Tornus

Update 2022-01-07: It's pretty clear now that antigen tests are less effective against Omicron, probably for three reasons: they are less sensitive to Omicron, viral loads rise faster with Omicron than with Delta, and Omicron is more infectious than Delta. Based on the current data, I'm changing two things in the original writing, with the caveat that these are just guesses that are not backed up by hard data: * The test validity window goes from 12 hours to 6 hours. * The likelihood of detecting a person who is infectious but asymptomatic goes from 75% to 50%. Personally, I've started using the throat swab technique: https://www.youtube.com/watch?v=5qHTBlxfNes That technique was likely more effective for detecting Delta, and there are strong theoretical reasons to think it might be much more effective for detecting Omicron. Introduction Home antigen tests for COVID are an imperfect but useful tool. In this post I’ll discuss the four scenarios where I think they’re most useful, share a few thoughts about using them correctly, and finish by taking a deep look at the data on accuracy. If you don’t already understand concepts like sensitivity and positive predictive value, you might want to read this first. I’ll focus on the Abbott BinaxNOW test because I think it’s overall the best and most available home antigen test in the US as of October 2021 (the situation is different in other countries). Sensitivity varies somewhat between different tests, but they are all roughly comparable and have the same strengths and weaknesses. EPISTEMIC STATUS This is a complex topic that is evolving quickly and is only partly understood. My analysis is grounded in hard data but necessarily involves a certain amount of extrapolation. I have no relevant credentials but this writing has been reviewed by a medical epidemiologist who works full time on COVID. Application 1: risk reduction I consider antigen tests to be most useful for reducing the risk of asymptomatic transmis