Thread by @Craig_A_Spencer

🖍️ & 🥃 Episode 3: TESTING (part 2)

Today we tackle SEROLOGY (blood) testing - this type of testing is primarily used to determine evidence of PREVIOUS #COVID19 infection.

If you want to know more about viral testing (for current infection), check out yesterday's thread 👇

https://twitter.com/Craig_A_Spencer/status/1256750531437002752

Serology testing is used to detect the presence of antibodies in the bloodstream.

Antibodies (Ab) are proteins the body produces when it sees foreign material ('antigen')

They can then help the immune system neutralize and/or destroy invading viruses and bacteria.

There are 2 main types of antibodies (IgG and IgM) we look for. Their presence is evidence of previous infection.

For now, antibodies are only found in individuals who have had COVID.

This is true for patients who experienced symptoms as well as those who were asymptomatic.

This is important because many people who had COVID didn’t have symptoms & didn’t know it.

The hope is we'll produce a vaccine that will allow individuals to generate antibodies without being infected by the actual virus itself, like with other vaccines (measles, rubella etc.)

Most patients develop COVID antibodies about 10–11 days after infection. Currently we don't know how long they last for, since some decrease over time.

But antibodies for other diseases like chickenpox and measles can last decades!

Usually when people have antibodies, they are considered 'immune'.

With SARS-CoV-2 (the virus that causes COVID19), we still don't know for sure, and it might be a bit more complicated, as we will discuss later.

But first, let’s talk about antibody tests.

ANTIBODY TESTS

We have tests that can measure antibodies, but like any tests, they have flaws as well.

Like we discussed yesterday, they also have inherent limitations around sensitivity and specificity.

Need a refresher? Check the pics!

There are two types of antibody tests:

- Tests done in labs (ELISA) that measure amounts of Ab (quantitative);

- Commercial tests that are QUALITATIVE (think yes/no results, like pregnancy tests).

We will talk here about the commercial tests.

Photo: COVID-19 Testing Project

COMMERCIAL ANTIBODY TESTS:

To start with, these are exempt from FDA-approval. This was meant to get tests on the market quick. But it has huge implications:

- Will some be pretty good & reliable? Yeah.

- Will some be shoddy garbage with lots of incorrect results? Very yeah ☹️

There's a lot of reasons outside 'how good' the tests are that they may not tell us the 'right' answer:

- Tested too early in the disease process (it takes ~10 days before Ab appear)

- Test wasn't performed correctly;

- The levels of antibody dipped below the test's threshold.

More importantly, for many of these tests, we don't know how accurate they are.

Thankfully the team at COVD-19 Testing Project did the research for us (for more see this @nytimes piece by @apoorva_nyc).

In sum: “A few worked as advertised. Most did not.”
nyti.ms/2SvRYRr

Of the 14 antibody tests they looked at, only 1 didn't report a false positive!

Remember, false-positives are when the test says you HAVE antibodies when you actually DO NOT.

This is dangerous, because people will think they've already been infected and have antibodies.

Some of these tests had incredibly high false-positive rates (falsely telling MANY people they had Ab).

It's very possible that if we did Ab testing for everyone in the US, the # of false-positives could be higher than the # of true positives (the people who actually had COVID)!

And most importantly, EVEN IF someone has antibodies, we don't know exactly what that means!

With some viruses, if someone is infected once and develops antibodies, they are protected for life.

We aren't certain for the virus that causes COVID19, but it's likely MUCH shorter!

One study for SARS-CoV (a very similar virus) showed antibodies and likely immunity for up to 2 years.

And for MERS (another similar virus), it was closer to 3 years.

But again, with SARS-CoV-2, we just don't know.

(Want more?👇 article from @mlipsitch) nyti.ms/35spgpT

That's why 'immunity certificates' might not be as helpful as many hoped. And also why organizations like the @WHO recommend against them.

bit.ly/3dghfab

Also, NYC’s Health Dept recently sent out guidance saying ‘given the current lack of evidence that detection of SARS-CoV-2 antibody on serologic test is indicative of durable immunity, it SHOULD NOT be used for that purpose’.

One really important use of antibody testing will be identifying people who survived COVID and who can donate blood plasma. This is being evaluated as a potential COVID19 treatment. But this will rely more on the better, more reliable lab tests.

More on that in a few days! 😉

And that's all on serology testing!

Thanks to everyone who asked questions about testing, including @erlife13 @donaldverger @beckybpilars12 @elizabe07688985 @sarahtonin1988 @kate_krat @lorenzog4545 @rknecho @voteinpeace @cuzzortdonna @jennifer_greenb @mary_ellenO @TencomLtd

In our next episode, we’ll tackle pathophysiology!

This thread (and future ones) + all supporting articles & research area also at: bit.ly/3bRycHQ

A huge thanks to @TylerWen & @saurabhsudesh for helping put this together! And to @Brief_19 for our budding collaboration!

And as a reminder, the goal is to share something like this every night for a week at ~9pm to address big questions around testing, treatments, vaccines, pathophysiology and more!

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Be safe!