Virus World

The blood from seriously ill Covid-19 patients on ventilators was found by researchers to be highly inflammatory and harmful to the body. Antibodies  generated by the immune system to neutralise 

Serology tests detect the presence of antibodies in the blood when the body is responding to a specific infection, like COVID-19. In other words, the tests detect the body’s immune response to the infection caused by the virus rather than detecting the virus itself. In the early days of an infection when the body’s immune response is still building, antibodies may not be detected.

This limits the test’s effectiveness for diagnosing COVID-19, and this is one reason serology tests should not be used as the sole basis to diagnose COVID-19. Serology tests could play a role in the fight against COVID-19 by helping healthcare professionals identify individuals have developed an immune response to SARS-CoV-2. In addition, these test results can aid in determining who may donate a part of their blood called convalescent plasma, which may serve as a possible treatment for those who are seriously ill from COVID-19. However, to use these test properly, it is important to understand their performance characteristics and limitations. Moreover, studies are underway to address questions that will better inform the appropriate use of these tests, such as whether the presence of antibodies conveys a level of immunity that would prevent or minimize the severity of re-infection as well as the duration for which immunity lasts.

The performance of these tests is described by their “sensitivity,” or their ability to identify those with antibodies to SARS-CoV-2 (true positive rate), and their “specificity,” or their ability to identify those without antibodies to SARS-CoV-2 (true negative rate). A test’s sensitivity can be estimated by determining whether or not it is able to detect antibodies in blood samples from patients who have been confirmed to have COVID-19 with a nucleic acid amplification test, or NAAT. In some validation studies of these tests, like the one FDA is conducting in partnership with NIH, CDC, and BARDA, the samples used, in addition to coming from patients confirmed to have COVID-19 by a NAAT, may also be confirmed to have antibodies present using other serology tests. A test’s specificity can be estimated by testing large numbers of samples collected and frozen before SARS-CoV-2 is known to have circulated to demonstrate that the test does not produce positive results in response to the presence of other causes of a respiratory infection, such as other coronaviruses....

Such a test may help scientists learn how widespread the infection is, and how long people remain immune after recovering. The Food and Drug Administration on Thursday approved a new test for coronavirus antibodies, the first for use in the United States. Currently available tests are designed to find fragments of viral genes indicating an ongoing infection. Doctors swab the nose and throat, and amplify any genetic material from the virus found there.

The new test, by contrast, looks for protective antibodies in a finger prick of blood. It tells doctors whether a patient has ever been exposed to the virus and now may have some immunity. That is important for several reasons. People with immunity might be able to venture safely from their homes and help shore up the work force. It may be particularly important for doctors and nurses to know whether they have antibodies. Antibody testing eventually should give scientists a better sense of how widespread the infection is in the population — and help researchers calculate more precisely the death rate.

“If we don’t know the asymptomatic or mild cases, we won’t know if it’s killing a sizable fraction of the people who have it, or only people who have underlying conditions or are very unlucky,” said Dr. Carl Bergstrom, an infectious diseases expert at the University of Washington in Seattle.  The new test, made by Cellex, looks for two types of antibodies: immunoglobulin M, made by the body a few days into an infection; and immunoglobulin G, made later but created specifically to neutralize a particular invader. The test delivers results in about 15 minutes. But just having antibodies does not guarantee immunity from the coronavirus.

FDA Approval Letter for Cellex Test (April 1, 2020): 

https://www.fda.gov/media/136622/download

Serological SARS-CoV-2 assays are needed to support clinical diagnosis and epidemiological investigations. Recently, assays for the large-volume detection of total antibodies (Ab) and immunoglobulin (Ig) G and M against SARS-CoV-2 antigens have been developed, but there are limited data on the diagnostic accuracy of these assays. This study was organized as a Danish national collaboration and included fifteen commercial and one in-house anti-SARS-CoV-2 assays in sixteen laboratories. Sensitivity was evaluated using 150 serum samples from individuals diagnosed with asymptomatic, mild or moderate nonhospitalized (n=129) or hospitalized (n=31) COVID-19, confirmed by nucleic acid amplification tests, collected 13-73 days from symptom onset. Specificity and cross-reactivity were evaluated in samples collected prior to the SARS-CoV-2 epidemic from > 586 blood donors and patients with autoimmune diseases or CMV or EBV infections. Predefined specificity criteria of ≥99% were met by all total-Ab and IgG assays except one (Diasorin/LiaisonXL-IgG 97.2%).

