The overall effectiveness of contact tracing varies wildly depending on the location. If NYC fully reopens and goes back to "normal" a typical resident might ride the subway five stops to get to work. Each subway car holds 260 or so people at rush hour. At each stop, some people get off and some more get on. An infected person might expose 500 or more people just riding the subway to work as the passengers in the car get on and off. Once they get to their stop and get off, they're then passing through the people waiting for a train and the people on the street. A few hundred more people could easily get exposed. Then in their workplace, they're likely to be in contact with more people and if they go out for lunch, still more people. Then they've got the walk back to the subway stop, the wait among others for their train, the trip home, making five more stops on the train and then finally they're back home. If they don't go out that night they've likely exposed over a thousand people just by going to and from work.
Then all of those who came into contact with the infected person need to be monitored and traced, as they could be unwitting carriers spreading the disease. And if they have similar levels of interaction and travel then each of them is potentially infecting a thousand people a day and all of those people need to be traced. If you have a thousand people exposing a thousand people each day, that's a million people a day. The numbers get crazy quickly in large population centers.
Contact tracing breaks down very quickly in large population centers. If you're doing it in the middle of nowhere, it can be effective, but in large population centers, you might as well just assume everyone has come into contact with someone with the virus. Contact tracing just doesn't work in large population centers.
We now know one of two things about this virus. Either the virus isn't as easily spread as first assumed, or the virus isn't nearly as dangerous as first assumed with many people getting it with no symptoms and just shrugging it off. And it's possible both are true.
If each person with the virus, infected just one uninfected person each day, by day 35 everyone in the world would have had the virus. Day one, one person has the virus. They give it to someone else and on day two there are two. Each of them then infects someone else and on day three there are four cases. Each day the number of cases doubles from the day before and by day 35 over eight billion people are infected. That clearly hasn't happened.
Antibody studies in NYC have shown that between 20% and 25% of residents have likely been exposed to the virus and formed antibodies. (Assuming the antibody tests are reliable which may be assuming a lot.) That implies that most people just shrug off the virus with few if any, symptoms or ill effects. There are 8.4 million people in NYC. If 20% of them have been infected and recovered then that's 1.68 million people. Almost the total known number of infected nationally.
We're a country of about 330 million people. We have 1.76-ish million confirmed cases of Covid-19. That puts your odds of bumping into a known infected person about one in 187. (It's even safer than that as many of those confirmed cases have either recovered (around 94% recover) or died.) Based on what we now know, just casual contact with an infected person is very unlikely to spread the disease. (Once again if each infected person infected just one person a day we'd all already have had it.) So, the risk to each individual at this point is pretty small. If you practice safe behaviors, (mask, handwashing, etc.) the odds of you getting infected are very small.
Contact tracing will largely just make people paranoid. For people who live in large population centers, they'd get ten or more notifications a day that they'd come into contact with an infected, or possibly infected person. If you think people are stressed out now, the level of stress will increase dramatically if contact tracing is deployed. If everyone who has come into contact with an infected person self-isolates, we'll become a country of hermits all living in self-isolation.
Just do what you're supposed to do and you should be fine. This isn't the plague to end all plagues. Contact tracing is a tool that's largely ineffective in large population centers and is far from a panacea. Just wear your mask, wash your hands, and you'll likely be fine.
Fly!!! Eagles!!! Fly!!!
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