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With A Limited User Base, How Effective Are Contact Tracing Apps?

Contact tracing apps have been lauded as one tool to help contain the spread of COVID-19, but they all require a majority of people to download and use them. As more apps come online, the potential user pool for any one app shrinks. 

And that pool is already relatively small. A 90.5 WESA/Campos COVID Insights Study conducted between Sept. 25 and Oct. 9 found that only 4 in 10 southwestern Pennsylvania residents are likely to download contact tracing apps.

An Oxford University study published in April hypothesized that if 60 percent of the population used a contact tracing app alongside other public health measures, the spread of COVID-19 could be substantially reduced. It also estimates even a lower percentage of users would still result in a reduction in the number of cases and deaths.

But those theories assume an entire population is reporting to the same database.

State health officials have strongly encouraged Pennsylvanians to download the COVID Alert PA app to track the spread of COVID-19 in their communities. The app, which launched in September, sends users alerts if they’ve been in contact with someone who tested positive for COVID-19 in addition to providing advice about testing and symptom tracking. The app has racked up more than 565,000 downloads since September. It also interfaces with similar apps used by several other states. 

An alert sent though the National Emergency Alert system on Nov. 25 about the increasing number of COVID-19 cases in Pennsylvania pushed the state app, saying “Stay up to date on the spread of COVID in your community so you can protect your loved ones with the COVID Alert PA app.” 

In the spring, Carnegie Mellon University launched NOVID. It was the first app of its kind released in the United States. Developers say the app has been downloaded about 90,000 times so far. NOVID also promises to notify users who have come into contact with a user who has reported themselves positive for COVID-19. Both use Bluetooth chirps to detect nearby devices that are also running the apps.

In a July update, NOVID added an early warning feature that shows users their contacts up to 12 degrees of separation away. The pro-active approach could help people protect themselves sooner, but it also could create unnecessary worry, according to Dr. David Dausey, an epidemiologist and Executive Vice President and Provost at Duquesne University.

“We don’t want to get to a point where we’ve got everybody in the country quarantining themselves because of six degrees of separation,” he said. “Not every contact [with a positive case] is going to be a contact of concern.”

A spokesperson for NOVID argues the early warning feature is a tool to avoid exposure, not a quarantine recommendation. “With this new approach in mind, exposure notifications are not only much less likely to happen, but are not our goal. We want to give people the power to avoid exposure rather than informing them that they need to quarantine,” they said.

But sending too many exposure notifications isn’t the only issue with some contact tracing apps, according to Dausey.

Dausey said for now, most contact tracing apps don’t capture the nuance of an exposure the way tracing over the phone can. “They don’t have people saying what that contact looked like and whether or not they were wearing masks and all of that. That’s beyond most of these apps,” he said. The Centers for Disease Control and Prevention qualifies an exposure as contact within 6 feet for a total of 15 minutes or more with an infected person.

Investigating disease outbreaks requires a high level of specificity, according to Dausey.

Contact tracing apps also depend on crowdsourced information, “and how accurate that information is,” Dausey said. He said human driven contact tracing remains the most useful to prevent the spread of COVID-19. Contact tracing over the phone allows for trained tracers to ask follow up questions that can better characterize a potential exposure that might not appear on a questionnaire.

When given the choice between privately developed apps like NOVID and government apps like COVID Alert PA, Dausey said he would prefer people respond to local public health authorities completing manual contact tracing. But, he noted, COVID Alert PA collects information to be used by those authorities, making it more useful.

Dausey thinks private apps like NOVID, which focus on preventing exposure proactively, could be useful in the future.

“COVID has really been kind of a trail run” for these apps, he said. “Might these approaches be useful for future outbreaks and future [pandemics]? Absolutely.”