The sensitivities in descending order were: Wantai/ELISA total-Ab (96.7%), CUH/NOVO in-house ELISA total-Ab (96.0%), Ortho/Vitros total-Ab (95.3%), YHLO/iFlash-IgG (94.0%), Ortho/Vitros-IgG (93.3%), Siemens/Atellica total-Ab (93.2%), Roche-Elecsys total-Ab (92.7%), Abbott-Architect-IgG (90.0%), Abbott/Alinity-IgG (median 88.0%), Diasorin/LiaisonXL-IgG (84.6%), Siemens/Vista total-Ab (81.0%), Euroimmun/ELISA-IgG (78.0%), and Snibe/Maglumi-IgG (median 78.0%). The IgM results were variable, but one assay (Wantai/ELISA-IgM) had both high sensitivity (82.7%) and specificity (99%). The rate of seropositivity increased with time from symptom onset and symptom severity.

In conclusion, predefined sensitivity and specificity acceptance criteria of 90%/99%, respectively, for diagnostic use were met in five of six total-Ab and three of seven IgG assays.

Preprint of the study available at medRxiv (August 2, 2020):

https://doi.org/10.1101/2020.07.30.20165373

Humoral immunity in asymptomatic infections with SARS-CoV-2 has not been well established. 63 healthy contacts, 63 asymptomatic individuals, and 51 mild patients were enrolled in this study and screened using nucleic acid testing (NAT) and commercial kits of serum IgM and IgG antibodies against recombinant nucleoprotein (N) and spike (S) proteins of SARS-CoV-2. Asymptomatic and mild patients were classified into at least four types based on NAT and serological tests, especially 81% and 25.4% negative NAT but positive IgM/IgG responses, respectively. 

Antibody dynamics were further demonstrated by IgM and IgG profile responses to SARS-CoV-2 proteome. IgM antibody responses against S1 were elicited in asymptomatic individuals as early to the seventh day after exposure and peaked on days from 17d to 25d, which might be used as early diagnostic biomarkers. Moreover, asymptomatic individuals evoked weaker S1 specific IgM and neutralizing antibody responses than mild patients. Most importantly, S1 specific IgM/IgG responses and the titers of neutralizing antibody in asymptomatic individuals gradually vanished in two months. Our findings might have important implications for serological survey, public health and immunization strategy.

Preprint available at medRxiv (July 11, 2020):

https://doi.org/10.1101/2020.07.09.20149633

There’s been a lot of excitement about the potential of antibody-based blood tests, also known as serology tests, to help contain the coronavirus disease 2019 (COVID-19) pandemic. There’s also an awareness that more research is needed to determine when—or even if—people infected with SARS-CoV-2, the novel coronavirus that causes COVID-19, produce antibodies that may protect them from re-infection.

A recent study in Nature Medicine brings much-needed clarity, along with renewed enthusiasm, to efforts to develop and implement widescale antibody testing for SARS-CoV-2. Antibodies are blood proteins produced by the immune system to fight foreign invaders like viruses, and may help to ward off future attacks by those same invaders. In their study of blood drawn from 285 people hospitalized with severe COVID-19, researchers in China, led by Ai-Long Huang, Chongqing Medical University, found that all had developed SARS-CoV-2 specific antibodies within two to three weeks of their first symptoms. Although more follow-up work is needed to determine just how protective these antibodies are and for how long, these findings suggest that the immune systems of people who survive COVID-19 have been be primed to recognize SARS-CoV-2 and possibly thwart a second infection.

Specifically, the researchers determined that nearly all of the 285 patients studied produced a type of antibody called IgM, which is the first antibody that the body makes when fighting an infection. Though only about 40 percent produced IgM in the first week after onset of COVID-19, that number increased steadily to almost 95 percent two weeks later. Some of these patients also produced a type of antibody called IgG. While IgG often appears a little later after acute infection, it has the potential to confer sustained immunity. To confirm their results, the researchers turned to another group of 69 people diagnosed with COVID-19. The researchers collected blood samples from each person upon admission to the hospital and every three days thereafter until discharge. The team found that, with the exception of one woman and her daughter, the patients produced specific antibodies against SARS-CoV-2 within 20 days of their first symptoms of COVID-19.

Published in Nature Medicine:

https://doi.org/10.1038/s41591-020-0897-1