COVID-19 News: University of Pennsylvania Study Shows That Past Exposure To Seasonal Coronaviruses Does Not That Protect Against SARS-CoV-2
Contrary to past claims by so called ‘experts’, and also ‘findings’ from ‘half-baked’studies, a new study by researchers from Perelman School of Medicine at the University of Pennsylvania has found that past exposure to seasonal coronaviruses (CoVs), which cause the common cold, does not result in the production of antibodies that protect against the novel coronavirus SARS-CoV-2.
SARS-CoV-2 coronavirus has rapidly spread within the human population. Although SARS-CoV-2 is a novel coronavirus, most humans had been previously exposed to other antigenically distinct common seasonal human coronaviruses
(hCoVs) before the COVID-19 pandemic.
The study team quantified levels of SARS-CoV-2-reactive antibodies and hCoV-reactive antibodies in serum samples collected from 431 humans before the COVID-19 pandemic. The team then quantified pre-pandemic antibody levels in serum from a separate cohort of 251 individuals who became PCR-confirmed infected with SARS-CoV-2. Finally, the study team longitudinally measured hCoV and SARS-CoV-2 antibodies in the serum of hospitalized COVID-19 patients.
The study findings indicate that most individuals possessed hCoV-reactive antibodies before the COVID-19 pandemic. The team determined that ∼20% of these individuals possessed non-neutralizing antibodies that cross-reacted with SARS-CoV-2 spike and nucleocapsid proteins. These antibodies were not associated with protection against SARS-CoV-2 infections or hospitalizations, but they were boosted upon SARS-CoV-2 infection.
The study findings were published in the peer reviewed journal: Cell https://www.cell.com/cell/fulltext/S0092-8674(21)00160-4#%20
The study was led by led by Scott Hensley, PhD, an associate professor of Microbiology at the Perelman School of Medicine at the University of Pennsylvania.
Past ‘half-baked’ studies have suggested that recent exposure to seasonal CoVs protects against SARS-CoV-2, the virus that causes COVID-19.
The research from Dr Hensley's team however suggests that if there is such protection, it does not come from antibodies.
The study team found that many individuals possessed antibodies that could bind to SARS-CoV-2 before the pandemic, but these antibodies could not prevent infections.
Dr Hensley told Thailand Medical News, “Although antibodies from prior coronavirus infections cannot prevent SARS-CoV-2 infections, it is possible that pre-existing memory B cells and T cells could potentially provide some level of protection or at least reduce the disease severity of COVID-19. Studies need to be completed to test that hypothesis."
The study team examined blood samples banked before the pandemic from hundreds of people. They found that more than 20 percent of these pre-pandemic samples carried "cross reactive" anti-CoV antibodies that could bind not only to ordinary cold-causing CoVs but also to key sites on SARS-CoV-2.
But these cross-reactive antibodies could not neutralize the infectivity of SARS-CoV-2, and were not associated with better outcomes in people who later went on to get COVID-19.
The study team also found from blood testing in different groups that both children and adults on average tend to have similar levels of cross-reactive anti-CoV antibodies, implying that these antibodies are not the factor that confers protection against severe COVID-19 among most children.
The current COVID-19 pandemic, after more than a year of global spread, has resulted in more than 107 million reported infections, of which more than 2.35 million have been fatal.
Though some risk factors, such as age, are clear enough, scientists still don't fully understand why some people become deathly sick with COVID-19 while others escape with mild illness or even no symptoms.
Some have considered antibodies as a possible explanation. Ordinary seasonal coronaviruses, of the type that cause colds, have long circulated in the human population. An obvious hypothesis is that some of the antibodies elicited by these common infections cross-react with the novel coronavirus SARS-CoV-2, providing some measure of protection, at least against severe COVID-19 illness.
Interestingly in one set of analyses that Dr Hensley and colleagues conducted, they examined blood samples collected from 263 children at the Children's Hospital of Philadelphia, and from 168 adults at the Penn Medicine Biobank. The samples had been taken in 2017, more than two years before the SARS-CoV-2 pandemic started.
The study team found that most of the 431 samples contained antibodies to ordinary, seasonal CoVs. Some samples, about 20 percent, contained anti-CoV antibodies that were "cross reactive" with SARS-CoV-2, binding tightly to sites on its outer spike protein and/or its nucleocapsid protein ie the two coronavirus proteins that are most accessible to the immune system of infected hosts.
The study team separately analyzed blood samples banked before the pandemic from 251 people who later went on to test positive for SARS-CoV-2, and a control group of 251 people matched for age and other relevant characteristics who did not test positive for the novel coronavirus. Again, they found that greater than 20 percent of the pre-pandemic samples contained anti-CoV antibodies that could cross-react with the SARS-CoV-2 spike and/or nucleocapsid proteins.
Interestingly similar proportions of the infected and uninfected groups had these cross-reactive antibodies, implying that they provided no protection against SARS-CoV-2 infection.
Moreover, in the group that later went on to be infected with SARS-CoV-2, levels of cross-reactive anti-CoV antibodies in their pre-pandemic blood samples did not correlate with measures of COVID-19 severity such as the need for hospitalization or ICU care.
Also in a third set of tests, the researchers analyzed blood samples from 27 hospitalized COVID-19 patients, and found that levels of these cross-reactive anti-CoV antibodies were strongly boosted during the course of COVID-19 illness.
The study team recommends that larger studies be done to definitively resolve the question of whether pre-existing anti-CoV antibodies can protect against SARS-CoV-2 viruses.
The team also suggests that further studies examine other types of immune response, such as the T cell response, to see if these provide a measure of cross-reactive protection following seasonal CoV infection.
Importantly the team says their results suggest that the shared sites where some antibodies bind both to seasonal coronaviruses and to SARS-CoV-2 are generally not vulnerable sites where SARS-CoV-2 can be neutralized.
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