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

1/ Image
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...
2/
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

3/
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.

4/
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!

5/
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

6/
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
7/
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…
8/
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.

9/
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

10/ Image
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.

11/
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...

12/
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 ?

13/

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More from @michaelmina_lab

11 Sep
Notes on sensitivity of rapid Ag tests for what matters: detecting infectious ppl

Sensitivity:

- Highly infectious (ie superspreader levels): >99%

- Moderately infectious (ie infect 2 or 3 ppl in a classroom): 90-95%

- Mildly infectious (ie spread to spouse only) ~80-90%

1/
This Graph of viral load over time helps to explain this sensitivity issue:
Further, symptoms vs no symptoms has no impact on test performance. Studies that say it does are not recognizing the sampling bias that enters their studies.

3/
Read 4 tweets
9 Sep
This is tremendously good news! (Thread)

@POTUS fully supporting scale up of rapid at-home tests

I've been arguing for this - the Defense Productions Act to be invoked since early last year to drive production of rapid tests

Testing in a pandemic is a Public Health need

1/
While I am tremendously happy to hear the President say this.

I do have my reservations:

Time is of the essence. If we start the scaling process now, it will take a long time.

Meanwhile many many tests exist globally. We could be using those for the time being.

2/
Importantly, I worry that the 280 million tests that are going to be purchased and produced with the use of the DPA... well, that's less than one test per person over the course of a year. The number sounds big but we do have 330 million ppl in US.

But it is a great start!

3/
Read 10 tweets
7 Sep
Dear @POTUS Biden,

The US is at a critical point & we need greater access to faster tests

Rapid tests are barely available bc they're regulated here as MEDICAL tools-holding them back

Please write an EO that makes COVID testing in US a Public Health good

Thanks
Ppl of the USA
These tests are regulated by FDA as medical devices. Which has greatly limited them!

For pandemic control UNDER AN EUA FOR A PUBLIC HEALTH EMERGENCY, rapid tests should be regulated as critical public health tools, vetted (appropriately) by CDC/NIH.
I had the opportunity to speak to the prior administration about this. Unfortunately it didn't go far despite many ppl trying.

I hope that an administration as forward looking as yours (@POTUS ) would see the benefit of an executive order that stops this deadly silliness.
Read 4 tweets
7 Sep
Did you know:

A test *not* performed has a sensitivity of 0% for symptomatic and asymptomatic ppl

A test w a 48 hr delay has 0% during the days of waiting

I talk a lot about sensitivity- but if we want to detect infectious people - frequency of testing is even more important.
And of course, the papers to back it up:

2/
nejm.org/doi/full/10.10…
And Test Sensitivity is secondary (way down the list) to frequency and turnaround time for using testing as a public health tool.

science.org/doi/10.1126/sc…
Read 5 tweets
7 Sep
Did you know

A test that is 100% accurate to detect infectious ppl will only *APPEAR* to be 30%-60% sensitive when compared to PCR-particularly asymptomatics

Why?

PCR stays positive LONG AFTER contagious period

for Public Health, PCR is NOT Specific - it’s a wrong comparison
Although rapid tests are not 100% sensitive to detect infectious levels of virus, they are >95% and do approach 100% for “superspreader” levels of virus.

We just (ignorantly) continue to compare them to PCR - which has led to massive confusion.

2/
This issue with PCR has caused us to isolate millions of ppl who were no longer infectious and lead contact tracers to trace and quarantine many many millions who were never exposed.

3/
Read 6 tweets
7 Sep
With all the news of vaccines & immunity, did you know measles infections destroy immunity and cause “Immune Amnesia”, increasing risk of all other infections

Our research in ‘15 & ‘19 discovered this & the abbreviated story is written up nicely here:

1/
medicalrepublic.com.au/the-great-meas…
In 2015, along w Bryan Grenfell and colleagues, we discovered an exceptionally strong relationship between measles epidemics and all cause childhood mortality - following outbreaks of measles, child mortality was increased for 2-3 years.

2/

science.org/doi/abs/10.112…
We hypothesized then that measles was destroying B cells and plasma cells responsible for retaining immune memory. This is bc the measles virus specifically attacks immune memory cells via attachment to CD150 - a protein enriched on memory cells.

3/

nature.com/articles/ni010…

3/
Read 10 tweets

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