ELISA tests at Icahn School of Medicine contradict earlier studies which found that antibodies developed to combat the SARS-CoV-2 coronavirus are short-lived
Medical laboratories at the forefront of the COVID-19 pandemic will be intrigued to learn that antibodies produced by the body to combat the coronavirus infection may actually provide long-term immunity, contrary to previous studies that found otherwise.
A recent study from the Icahn School of Medicine at Mount Sinai found that the protection may be more robust than previously believed. This may surprise many clinical laboratory scientists and clinical pathologists. Since the outbreak of the pandemic, multiple studies have been published with conflicting findings about the strength of the immune response to SARS-CoV-2 and the length of immunity provided after an infection.
In a Mount Sinai news release, however, Florian Krammer, PhD, microbiologist and Professor of Vaccinology in the Department of Microbiology at the Icahn School of Medicine at Mount Sinai, and a senior author of the paper, said, “While some reports have come out saying antibodies to this virus go away quickly, we have found just the opposite—that more than 90% of people who were mildly or moderately ill produce an antibody response strong enough to neutralize the virus, and the response is maintained for many months.”
The researchers published the findings of their study—which was based on an internally-developed antibody test—in Science.
The study concludes, “Although this cannot provide conclusive evidence that these antibody responses protect from reinfection, we believe it is very likely that they will decrease the odds ratio of reinfection and may attenuate disease in the case of breakthrough infection. We believe it is imperative to swiftly perform studies to investigate and establish a correlate of protection from infection with SARS-CoV-2.”
Florian Krammer, PhD (above), runs the Krammer Laboratory in the Department of Microbiology at the Icahn School of Medicine at Mount Sinai in New York. He noted that the longevity and neutralizing effects of antibody response are “critically important to enabling us to effectively monitor seroprevalence in communities, and to determining the duration and levels of antibody that protect us from reinfection.” Antibody response, he added, is also “essential for effective vaccine development.” (Photo copyright: Icahn School of Medicine at Mount Sinai.)
Details of the Icahn School of Medicine Study
The study arose from an effort by Mount Sinai to identify potential donors for a convalescent plasma therapy program. Beginning in late March, the health system used an enzyme-linked immunosorbent assay (ELISA) to screen thousands of individuals for presence of antibodies to the spike protein in the SARS-CoV-2 virus. The virus uses the spike protein to bind to a receptor in host cells, the researchers noted, making it “the main, and potentially only target for neutralizing antibodies.”
Screened patients either had confirmed cases of COVID-19, as determined by a polymerase chain reaction (PCR) test, or suspected cases, “defined as being told by a physician that symptoms may be related to SARS-CoV-2 or exposure to someone with confirmed SARS-CoV-2 infection,” the researchers wrote. The Mount Sinai health system also offered the test to employees.
Samples from each person were diluted in five discrete titers (concentrations) ranging from 1:80 to 1:2880, and each was tested for detectable presence of the antibodies. This allowed the researchers to categorize the samples as low, moderate, or high:
Low titers: 1:80 or 1:160
Moderate titers: 1:320
High titers: 1:960 or >1:2880
Between the start of the program and early October, the health system screened 72,401 people, of whom 30,082 tested positive for at least the lowest levels of antibodies. Among those who tested positive, a large majority fell into the moderate or high categories:
1:80: 690 (2.29%)
1:160: 1453 (4.83%)
1:320: 6765 (22.49%)
1:960: 9564 (31.79%)
1:2880: 11610 (38.60%)
The researchers also wanted to see whether the antibodies offered actual protection against the virus. So, they selected 120 samples and ran a quantitative microneutralization assay. In the lowest of the three categories, 50% of the samples showed neutralizing activity. That rose to 90% in the moderate category and 100% in the high category.
Finally, to determine how long protection might last, the researchers recalled 121 plasma donors for additional tests at two different points during the study. The researchers reported a slight drop in antibody levels about three months after onset of symptoms, and then a larger drop after five months. But antibodies were still present in most samples.
