Thread by @michaelmina_lab

Rapid tests work very well to answer 🧵
AM I INFECTIOUS and a RISK TO OTHERS

This is THE public health ? we care about

I made a BIG chart of rapid tests

- Overall sensitivity vs any PCR pos - what FDA judges

- Sensitivity if infectious (97%!) - what we actually care about

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This data above comes from the UK COVID-19 Lateral Flow Oversight Team.

What the data above shows is that rapid tests are excellent public health tools to quickly identify almost anyone who is currently infectious and needs to isolate

What it also shows is...
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This shows why there is so much damn confusion about if rapid tests are sensitive

Answer: YES they are... if the question is "Am I Infectious Now and do I need to isolate"

However, if we compare them to PCR, then we are asking a different question: Do I have any RNA in me

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For Public Health, we want to identify & isolate (+ trace) ONLY ppl who are currently infectious. And, if someone is currently infectious, then we must know FAST - not tomorrow (duh) and definitely not in 3 days!

We don't care much about if someone was infectious last month.

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So, rapid tests are perfect public health tools!

Rapid Tests continue to get a bad wrap bc Docs (& regulators) fail to distinguish:

A Med Device: Do I have any RNA in me, even if from an infxn 3 weeks ago... & I don't care how long the result takes
vs
A Public Health Tool!

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We must define the tools we are using during this pandemic

We cannot keep putting public health tools in the same bin as medical devices

It is THE reason we lack these critical public health tools in the US - bc FDA is asking them to do something they aren't designed to do

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There is a solution for US to accelerate access to tests
We just define these PUBLIC HEALTH tools - during a PUBLIC HEALTH emergency - as... PUBLIC HEALTH tools & not medical devices

Simple?

Then, CDC can evaluate them based on *public health* metrics
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https://twitter.com/michaelmina_lab/status/1435367919865712644?s=20

The chart in the First tweet of this thread is adapted from this terrific paper by the UK COVID-19 Later Flow Oversight Team - which has (arguably) had the most experience using and evaluating rapid antigen tests in the world now.

medrxiv.org/content/10.110…
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Also, the chart not only shows Sensitivity, but also Specificity

For Public Health especially, It's extremely important to have high specificity so we don't get a lot of false psitives. These top tests have great specificity with only 0 or 1 in 1000 turning falsely positive.

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This graph shows relationship between time, viral load and transmissibility - and why Sensitivity against PCR looks horrible, even if the test is 100% sensitive to catch infectious people.

The infectious period is days. PCR is not specific for this & stays pos for weeks

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Why is Defining a rapid test as a public health tool so important?

it's because there is a massive supply of rapid tests across the globe yet very few are available to American's bc we regulate them as medical devices... making it nearly impossible to gain an FDA EUA.

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This is because when defined as a medical device, the comparison is to the gold-standard medical device: PCR.

As the data in the first tweet in the thread shows, a 100% sensitive & specific test for being contagious will only have a 50% or lower sensitivity against PCR...

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The reason is simple

The gold-standard PCR FDA requires rapid Ag tests to compare to is NOT SPECIFIC for the public health ? being asked: Am I infectious?

It's not that rapid tests have low sensitivity - it's actually that the PCR has low specificity for a public health ?

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