Why Antibody Testing for Coronavirus is Important
Worldwide, the diagnosis of COVID-19 is based on the detection of the viral genetic material (RNA) of SARS-CoV-19 in respiratory samples from suspected patients, the method used is called PCR (Polymeric Chain Reaction). PCR is a diagnostic technique that has high sensitivity and specificity used for several years in the diagnosis of various infectious diseases. For these reasons, PCR is currently the diagnostic method of choice.
Carrying out such a large number of tests implies the need to continuously supply not only the PCR kits, but many other necessary materials such as swabs and transport means for sampling, inactivation solutions, extraction reagents and different types of plastic material. Analytical determinations with PCR must always be carried out by experienced personnel and usually take several hours to provide results.
Although PCR is the method of choice, it is also necessary to have rapid, simple tests, with high sensitivity and precision, and which can be carried out on a large scale. The objective is an early diagnosis, for better management (isolation and treatment if necessary) and patient monitoring, the application of prevention and control measures for expansion, and epidemiological surveillance.
The use of rapid immunological tests increases the diagnostic capabilities of the National Health System. These tests are easy to interpret and the results can be obtained in approximately 15 minutes.
Related Video: The Future of Coronavirus & The Impact of Antibody Tests with Steven Paletz, candidate for the congress representing Colorado’s district 6.
PCR vs Rapid Tests
The PCR is a type of diagnostic test that have been used for years in different public health crises related to infectious diseases. The PCR test allows detecting a fragment of the genetic material of a pathogen or microorganism.
The samples used come from respiratory secretions of people suspected of being infected, if the test detects viral RNA, the result is positive. Thus, it would be known that the patient has Covid-19. If the test is negative and the genetic material of the virus is not detected, the person would not be infected. In cases of negative results and high clinical suspicion, the test should be repeated. In this way it is corroborated that the patient is not infected.
Carrying out PCR tests has a high degree of complexity and requires the participation of trained personnel for its correct preparation. PCRs have three basic characteristics:
It has 99% specificity, which allows differentiating between two very close evolutionary microorganisms.
It has 96-98% sensitivity, it can detect 20 copies/ml of viral genetic material.
It allows detecting the virus in early stages when it is found in respiratory secretions.
“Rapid diagnostic immunological tests allow knowing in 10 or 15 minutes if a person is infected or not. For their part, PCRs can take several hours.”
Understanding the (Spike) Proteins
Despite the efficacy of this technique that has been used since the start of the coronavirus outbreak, the need to include a faster diagnosis due to the spread of the virus and the grate number of people affected arises. This is why immunological tests emerged.
Rapid diagnostic immunological tests allow knowing in 10 or 15 minutes if a person is infected or not. For their part, PCRs can take several hours.
Antibody tests are different because they require some knowledge of viral proteins, specifically, those proteins that the immune system responds to by triggering the production of antibodies that neutralize the virus.
The so-called spike protein is the main antigen that produces neutralizing antibodies, since this protein is responsible for the entry of the virus into the host cell. Research on the spike protein has also made progress in the development of therapies against Covid-19.
Several studies have shown that the production of antibodies against SARS-CoV-19 begins to take place from the 6th day of the onset of symptoms, simultaneously a decrease in viral load is observed. At 7 days half of the patients have total antibodies and at 15 days 100% of the patients have antibodies. This applies in both mild and severe cases.
According to the WHO, after infection IgM-type antibodies are generated and although they appear to begin to rise approximately 5-7 days after infection, tests detect them better at 8-14 days. After 15-21 days the IgG type antibodies appear.
Based on this, the immunological tests identify the presence of active disease since it allows evaluating the immune response of the patients which intensifies as the infection progresses. It is important to note that the presence of antibodies does not exclude the possibility of a person still being a transmitter of the virus.
Rapid immunological tests detect IgM and IgG antibodies and have a sensitivity of 89% and specificity of 91%. Although the protein used is specific for SARS-CoV-19, it cannot be ruled out that they give false positives in the presence of antibodies formed against other respiratory viruses such as SARS-CoV 1, which caused an epidemic in 2002, and other classes of coronaviruses.
