1. Viral Load Ramps Up Early And Declines Slowly
2. The Window Of Infectiousness Is Brief [EDIT: If Caught Early], Only 2-3 Days In Most Cases
3. High-sensitivity tests are expensive, and have long throughput times.
Early tests from the CDC and WHO were designed to be as sensitive as possible. A large part of this was because it was thought that infection buildup took place over days, and thus the need to capture early, lower viral loads. But because the buildup is so rapid, it avails us little. More, because the reagents are so expensive, it is uneconomical to do the tests. Conventional PCR nasal swab tests are expensive, costing "from $50 to $150" each. Mina states that such tests "often have sample-to-result times of 24-48 hours". In the real world of limited lab capacity, I have heard of delays of as much as eight days.
4. Low-sensitivity, rapid, cheap daily tests can work to prevent disease spread.
Because of the rapid acceleration of viral growth early in the infection cycle, a surveillance test needs to only detect a relatively high amount of virus. These tests should be cheap — cheap enough for everyone to use daily, and capable of being mass-produced in the billions.
The good news is that such tests already exist:
E25Bio, Sherlock Biosciences, Mammoth Biosciences, and an increasing number of academic research laboratories are in the late stages of developing paper-strip and other simple, daily Covid-19 tests. Some of the daily tests are in trials and proving highly effective.The bad news is that the FDA still looks at this problem from the standpoint of regulatory certainties, and the understanding we had of disease mechanics back in March. In TWIV 640, Mina participated in the following exchange:
The strips could be mass produced in a matter of weeks and freely supplied by the government to everyone in the country. The price per person would be from $1 to $5 a day, a considerable sum for the entire population, but remarkably cost effective.
Michael Mina: ... [H]igh-frequency testing using a less sensitive test goes much further than low-frequency testing using the best test in the world. We pretty much found that if you test less than ... every two weeks, you're not going to be able to contain pathogens.... What I would suggest is we have really cheap, low-sensitivity, from a molecular perspective, low-sensitivity tests that are a dollar, that people take every day. And so then it doesn't have to catch you in your incubation period, it doesn't have to catch you 20 days later, it just has to tell you the morning of that you have enough virus that you could be transmitting.Mina's faith in the FDA et al. to manufacture anything is suspect given the CDC's role in delaying a working test back in February, but the funding part is much more likely. This sounds promising, which means it will all but certainly be ignored.
Rich Condit: Do such tests exist? Or will they?
MM: You know, they do. So this is the other bit that really led to that. They do exist, and I've been advising a lot of companies on their reagents and their tests and their test characteristics that might be needed. And the most frustrating thing for me is that these tests exist, but they're all getting slammed. Especially when they look at what happened with Abbott IDnow getting slammed for having a sensitivity that's a few Ct values worse than PCR, which is nothing. If you have a sensitivity that gets you to a Ct value of 36, great, that's amazing. But these companies are shaking in their boots, saying we can't go to the FDA, we can't try to market this test yet, because its sensitivity is three orders of magnitude worse than PCR, analytically, on the molecular level. And so I've been saying this: the FDA and the CDC and the NIH have to change their messaging. They have to say, look, there is actually a technology — that a test could exist right now — I have some sitting in my office next to me — they're paper strips. They're just little pieces of cardboard printed with monoclonal antibodies that can pick up an antigen. Essentially a lateral flow assay, can be printed in the millions, and could probably be done by the federal government and be funded by the federal government.