COVID-19 tests: how they work, serological tests and immunity, how accurate are they?

[AussieNeil]

With many countries reducing restrictions implemented to slow the coronavirus pandemic, effective testing for an active COVID-19 infection or determining whether someone has (hopefully long lasting) immunity to this latest SARS virus, will become critical.

Here are a few references that explain how COVID-19 tests work, how the new serological (antibody blood tests) work and how accurate they are currently.

COVID-19 tests: how they work and what’s in development

There are two main ways to test for infection with SARS-CoV2 (the coronavirus that causes COVID-19 disease). The first is a very sensitive test that looks for the RNA of the virus using a technique called RT-PCR. A second type of test measures the antibody responses to virus in blood serum.

theconversation.com/covid-1...

Checking blood for coronavirus antibodies – 3 questions answered about serological tests and immunity

These tests look for antibodies that your body’s immune system generated to fight the infection. So, the tests detect the response to the virus, not the virus itself. They cannot be used early in infection, before a patient’s body has mounted an antibody response.

theconversation.com/checkin...

Coronavirus: how accurate are coronavirus tests? (False positives and negatives, with a great explanation of the impact of these on a real life example).

The meaning of a test result for an person depends not only on the accuracy of the test, but also on the estimated risk of disease before testing.

theconversation.com/coronav...

Why can’t we use antibody tests for diagnosing COVID-19 yet?

...it’s hard to make one that works. It’s difficult to craft a test that is specific enough to detect just SARS-CoV-2 (the virus that causes COVID-19), and not other similar viruses. More importantly for diagnosis of active cases, it’s difficult to craft a test that is sensitive enough to detect SARS-CoV-2 antibodies early on during infection.

theconversation.com/why-can...

Serology Tests in COVID-19: Are They Good Enough?

— Top official at major diagnostics company has questions

Shamiram R. Feinglass, MD, MPH, is chief medical officer at diagnostics maker Beckman Coulter, responding to the FDA policy adjustment last week on serology-based COVID-19 antibody testing.

Right now, we don't know the level of disease in our communities. We don't have enough data yet to determine if antibodies will give people immunity. We need to understand how to get people back to work safely and reopen our economy. In order to do that we need to test them. Before a vaccine is available, we need to decide how to decrease the public health risk. We have an urgent need for high quality tests capable of providing actionable results. We need a large amount of high-quality tests that we can process quickly that produce reliable results. These tests need to be available broadly. The right serology testing will help us find the answers we need to get us back to work, identify convalescent plasma, and develop a vaccine. It will be an important part of what helps us collectively to pull out of this crisis. It's going to take a lot of hard work to get us there. But we must stick to high standards for the good of global health.

medpagetoday.com/infectious...

Photo: Shuttercock image showing the Y shaped antibody proteins locking onto the spikes of a SARS-CoV-2 virus and targeting it for destruction by our immune system

This is an unlocked post, which can be returned in Internet searches: healthunlocked.com/cllsuppo...

Neil

[Ernest2]

Cool photo!

Ernest

[AussieNeil Partner Administrator]

The U.S. Centers for Disease Control and Prevention (CDC) plans a nationwide study of up to 325,000 people to track how the new coronavirus is spreading across the country into next year and beyond.

The CDC study, expected to launch in June or July, will test samples from blood donors in 25 metropolitan areas for antibodies created when the immune system fights the coronavirus, said Dr. Michael Busch, director of the nonprofit Vitalant Research Institute.

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The CDC-funded portion, to be formally announced this week, will expand the scope and time frame, taking samples over 18 months to see how antibodies evolve over time, said CDC spokeswoman Kristen Nordlund.

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Antibody studies, also known as seroprevalence research, are considered critical to understanding where an outbreak is spreading and can help guide decisions on restrictions needed to contain it.

The CDC study should also help scientists better understand whether the immune response to COVID wanes over time.

reuters.com/article/us-heal...

