Much confusion about rapid antigen tests

ALL evidence - when evaluated appropriately! - shows these are VERY good at detecting infectious virus

• ~100% if used frequently

• >95% for single samples with high, most likely contagious viral loads

The tests work
We've been evaluating rapid Ag tests on campuses. We find these tests - when used as screening w/out symptoms DO miss most PCR positives!

BUT EXPECTED! - ALL misses were previously detected and already finished isolation.

Ag is MUCH more specific than PCR for contagious virus
this is the whole point of rapid antigen tests - they find people who are currently infectious. They are fast, give crucial immediate results and unlike PCR do NOT stay positive for weeks/months after someone is no longer infectious.
This is also at the center of why people keep confusing them as low sensitivity. They simply cannot be compared against PCR RNA positives. PCR RNA remains positive LONG after someone is infectious. Making PCR a poor tool for knowing who requires isolation.

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More from @michaelmina_lab

14 Jan
Will delaying #COVID19 vaccine doses cause vaccine immune escape?

This nice article misses an extremely important part - that unvaccinated ppl too have so called “partial immunity” while infected.

Escape from immunity isn’t same as from antibiotics

Unlike antibiotics where resistance happens w partial doses, to be a risk you also must be taking them in first place.

When considering escape from spike protein derived immunity - must consider everyone w/out sterilizing immunity at risk to induce a mutant upon infection.

Whether no vaccine or a single dose (or two) people create antibodies against the same part of the protein.

If discussing “partial immunity” or low affinity antibodies, must consider that a fully naive person might pose greater risk for escape than a single dose person

Read 11 tweets
12 Jan
Dear ⁦@guardian

This article is incomplete & represents a minority view of the science.

The experts here are gravely misinterpreting the data and sowing confusion among the masses.

The rapid tests are working well!

This coverage isn’t balanced…
The details are difficult to describe via Twitter but I’ve tried on many occasions. The described low accuracy is false. These tests are doing very well to catch infectious people. We do NOT want to detect and isolate people who are not infectious and just have old remnant RNA.
I know people want to hate on the government for purchasing tests - but the Innova test is working entirely as expected. Very good for detecting contagious people. Which is the only goal here.

I’d be happy to write an OpEd for @guardian to explain.
Read 4 tweets
10 Jan
UK Rolling out #COVID19 Rapid Tests!

**NOTE: A quote says rapid tests missed 60% of positives in Liverpool

NOT accurate


(PCR remains Positive for a long time, rapid Ag does not)…
Despite some poor messaging in UK - Rapid Ag tests work WELL to find CURRENTLY INFECTIOUS ppl

Frequent rapid Ag testing sensitivity is >95% to find infectious people.

(ppl get confused & say they're low sensitivity - but that's when compared to RNA on PCR from prior infection)
A major attribute of rapid Ag testing is they can be FREQUENT

It's not the sensitivity of a test to find virus particles that matters

It's the sensitivity of the testing program to find and isolate infectious people that matters.

For that, PCR often fails. Rapid Tests do well.
Read 6 tweets
9 Jan
Honestly @US_FDA @CDCgov

HOW have we FAILED to get frequent rapid testing out?!

•The science & plans are there

•All you've given is pushback

Almost 5 months ago I wrote:

"So we're not looking back 5 months from now wishing we acted"


@ASMicrobiology @APHL
I know @ASMicrobiology & @APHL you do not support these tests - pity

Confounding sensitivity & specificity for EFFECTIVENESS in midst of a pandemic is a dangerous and now deadly decision

(1) Define the use
(2) Then take a stance on test effectiveness

You never really did (1)
Here is a primer for what I'm referring to.

Read 4 tweets
8 Jan
#COVID19 is overlooked by the world as as urgent a crisis in Africa as every where else

We continue to make the same mistakes of confusing a lack of testing for a lack of cases.

In this study in Zambia, ~20% of deaths were found to be COVID related!

To determine this, the researchers performed a systematic analysis of swabbing and running PCR on post-mortem individuals.

These ppl would not have been detected/confirmed as having COVID otherwise and thus not officially reported owing to a lack of testing infrastructure

As @brookenichols has discussed, rapid Ag testing isnt only a powerful tool for frequent use to slow spread (as I’ve discussed) - it is also a powerful tool for less resourced countries to access and massively scale up testing to get formal estimates of transmission/cases

Read 6 tweets
4 Jan

On False POSITIVES of rapid antigen tests.

This 🧵 is on SPECIFICITY or the issues of False POSITIVES and rapid antigen tests.

Many people are concerned that these fast, inexpensive tests cause too many false positives and will overload PCR labs...

Rapid antigen tests can have 98%-99.9% specificity meaning between 0.1% and 2% of tests run might be falsely positive.

If prevalence is low, even a 99.9% specificity could mean many of the positive tests are falsely positive.

But w rapid tests, there are rapid solutions!

Many ppl instinctively worry that a false positive will mean an erroneous 10 day isolation and that huge numbers of people are going to require laboratory based PCR confirmation tests and this will overload the system.

No, this is stuck-in-our-ways thinking...

Read 14 tweets

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