“It is still unclear if infection with SARS-CoV-2 in humans protects from reinfection and for how long,” the researchers wrote. “We know from work with common human coronaviruses that neutralizing antibodies are induced, and these antibodies can last for years and provide protection from reinfection or attenuate disease, even if individuals get reinfected.”
Previous ‘Conflicting’ Research
As previously noted, other studies raised doubts about the longevity of the antibodies produced by the body’s immune system. For example, the Mount Sinai researchers cited a study from China published in Nature Medicine that looked at the immune responses of 37 symptomatic patients and an equal number of asymptomatic individuals with laboratory-confirmed cases of the COVID-19 disease. In the latter group, 40% had no detectable levels of IgG antibodies after eight weeks.
The study also found a decrease in neutralizing antibodies in 30 of the asymptomatic individuals (81.1%) and 23 of the symptomatic individuals (62.2%) over the same period.
However, the Mount Sinai researchers pointed out that the antibody test in the Chinese study targeted a different protein. “The same paper also reported relatively stable (slightly declining) neutralizing antibody titers, which shows much higher concordance with our present findings,” they wrote. “Thus, the stability of the antibody response over time may also depend on the target antigen.”
A different study from England saw a 26% decline in antibodies over three months, CNN reported. That study, conducted by Imperial College London and Ipsos MORI, a market research firm, was based on responses from more than 365,000 randomly selected people who had self-administered a lateral flow antibody test.
But the seemingly conflicting studies from New York and the UK may not be contradictory, CNN reported. “People’s bodies produce an army of immune compounds in response to an infection and some are overwhelming at first, dying off quickly, while others build up more slowly. Measurements that show a waning antibody response in the first months after infection might be measuring this first wave—but there’s a second team building its forces in the background.”
In the same CNN report, Ania Wajnberg, MD, Director of Clinical Antibody Testing at Mount Sinai Hospital and co-author of the Icahn Mount Sinai study, said, “The serum antibody titer we measured in individuals initially were likely produced by plasmablasts—cells that act as first responders to an invading virus and come together to produce initial bouts of antibodies whose strength soon wanes.”
She added, “The sustained antibody levels that we subsequently observed are likely produced by long-lived plasma cells in the bone marrow. This is similar to what we see in other viruses and likely means they are here to stay. We will continue to follow this group over time to see if these levels remain stable as we suspect and hope they will.”
Does this mean that most people who get infected with the COVID-19 coronavirus will retain an immunity to the disease? Maybe. In the Icahn Mount Sanai study, Florian Kramer wrote, “More than 90% of people who were mildly or moderately ill produce an antibody response strong enough to neutralize the virus, and the response is maintained for many months.”
Thus, clinical laboratories engaged in serological testing may be asked to perform follow-up antibody tests to see if we do indeed create long-term immunity to COVID-19. Further, pathologists and medical laboratory scientists will want to follow future studies published in peer-reviewed journals to see if the findings of the Mount Sinai study are replicated at other sites.
It can take up to eight days after onset of symptoms for a person’s immune system to develop antibodies, so serological tests are not designed for diagnosing recent or active infections, stated a Mayo Clinic news story. However, Reuters reported that the availability of serological tests is “a potential game changer” because they could identify people who are immune even if they had no symptoms or only mild symptoms.
“Ultimately, this might help us figure out who can get the country back to normal,” Florian Krammer, PhD, told Reuters. Krammer’s lab at the Icahn School of Medicine at Mount Sinai in New York City has developed a serological test. “People who are immune could be the first people to go back to normal life and start everything up again,” he said.
However, some experts advise that the presence of antibodies is not necessarily a “get out of jail free” card when it comes to the coronavirus. “Infectious disease experts say immunity against COVID-19 may last for several months and perhaps a year or more based on their studies of other coronaviruses, including Severe Acute Respiratory Syndrome (SARS), which emerged in 2003,” reported Reuters. “But [the experts] caution that there is no way to know precisely how long immunity would last with COVID-19, and it may vary person to person.”
