Thread by @DrEricDing

HUGE. **Rapid** 15 min tests approved by @WHO—a bold & right step for #COVID19. Akin to home pregnancy tests, rapid antigen tests better than PCR where labs scares & lag is long. Rapid tests are cheap & identifies *infectious* cases & fast isolation. Game changer for pandemic! 🧵

2) Rapid antigen testing is described as “The plan that could give our lives back”. Leading advocate is Harvard epidemiologist Dr Michael Mina @michaelmina_lab. He believes if we need to deploy millions of antigen tests to epidemic hotspots.

theatlantic.com/health/archive…

3) For those needing a background, unlike PCR tests which tests for the RNA genome of the coronavirus, the antigen tests for protein parts of the virus. PCR slightly more sensitive but PCR often finds RNA 🧬 fragments of non infectious virus pieces even when later can’t transmit.

4) But advantage of antigen test is not only is it fast (<15 min) and cheap ($5 or less, hopefully $1 when mass produced), and not require delicate logistics of sending to a lab and waiting for days or even a week... but think of use by masses and resource limited settings.

5) Currently, WHO only approved for low and middle income countries where resource low. And US FDA has only approved Abbott’s BINAXNOW via an EUA. Weird thing is HHS bought up all 150 mil rapid antigen tests—for entire 2020. But very unclear deployment. hhs.gov/about/news/202…

6) The other odd thing is that FDA’s EUA approval for antigen test BINAXNOW is only for symptomatic. But HHS Asst Sec Brett Grior also endorses using it “off label” for asymptomatic as well. I don’t disagree per se, but it’s ironic HHS asst sec goes around FDA’s EUA intent. 🤷🏻‍♂️

7) To be clear, people without symptoms of #COVID19 often have similar viral loads as symptomatic people, and both can be infectious. That’s why @michaelmina_lab endorses using antigen tests for ‘screening’ as well for testing anytime—not just diagnosing overtly sick patients.

8) That said, “clear evidence that “Abott didn’t just have symptomatic diagnostics in mind here, but also screening of asymptomatic people.” Symptomatic people are much more likely to have the virus, decreasing the chance of a false positive...”

9) “... For asymptomatic people, even in an area with lots of infections, Andersen worried that Abbott’s test isn’t accurate enough, and would generate many false positives.” theatlantic.com/science/archiv…

10) But there are “solutions to increase specificity. For example, a future version of the test could look for two viral targets. Or two tests could be packaged together, one of which would be a slightly more expensive test that you’d take if you got a positive on the first.”

11) Dr @michaelmina_lab calls this multi test confirmatory approach “orthogonal” testing—using a PCR test as followup or even a DIFFERENT antigen test (yes, you can test for different antigens to the virus—lots of possible targets on a virus). Akin to an independent verification.

12) An analogy—think of it this way, if we want to find a hidden enemy submarine, is it better to drop one sonar buoy (PCR test) every 100 miles that reports weekly, or drop a 90%-as-good sonar buoy every mile that reports every 15 min? Latter of course. That’s antigen testing!

13) Besides WHO, airlines like @lufthansa has gotten into the rapid antigen test game, offering tests for passengers starting October. But at first for First/Business class passengers—which is SUPER LAME and nonsensical. If limited, it should be randomly or for economy pax first!

14) BOTTOMLINE: the era of rapid cheap antigen testing is soon upon us, which would radically change the pandemic response and allow us to quickly isolate the sick and stop community transmission faster. But we need more/faster—& for FDA to approve antigen tests for ‘screening’.

15) Clarification about the other Abbot “rapid” test ID NOW touted in spring— a quicker PCR test but not cheap & it still needs a machine & lots of reagent cartridges, & not as accurate as other PCRs. The new rapid antigen lateral flow tests are akin to home pregnancy test.

16) UPDATE—The @WHO is in fact providing ***120 million*** such rapid antigen tests to low/middle income countries to fight #COVID19! Such a great move for these countries that don’t have enough lab resources and HC infrastructure. Bravo.

17) Further: In areas with little or no access to PCR tests, @mvankerkhove says rapid #COVID19 antigen tests can help:

📌Respond to suspected outbreaks in remote settings

📌Support cluster investigations around 1 case detected w/ PCR

📌Monitor trends in high-risk populations

18) Dr @mvankerkhove points out further details on the WHO guidance. Notably WHO issued the guidance recommendations for rapid antigen testing on September 11th, over 3 weeks ago! apps.who.int/iris/bitstream…

19) The sensitivity of the rapid antigen test varies between 70%-90% in different WHO modeled scenarios. But @michaelmina_lab points out that antigen identifies intact proteins of virus, instead of virus RNA fragments. And even if miss, rapid antigen tests can be repeated daily.

20) Antigen tests do “perform best in areas of active transmission and when collected from a case when they have their highest viral loads: -2 days before & up to 5-7 days after symptom onset” says @mvankerkhove, assuming symptoms at all. Many asymptomatic have similar loads too.

21) Here again, the above submarine-hunting sonar analogy comes back - even if 70-90% imperfect, it’s better to have more rapid daily tests (dense & fast sonar buoys) reporting rapidly on the spot than a slow cumbersome PCR tests done infrequently and reporting very slowly.

22) And while false positives are low at 1-2%, it’s not super low. Hence why @michaelmina_lab suggest the multi testing “orthogonal” tests & use in outbreak hotspots.

Altogether, the rapid testing allows for ➡️ rapid isolation ==> faster control of spread, even if imperfect.

23) Trump WH today just made a very misleading and flimsy announcement about BinaxNOW rapid antigen testing. Bottom line: their plan and test volume is a JOKE!!