The test results can be interpreted as follows:
No infection or very early phase infection: IgM (-) IgG (-)
Acute infection: IgM (+) IgG (-)
Prolonged acute infection IgM (+) IgG (+)
Past infection IgM (-) IgG (+)
Scope of Application and Performance of the Rapid Antibody Detection Test
Hospital Setting
It is indicated in patients with symptoms suggestive of covid 19 who have not undergone a PCR test or with negative PCR of several days of evolution:
If positive, diagnosis is confirmed (recent or past infection)
If negative, PCR will be done.
In hospitals, the strategy for taking and analyzing samples must follow the procedures established by their management.
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Out-of-Hospital Setting
The use of the tests in nursing homes and socio-health centers will be prioritized with the aim of making an early diagnosis and timely treatment.
In nursing homes and socio-sanitary centers, its use is indicated in patients who have symptoms of several days of evolution and the use of lancet is prioritized.
If more than one case with compatible symptoms of COVID-19 has been detected in the institution, it is not necessary to obtain a positive result in all suspected cases. If the presence of at least one case of Covid-19 is confirmed, the other patients with symptoms suggestive of the disease are considered positive considering that there is an outbreak in the institution. In these cases, symptomatic patients will be treated and isolated, and the other residents of the institution will be considered close contacts and will have to be quarantined. The sampling and analysis will be carried out in the residence or socio-health center.
Is Coronavirus Reinfection Possible?
The spike protein is the only viral protein responsible for entry into the host cell, its stability (poor mutation capacity) as SARS-CoV-19 evolves makes reinfection unlikely.
Virologists argue that reports of reinfection with SARS-CoV-19 are likely due to erroneous PCR testing. Once people make antibodies against a particular coronavirus, they probably have lifelong immunity. In fact, a study was conducted to determine how long immunity against the SARS-CoV 1 respiratory syndrome coronavirus lasts. It was discovered that 17 years later, the patients who presented the disease still had neutralizing antibodies against the virus.
The Importance of Antibody Tests
Immunological tests represent great advantage in the current situation since they allow establishing a rapid diagnosis. In addition, they can be performed at the home of suspected patients, preventing them from going to health centers. Although the test should always be under the supervision of a healthcare professional, they do not help saturate hospitals.
In addition to speeding up the diagnosis of suspected patients, immunological tests make it possible to verify that vaccines work as expected during clinical trials. By knowing the levels of antibodies in infected and recovered patients, scientists will have an understanding of the levels of protective antibodies that a vaccine must generate to produce effective immunity.
On the other hand, it can show that a healthcare professional has already had Covid-19 and is, therefore, likely to be immune, thus being able to return to work without fear of infection. That's something you can easily do with an antibody screening test and not with PCR.
Thanks to these rapid tools, it will be possible to improve screening in the population and limit the PCR assays only to those patients with symptoms that give a negative result to the rapid tests. This will free up professionals and resources in the National Health System.
Sources
1. Laboratory testing for 2019 novel coronavirus (2019-nCoV) in suspected human cases. Interim guidance. 19 March 2020. https://www.who.int/publications-detail/laboratory-testing-for-2019-novel-coronavirus-in-suspected-human-cases-20200117. Consultado 31 marzo 2020.
2. Wang W, Xu Y, Gao R, et al. Detection of SARS-CoV-2 in Different Types of Clinical Specimens. JAMA. Published online March 11, 2020. doi:10.1001/jama.2020.3786.
3. Interim Guidelines for Collecting, Handling, and Testing Clinical Specimens from Persons for Coronavirus Disease 2019 (COVID-19) https://www.cdc.gov/coronavirus/2019-nCoV/lab/guidelines-clinical-specimens.html. Consultado 28 Marzo 2020.
4. World Health Organization (2020) Novel Coronavirus (2019-nCoV) technical guidance: Laboratory testing for 2019-nCoV in humans. 31 Jan 2020. Available at: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/technicalguidance/laboratory-guidance. Consultado 26 Marzo 2020.
5. Zou L et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. N Engl J Med. 2020;382(12):1177–9.