaigns all over the world to get citizens using Covid-19 digital contract tracing apps.
The results are mixed, with the success of digital contract tracing efforts influenced by the timing of their launch, the technical design and implementation and the crucial factor of whether the population could actually be bothered to use them.
MIT Technology Review this week released results of a survey of the public health departments of every state of the United States. The answers weren't encouraging.
"Many of the country's exposure notification apps are underutilized, misunderstood, and not well-trusted-and yet this technology may yet come into its own as a public health tool for future disease outbreaks," Technology Review reported.
It points out that while digital contract tracing efforts last year settled around the exposure notification systems run by Apple and Google for smartphones, each state tended to take its own approach to rolling out and promoting digital contract tracing apps.
Most of the apps were launched late in the piece, in the midst of the winter surge in Covid cases. A lack of trust in the technology didn't help, with some states delaying release of apps over privacy concerns.
Wide variation in usage
Technology Review's survey found a wide variation in the activation of exposure notifications on phones of each state's residents. Of 24 states, plus the District of Columbia who responded, the best was Hawaii with 46%, the worst was Arizona with 1.2%. The magic number is 15% when it comes to the penetration of digital contract tracing that can actually prove useful to contact tracing efforts.
Source: MIT Technology Review
That means 11 of the 23 states would fail to meet that threshold. So did exposure notifications and associated apps actually make a difference in efforts to track down contacts of those infected with Covid-19? Short answer - they don't know. No uniform efforts have been undertaken to collect data on how many people responded to exposure notifications.
"It's about priorities," notes Technology Review.
"State departments did not have the time or resources to look at how well digital contact tracing works; instead, they were focused on doing anything and everything to stop the spread of the virus."
Elsewhere, more promising
Studies have been undertaken in the UK and Switzerland and have more promising news. Oxford University researchers looking at 1.5 million exposure notifications sent out via the UK's NHS app in the last three months of 2020 found that each person who tested positive and used the app to alert others, sent out 4.4 messages on average. That intervention, the researchers suggest, could have prevented between 200,000 and 900,000 cases.
Oxford researchers, modeled the impact of 1.5 million notifications that had been sent by the UK's NHS app between October 1 and December 31, when almost 2 million people were infected with covid-19. Their analysis showed that each person who tested positive and used the app to alert others sent out an average of 4.4 notifications; without this intervention, they projected, there would have been between 200,000 and 900,000 more cases.
They also reaffirmed previous research showing that even modest increases in app usage can make a big difference.
"For each 1% increase in users, we estimate the number of cases will drop by between 0.8% and 2.3%," they reported.
And Switzerland? A study there found that around 1 in 11 notification triggers form the SwissCovid app led to SARS-CoV-2 testing of an exposed contact who subsequently had positive test results.
"These findings suggest that digital contact tracing apps can make a relevant contribution to transmission prevention, with the potential to scale as more persons use the apps," the researchers concluded.
Numbers too small
And what about our own efforts with exposure notifications and the NZ COVID Tracer app?
"It's really hard to say in a country with relatively few cases," notes Dr Andrew Chen, a research fellow in Koi Tū: The Centre for Informed Futures.
But anecdotal evidence suggests exposure notifications can make a difference.
"In January 2021, when a person tested positive in Northland, the fact they had used NZ COVID Tracer regularly meant health authorities had more information to work with, and more confidence that risk of the disease spreading further was relatively low," writes Chen.
"Contrast that to the Valentine's Day cases a month later, and in retrospect we might have avoided a snap regional lockdown."
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