[AussieNeil Partner Administrator]

Ars Technica reports on the Korea Centers for Disease Control and Prevention's investigation and analysis of re-positive COVID-19 cases, dated 19 May 2020 (“Re-positive cases” are cases that test positive for SARS-CoV-2 after being discharged from isolation).

arstechnica.com/science/202...

People who recover from COVID-19 but test positive for the virus again days or weeks later are not shedding viral particles and are not infectious, according to data released Tuesday by the Korea Centers for Disease Control and Prevention. The so-called "re-positive" cases have raised fears that an infection with the new coronavirus, SARS-CoV-2, could "reactivate" in recovered patients or that recovering from the infection may fail to produce even short-lived immunity, allowing patients to immediately become re-infected if they are exposed. The new data from Korea should ease those concerns.

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The type of tests that suggested the 285 people were positive for COVID-19 a second time were what’s called RT-PCR tests (reverse transcription polymerase chain reaction). These tests are typically used to diagnose a COVID-19 infection. They do so by recognizing and making copies of unique, targeted fragments of SARS-CoV-2’s genetic material.

It’s a precise and effective way to determine if someone’s been infected with the virus. If someone has SARS-CoV-2 genetic material in their airways, they’ve been infected. That said, having genetic material doesn’t necessarily mean that the person still has an active infection and infectious viral particles. They may just have lingering fragments of genetic material from destroyed viral particles.

That appears to be the case here. When KCDC researchers tried to isolate and grow whole, infectious particles of SARS-CoV-2 from the 108 cases they were able to test—all 108 were negative for whole virus.

From the Korea Centers for Disease Control and Prevention's media release: cdc.go.kr/board/board.es?mi...

From the 285 re-positive cases, a total of 790 contacts were identified (351=family; 439=others). From the monitoring of contacts, as of now, no case has been found that was newly confirmed from exposure during re-positive period alone.

- Based on the findings, starting 0:00 of 19 May, KCDC has stopped applying the previous protocols for the management of confirmed cases after discharge from isolation and for the management of re-positive cases. Under the new protocols, no additional tests are required for cases that have been discharged from isolation.

- Reporting and investigation of re-positive cases and investigation of contacts of re-positive cases will be continued as before for the purposes of research and investigation. However, based on experts’ recommendations, the terminology for referring to such cases will be changed from “re-positive” to “PCR re-detected after discharge from isolation”. (My emphasis)

Neil

[AussieNeil Partner Administrator]

Determining the prevalence of anti-SARS-CoV-2 antibodies in a population, known as sero-surveillance, may provide a way to gain a more complete understanding of the progression of the COVID-19 epidemic.

As anti-SARS-CoV-2 antibodies only appear seven to 10 days after symptoms they are not suitable for clinical diagnosis.

However, as even mild and asymptomatic infections result in sero-conversion (this is the generation of detectable antibodies), serology is better able to provide an in-depth understanding of COVID-19 transmission, as well as a more accurate estimation of case fatality rates, and an assessment of population-level immunity.

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While antibody responses to an infection are long-lasting, antibody levels vary greatly over time. After a rapid rise, responses peak at two to four weeks after infection and then decay in two phases.

Firstly, they decay rapidly over the first three to four months. This is followed by a much slower decay over the following months and years. These changes over time mean that serological tests achieve their best sensitivity in the relatively short period of peak antibody levels, but have substantially lower performance several months after an infection.

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We are now applying the same design principals and technology to develop a high-performance assay for COVID-19 sero-surveillance. Our team has started to screen a large number of SARS-CoV-2 protein fragments to select the best performing antigens.

In a first pilot assay (or test) with four SARS-CoV-2 proteins, we were able to identify people with previously confirmed SARS-CoV-2 infections with a sensitivity of 96.4 per cent and a specificity of 99.1 per cent.

From Lessons from malaria sero-surveillance

thenewdaily.com.au/life/sci...