Additionally, it is also “uncertain whether antibodies would be sufficient protection if a person were to be re-exposed to the virus in very large amounts,” such as in an emergency room or ICU, Reuters reported.
Serological Survey Studies Get Underway Worldwide
Aside from detecting potential immunity, the World Health Organization (WHO) says serological tests could be useful for widespread disease surveillance and epidemiological research.
In the US, the Vitalant
Research Institute is leading several large serological survey or
“serosurvey” studies in which regional blood centers save samples of donated
blood for antibody testing, Science
reported.
Science also reported on a similar WHO initiative in which six countries will pool data from their own antibody studies. And in the Netherlands, blood banks have begun screening thousands of blood donations for presence of antibodies, Wired reported.
FDA Emergency Use Authorization
On March 16, the federal Food and Drug Administration (FDA) announced that it would allow commercial development and distribution of serological tests that “identify antibodies (e.g., IgM, IgG) to SARS-CoV-2 from clinical specimens” without an Emergency Use Authorization (EUA). The agency noted that these tests are “less complex than molecular tests” used to detect active infections, and that the policy change is limited to such testing in medical laboratories or by healthcare workers at the point-of-care. “This policy does not apply to at home testing,” the FDA reiterated.
“Serological tests can play a critical role in the fight against COVID-19 by helping healthcare professionals to identify individuals who have overcome an infection in the past and have developed an immune response,” said FDA Commissioner Stephen M. Hahn, MD (above with President Trump during a Coronavirus Task Force press briefing), in an April 7 press statement. “In the future, this may potentially be used to help determine—together with other clinical data—that such individuals are no longer susceptible to infection and can return to work. 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.” (Photo copyright: CNBC.)
FDA Issues First EUA for Rapid Diagnostic Test
Cellex Inc., based in Research Triangle Park, N.C., received the first EUA for its qSARS-CoV-2 serological test on April 1. As with other rapid diagnostic tests (RDTs) under development, the qSARS-CoV-2 test detects the presence of immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies in human blood. The biotechnology company’s RDT can be used to test serum, plasma, or whole-blood specimens, stated Cellex, and can produce results in 15 to 20 minutes.
The FDA has authorized use of the antibody test only by laboratories certified under CLIA to perform moderate and high complexity tests. Cellex has set up a COVID-19 website with information about the qSARS-CoV-2 test for clinical laboratories, patients, and healthcare providers.
Other Serological Tests Under Development
Mayo
Clinic Laboratories announced on April 13 that it is ramping up
availability of an internally-developed serological test. “Initial capacity
will be 8,000 tests per day performed at laboratory locations across Mayo Clinic,” stated the announcement.
“Testing will be performed 24 hours a day, and Mayo Clinic Laboratories is working
to ensure turnaround time is as close as possible to 24 hours after receipt of
the sample.”
Emory University in Atlanta announced on April 13 that it will begin deploying its own internally developed antibody test. Initially, testing will be limited to 300 people per day, comprised of Emory Healthcare patients, providers, and staff members. Eventually, testing will be “expanded significantly,” said Emory, with a goal of 5,000 tests per day by mid-June.
RDTs are typically qualitative, meaning they produce a
positive or negative result, stated the Center for Health Security. An ELISA
test “can be qualitative or quantitative,” noted the Center, but it can take
one to five hours to produce results.
A third type of serological test—the neutralization assay—involves infecting a patient’s blood with live coronavirus to determine if antibodies exist that can inhibit growth of the virus. The test takes three to five days in a level 3 biosafety laboratory to produce results. The Straits Times reported on one laboratory in Singapore that developed a neutralization assay to trace the source of COVID-19 infections that originated in Wuhan, China.
Serological testing is another important tool clinical
laboratories and epidemiologists can use to fight and ultimately defeat the
COVID-19 pandemic and is worth watching.
