Use and Interpretation of RATs

[wathe]

A new academic paper on use and interpretation of RATs for covid, from NEJM:

Rapid Diagnostic Testing for SARS-CoV-2

It's a nice summary, with a review of the science, a review of various guidelines, and some recommendations for best use.

And a very nice figure:

 

Edited January 22, 2022 by wathe

[KSera]

It looks like the data is pre-omicron? It seems to me, anecdotally, like PCRs are not as reliable early in omicron as they were with previous variants. Seen too many people who are symptomatic but with negative PCR, but then positive PCR a few days later. I wonder if that differs based on vaccination status and of those people who are symptomatic but not yet positive aren’t contagious either. Seems likely, if they don’t even have enough viral load to get a positive PCR. 

[wathe]

53 minutes ago, KSera said:

It looks like the data is pre-omicron? It seems to me, anecdotally, like PCRs are not as reliable early in omicron as they were with previous variants. Seen too many people who are symptomatic but with negative PCR, but then positive PCR a few days later. I wonder if that differs based on vaccination status and of those people who are symptomatic but not yet positive aren’t contagious either. Seems likely, if they don’t even have enough viral load to get a positive PCR. 

Yes, I think so. to the bolded.

 

 

[wintermom]

It does seem very much pre-omicron. The reality of testing in my city is more about whether you can even get your hands on any test rather than which test is best.

Now that omicron has ripped through the world, and so many people have had Covid, I'd love to see more information on the likelihood of contracting the virus again. 

Is there any data on the length of "protection" you have once you've had the virus. If it's not too much to ask, how about the protection you might have across different variants. Thanks!

Edited January 23, 2022 by wintermom

[KSera]

12 minutes ago, wintermom said:

Now that omicron has ripped through the world, and so many people have had Covid, I'd to see more information on the likelihood of contracting the virus again. 

Is there any data on the length of "protection" you have once you've had the virus. If it's not too much to ask, how about the protection you might have across different variants. Thanks!

I've seen anywhere from 5-16 time increased likelihood of a covid reinfection vs a Delta reinfection. Have also seen that having had Delta provides only 19% protection from getting omicron (I'm sure the number varies across studies, but they've all been low). Somewhat oddly, while Delta doesn't protect much against omicron, omicron provides more protection from Delta. That effect is much bigger for those with vaccine in addition to infection history vs those with infection alone.

Somewhere is a recent study with chart that shows different reinfection protection from one variant to the other. If I can find it, I'll come back and share.

[wathe]

47 minutes ago, wintermom said:

It does seem very much pre-omicron. The reality of testing in my city is more about whether you can even get your hands on any test rather than which test is best.

Now that omicron has ripped through the world, and so many people have had Covid, I'd to see more information on the likelihood of contracting the virus again. 

Is there any data on the length of "protection" you have once you've had the virus. If it's not too much to ask, how about the protection you might have across different variants. Thanks!

Wintermom, I hear you on testing access.  (Wintermom and I are in the same province, I think.   PCR tests are only available to those who meet certain select high risk criteria, meet certain select social criteria (ie live in a shelter, nursing home, or are incarcerated,) or fall into certain select occupational categories (ie patient-facing healthcare worker).  Otherwise, limited to RATs if you can source one - and they are as rare as hens teeth in the marketplace.  Most people simply don't have the option to test.)

Regarding how long protection lasts from Omicron, and how much protection it confers:  We're still in early days. There are studies, but the data is still a bit wobbly, I think. I haven't seen any that I would call robust.  Omicron was only first identified less than 2 months ago, after all.  And whether or not it will confer immunity against the next variant is anyone's guess.

As an aside, It's actually quite amazing to me how quickly the science has been moving throughout this pandemic.  I mean, I get that the pandemic feels like it's been going forever - but really 2 years is a very short time in medical research land.  We've learned an amazing amount, and accomplished an awful lot in those 2 years.

[wintermom]

10 hours ago, wathe said:

Wintermom, I hear you on testing access.  (Wintermom and I are in the same province, I think.   PCR tests are only available to those who meet certain select high risk criteria, meet certain select social criteria (ie live in a shelter, nursing home, or are incarcerated,) or fall into certain select occupational categories (ie patient-facing healthcare worker).  Otherwise, limited to RATs if you can source one - and they are as rare as hens teeth in the marketplace.  Most people simply don't have the option to test.)

Regarding how long protection lasts from Omicron, and how much protection it confers:  We're still in early days. There are studies, but the data is still a bit wobbly, I think. I haven't seen any that I would call robust.  Omicron was only first identified less than 2 months ago, after all.  And whether or not it will confer immunity against the next variant is anyone's guess.

As an aside, It's actually quite amazing to me how quickly the science has been moving throughout this pandemic.  I mean, I get that the pandemic feels like it's been going forever - but really 2 years is a very short time in medical research land.  We've learned an amazing amount, and accomplished an awful lot in those 2 years.

You're correct, we are in the same province and that's a great way to describe finding a rapid testing kit! There's not a lot of chicken teeth to be found. 😅 

 

[wathe]

News article on a study from Nova Scotia on increased sensitivity of combined throat/nasal swabs for RATs (news article, data not yet published).  Sensitivity of combined swab 88.7%, vs 64.5% for swab from nose or throat alone.  Also reporting that Nova Scotia Health now recommends swabbing both nose and throat for RATs (though I don't actually see that recommendation on NSH's official website yet)

Edited January 23, 2022 by wathe

[Halftime Hope]

3 minutes ago, wathe said:

Article on a study from Nova Scotia on increased sensitivity off combined throat/nasal swabs for RATs (news article, data not yet published).  Sensitivity of combined swab 88.7%, vs 64.5% for swab from nose or throat alone.  Also reporting that Nova Scotia Health now recommends swabbing both nose and throat for RATs (though I don't actually see that recommendation on NSH's official website yet)

This is good news; I hope the FDA/CDC look at this data. 

(ETA: a side note, for those in the US, we often see rapid antigen tests (RATs) referred to as LFTs, lateral flow tests, since most of what is available to the public are in that format, like the home pregnancy tests most of us are familiar with.) 

 

Edited January 23, 2022 by Halftime Hope

[wathe]

Preprint of the Canadian RAT study that found sensitivity of throat + nose > nose alone.

Also, ISNOT is a great acronym.  Nose swabs --> snot.  ha ha.

[wintermom]

1 hour ago, wathe said:

Preprint of the Canadian RAT study that found sensitivity of throat + nose > nose alone.

Also, ISNOT is a great acronym.  Nose swabs --> snot.  ha ha.

Some acronyms are superb! 

[KSera]

Now for something completely different....the following actually comes from BuzzFeed 😳😂. I saw it linked on medTwitter though and it has some good info on the use of rapid tests and why they may take awhile to show positive, and how that might differ for vaccinated vs unvaccinated. The people quoted as sources are legit.

If You Think You Have COVID But Your Rapid Test Is Negative, Here’s Why