For months, scientists have wondered whether previous exposure to seasonal coronaviruses that cause common colds could prevent people from catching a serious case of COVID-19.
This protection would explain why children, who catch more colds, are less affected by SARS-CoV-2, the coronavirus that causes COVID-19. But a new study, published Tuesday (February 9) in the journal Cell, found that antibodies to these seasonal coronaviruses do not prevent SARS-CoV-2 infection or reduce the severity of the disease.
There are four coronavirus that circulate in the human population and cause symptoms of a common cold – and most people have been exposed to them several times in their lives (especially as children) and therefore developed antibodies against them. The researchers conducted a series of studies last year to find out whether these antibodies could also bind to SARS-CoV-2 and protect against infections or serious illnesses.
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“We found that many people had antibodies that could bind to SARS-CoV-2 before the pandemic, but these antibodies cannot prevent infections, ”senior author Scott Hensley, associate professor of microbiology at the University of Pennsylvania Perelman School of Medicine, said in a statement. Nor could antibodies prevent serious diseases.
This is a different conclusion from a similar study published in the journal. Science in December, he found that a small subset of people – and a greater proportion of children compared to adults – carried antibodies from previous coronavirus infections that were able to neutralize or disarm SARS-CoV-2.
“It’s not surprising” that the new study found that these antibodies cannot prevent infection, said George Kassiotis, an immunologist at the Francis Crick Institute in the United Kingdom, who led the other study published in Science in December. Antibodies that act against multiple coronaviruses exist in only a few individuals and at very low levels, said Kassiotis. Children get sick with common colds much more than adults, which “means that their antibodies against the common cold coronavirus don’t even stop them [from] catching more common colds – it would be quite strange if they could stop them from catching the pandemic virus,” he said.
That is not the issue, he said. Instead, the researchers want to know if these antibodies can modify the disease once you have contracted the virus, such as to protect you from severe symptoms, Kassiotis told Live Science. “The new study suggests[s] they don’t want to, but I don’t think that’s conclusive. “
Antibody file
In the new study, Hensley and his team analyzed serum samples collected in 2017 to determine the level of antibodies against seasonal antibodies carried by the general population. Blood samples were collected from 263 children at the Children’s Hospital of Philadelphia and from 168 adults at the Penn Medicine Biobank.
Most of these samples contained antibodies to seasonal coronaviruses, but only about 20% of them contained antibodies that also had the ability to bind to the SARS-CoV-2 spike protein (the weapon the virus uses to invade human cells) or its nucleocapsid protein (a protein essential for virus replication).
They then analyzed 502 other serum samples taken from people before the pandemic; half of these people tested positive for SARS-CoV-2 after the pandemic struck and half did not and were used as a control group. Likewise, they found that more than 20% of these samples contained antibodies against the coronavirus that could bind to SARS-CoV-2. However, people who had these antibodies still developed SARS-CoV-2. There was no correlation between the level of these antibodies and the severity of the COVID-19 they developed, the study concluded.
In the third part of the experiment, they analyzed serum samples from 27 patients hospitalized with COVID-19 and found that the infection increased the body’s antibody levels against seasonal coronaviruses. Another study published in December 2020 in the journal Clinical Infectious Diseases Likewise, they found that these antibodies do not provide any neutralizing effects. But Kassiotis’s study found that some of the antibodies that could bind to SARS-CoV-2 could neutralize the virus.
It is not clear whether these discrepancies are due to differences in the way they tested their samples or other factors, such as geographical differences, the authors wrote. Kassiotis thinks it is because the researchers used a less sensitive test and therefore did not identify enough people (two in the year before the pandemic and 11 in total) with antibodies that could bind to the peak protein. “These numbers are too small for any significant conclusions.”
In any case, even if more studies, larger ones confirm that seasonal coronavirus antibodies are not protective, which does not mean that there are no other types of immune cells, in addition to antibodies that are remnants of past cold infections that could play a protective role and have not yet been tested, according to the statement. For example, T cells that respond to the original SARS-COV-1 virus remain for decades and some also bind to SARS-CoV-2, a July 2020 study published in the journal Nature found.
“Although antibodies from previous coronavirus infections cannot prevent SARS-CoV-2 infections, it is possible that pre-existing memory B and T cells may provide some level of protection or at least reduce the severity of COVID- 19 “, Hensley said. “Studies need to be completed to test this hypothesis.”
Originally published on Live Science.