I’d wear a CovidCard. The question is, should you?

I’m OK with wearing a CovidCard. But are you? There’s no point me doing it alone.

I didn’t know much about the CovidCard proposal until I read Dave’s latest blog post. You would wear the card visibly on your person. It would exchange encrypted ID numbers with other nearby CovidCards via Bluetooth; and store a record of those “contacts”. It would be a supplement to other contact tracing methods.

The idea is that if you test positive for COVID-19, then the ID numbers recorded on your card can be matched to a central database; generating names and phone numbers of your contacts for COVID-19 contact tracers to follow up. Cards belonging to these contacts will also reveal ID numbers for people who can then be traced and tested, etc. No contact data leaves your card under normal circumstances – only when tracing your contacts once you are known to be infected or when you have come into contact with someone else who has been.

Trace, test & isolate

The point of contact tracing is to find people that have been exposed to the virus before they would find out otherwise (eg, by becoming sick themselves and visiting a health clinic). Having found such people, authorities can isolate them, reducing the chance of them infecting others.

CovidCards could assist with this process, because they can supplement faulty memories and incomplete records, and because they can record contacts with those whose names and contact details we don’t know.

A solo CovidCard helps no-one

Wearing a CovidCard does not help you directly. It does nothing to prevent you getting sick. But should you come into contact with an infected person and you can be easily traced, it does reduce the chances that the infection will be passed on to your contacts, and their contacts, etc.

How many of us need to be wearing cards for this to be an effective supplement to contact tracing? If I wear a card it’s only useful if my card encounters other cards to “talk” to. The higher the card-carrying rate the greater the number of contacts recorded – if we all wear cards then all contacts would be recorded.¹

In reality, not everyone will wear a card. In theory, if our daily interactions are completely random and 71% of the population wear cards, then the card system will only record 50% of contacts between people in the population (as coverage is the square of the adoption rate).² 50% is not ideal, but still a lot better than relying purely on people’s memory as to where they went and who they interacted with.

Of course, our interactions are not random. So, we need to think more about the sorts of people that should be given priority to receive one.³

What about me?

My contacts are not very random – I meet the same, limited number of people at work each weekday. And in the evenings, I don’t go to nightclubs; I can be found at home watching Netflix with my significant other and the cat. In the weekends I meet even fewer people. I use public transport during the week and move through Wellington Central Railway Station at peak times of the day. I don’t think I’m especially vulnerable to COVID-19 but said significant other is immuno-compromised, and I have recently been down South to visit my mother who is in her 80s. These reasons would motivate me to wear a card, but the main reason is that I think the card could be effective in supressing the disease more widely. But my wearing it doesn’t help much unless many others do too, which is why I’d hope for a high voluntary adoption rate. Mandating adoption could push the rate higher.³ But if they are in short supply, then I’m hardly a priority.

What about the elderly?

Older people, should they become infected with COVID-19, have a much higher risk of dying than do younger people. Does that mean they should limit their interactions with others? Not necessarily. Elderly people typically have fewer daily contacts than the general population, and those contacts are less likely to be random. And maintaining the contacts they have is very important for their health and wellbeing.

But while the consequences of catching COVID-19 are more serious for the elderly, a CovidCard won’t protect them from those consequences. Further, even if they do get infected, they will probably have few contacts before symptoms develop. By this logic, older people would not be a priority for receiving CovidCards. If they do become infected with COVID-19 then their contacts could be traced by other means.

How about health professionals?

If CovidCards are limited, then it might be more important that health professionals (eg, doctors, nurses, pharmacists) and rest home workers use them. Health professionals come into contact with many (potentially vulnerable) people and they come into contact with each other professionally, and often socially, as well. The chances of COVID-19 spreading among health professionals and for the consequences of that spread to be serious warrants mandating card use among the health (and allied) professions. It just becomes part of the kit of doing the job.

And what about people in border quarantine and those working at the border?

All known active cases of COVID-19 in New Zealand today are in border quarantine. So, the people most at risk of contracting the disease are their contacts – those in border quarantine and those working with them. All these people are prime candidates for CovidCards.

Who gets the (scarce) CovidCards?

This discussion leads me towards a more general conclusion. CovidCards are most valuable for people who meet one or more of these criteria:

1. A high probability (relative to the general population) of having or catching COVID-19.
2. In frequent contact with people meeting criteria (1).
3. A high total number of contacts.
4. In frequent contact with people more likely to suffer serious consequences should they catch COVID-19.

Those in quarantine, or working in quarantine facilities, likely meet criteria (1). Those working at the border likely meet criteria (2). Aircrew might meet (1), (2) and (3). Aged care workers meet (4) and may meet all other criteria. Health care workers are a more varied bunch, but most will meet one criterion, and some will meet all 4.

Sadly, I don’t make the cut. So, while I would wear a CovidCard, I can’t – or at least shouldn’t – claim a spot at the head of the CovidCard queue.

Notes
1. Subject, of course, to the foibles of the technology. The card’s batteries could go flat, or its electronics fail. And a card in a handbag, wallet, daypack or back pocket may be “invisible” to nearby cards.
2. See https://www.bunniestudios.com/blog/?p=5820 for a more detailed explanation of this relationship.
3. The CovidCard would not be fully deployed until 2021.

Photo: The author modelling a (fake) CovidCard.