SINGAPORE - Since the pandemic began, Covid-19 contact-tracing apps have become widely used around the world, and mostly work the same way by alerting users who have been exposed to a confirmed case.

But such apps would be even more effective if they could warn users of potential future exposures instead, and help them take precautions and avoid being infected altogether, said Carnegie Mellon University mathematics professor Loh Po-Shen.

This is the concept behind Novid, an app developed by Prof Loh, which acts as an early warning system by tracing a user's network of regular contacts ahead of time.

Using the same Bluetooth technology that enables apps like TraceTogether to work, Novid creates a map of contacts defined by degrees of separation. A family member you see daily and have direct contact with would be a first-degree contact, and that family member's co-worker, whom you may never meet, would be considered a second-degree contact.

It also uses ultrasound to determine whether there was any close, prolonged interaction between users. This is defined as being within about 2.75m of another user for at least 15 minutes.

When an interaction is detected, the phones play an ultrasound signal, which can be picked up by the microphones but are inaudible to the human ear, to estimate the physical distance between the two users.

The app then alerts you shortly after someone in your extended network - up to 12 degrees of separation away - reports a positive Covid-19 test result, and how many degrees of separation there are between you and the "closest" confirmed case.

The infected person is not identified to preserve anonymity, and only information about the degrees of separation and the number of cases in a user's network are revealed.

The app also does not collect location data, nor does it store or transmit personally identifiable information to any external server. These privacy claims were independently reviewed by researchers from Georgia Tech Research Institute in 2020.

In September, Prof Loh left a comment on a Facebook post by Prime Minister Lee Hsien Loong explaining Novid's concept and expressing his interest in collaborating with the Government.

PM Lee replied that he had passed the information to Singapore's Government Technology Agency (GovTech) to take a closer look.

Prof Loh said GovTech has since contacted him, and he has shared more information about his research.

When asked for more details, GovTech said it welcomes ideas from stakeholders and technology experts, and will review them accordingly.

Prof Loh, an American born to Singaporean parents who moved to the United States in the 1970s, thinks this approach to contact tracing could be a game changer for a future pandemic, which might be even more deadly than Covid-19.

"The hardest thing in a pandemic is to get people to take actions that reduce their own freedoms to protect everyone else, but what we came up with is a system where even purely selfish behaviour helps to control the disease," he said.

"The standard contact-tracing app tells you when you are at risk of transmitting the virus, and you need to isolate yourself to protect others.

"Our approach is to give you information about how close the virus is to you, so you protect yourself by cutting back on activities to reduce your own probability of infection even before exposure."

Novid has been deployed on a small scale in communities like Carnegie Mellon University's staff and student population.

One drawback is that it requires users who have been infected to manually update their positive test result. This is unlike official apps such as TraceTogether, which are integrated with national health systems and can update users' infection statuses automatically.

Associate Professor Alex Cook, vice-dean of research at the National University of Singapore Saw Swee Hock School of Public Health, said the concept behind Novid is "ingenious" but would require support from the Government or agencies like GovTech and the Health Ministry to be successful.

"Ideally, the Novid principle would be adapted into the TraceTogether app itself, perhaps with an opt-in option," he said.

"That would give great reach to this, which would boost the overall impact. Otherwise, it means users would effectively need to have two apps running on their phone."

Prof Cook said the main benefit of Novid's approach is that it shifts the responsibility for taking precautions to individuals who are motivated to protect themselves, rather than government mandates.

This would complement the current shift towards home recovery and reduced manual contact tracing, he added.

"If you knew that you were five degrees of separation from any known cases, you'd probably feel fairly safe to go about with socialising and other activities, but if you are just two degrees away from a case, I imagine most of us would feel a bit more concerned and cut back on social activities," he said.

Associate Professor Hsu Li Yang, infectious diseases programme leader at the Saw Swee Hock School of Public Health, said the app's approach of using one's network of social contacts to forecast risk of infection is an interesting and clever concept that differs from the majority of other contact-tracing apps.

However, he said it is debatable if such an app is still helpful for Covid-19 when vaccines are widely available and have been taken by the majority of the population. He also noted the current approach is to dial down on anxiety and fear about the virus.

"But I can certainly see its utility for future outbreaks and other communicable diseases," he added.

HR administrator Don Ng said he would find it helpful to know if infections in his personal social circles are rising or falling. Mr Ng, who is in his 30s, has a son in pre-school, and his parents are in their late 60s.

"Sometimes I don't really know what to do with the national figures because it's hard to visualise how they affect me. We are moving to endemic, so we will probably all know someone who is infected soon," he said.

"Even so, if I knew that a friend of a friend was infected, it would feel more real. If that happened, I would try not to go out too much, or take extra caution around my parents."