The theory was simple and convincing: children are less vulnerable to the new coronavirus because they carry antibodies against other common coronaviruses that cause colds. The idea may also explain why some people infected with the new virus have mild symptoms, while others – presumably without antibodies against common cold coronaviruses – become much more serious.
The idea has attracted particular attention among people who claim that this existing protection will quickly bring human populations to herd immunity, the point at which the spread of a pathogen stops when the hosts run out to infect. A study in the journal Science, published in December, gave the hypothesis a strong boost.
But despite all its appeal, the theory does not hold up, according to a new study published Tuesday in the journal Cell. Based on carefully conducted experiments with live viruses and with hundreds of blood samples drawn before and after the pandemic, the new research refutes the idea that antibodies against seasonal coronavirus have any impact on the new coronavirus, called SARS-CoV-2.
“In this study, we thought we would learn that individuals with antibodies to SARS-CoV-2 that already existed would be less susceptible to infection and would have less severe Covid-19 disease,” says Scott. Hensley, an immunologist at the University of Pennsylvania. “That’s not what we found.”
He and his colleagues concluded that most people are exposed to seasonal coronaviruses by the age of 5 years. As a result, about one in five people carry antibodies that recognize the new coronavirus.
But these antibodies do not neutralize – they can not disarm the virus and also do not reduce the severity of symptoms after infection, the team found.
The researchers also compared antibodies with cold coronaviruses in children and adults and found no difference in the amounts. In contrast, the study in Science reported that about 5 percent of adults carry those antibodies, compared to 43 percent of children.
The study “reported very high levels of cross-reactive neutralizing antibodies before pandemic in children, something we did not find,” said Dr. Hensley said. (“Cross-reactive” refers to antibodies that can attack similar sites on more than one type of virus.)
“I honestly do not have an explanation for the difference in the science study,” he added.
Perhaps the difference in places – Pennsylvania, in its study against Britain in the previous investigation – could explain some of the difference, he said.
Other experts said they found that Dr. Hensley’s study is more convincing of the two and more in line with the circumstances in which large groups of people become infected with the new coronavirus.
For example, a single person infected with the new coronavirus in a Wisconsin summer camp caused an outbreak that affected 76 percent of the other participants, said John Moore, a virologist at Weill Cornell Medicine in New York. York, noted.
Similarly, on a fishing trawler that left Seattle for the sea, only three sailors who had antibodies against the new coronavirus remained virus-free. These are not the infection rates you would see if protective antibodies were widespread in the population, said Dr. Moore said.
“The idea that the sniffles were protected against SARS-CoV-2 infection a while back has always left me cold, but it has been a sustained urban legend throughout the pandemic,” he said. “Hopefully this new newspaper will eventually cool everyone down and put such thoughts in the freezer.”
Experts also praised the meticulous and meticulous approach of the new study.
“It’s really fun to do a study that’s done well,” said Shane Crotty, a virologist at the La Jolla Institute of Immunology in San Diego.
The theory that existing antibodies can protect people against the new virus certainly has a strong appeal, as it may initially explain much of the pandemic, ‘said Dr. Crotty said. “But a beautiful idea does not make it true.”
Dr. Hensley and his colleagues examined samples from 251 people who donated blood to the University of Pennsylvania before the pandemic and then developed Covid-19.
Those people had levels of antibodies that could recognize the new coronavirus, which was no different from those seen in blood samples from 251 people who did not remain infected. And the levels showed no association with the clinical outcome in any of the patients.
“It’s hard to get those kinds of samples – I was just impressed,” said Marion Pepper, an immunologist at the University of Washington in Seattle. “It’s like three different studies wrapped in one.”
The most important part of the coronavirus is the vein protein on its surface that falls on human cells. The peak is also the most characteristic part of the virus, so it makes sense that antibodies against seasonal viruses are unlikely to recognize and disarm it, said Dr. Pepper said.
“There are very specific parts of these viruses that are critical to infection, and most of this cross-reactivity is not targeted at those parts,” she said.
But George Kassiotis, an immunologist at the Francis Crick Institute in London, who led the study, which was published in Science, disagrees with the conclusions of the new research. This “confirms primarily rather than contradicts our key findings,” he said, adding that the new study was too small to rule out any role for existing antibodies.
But even if people wore coronavirus antibodies because of childhood infections, the protection they provide is not powerful enough to matter, said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle.
“If there is no effect that is measurable in a study with hundreds of people in both the infected and uninfected groups, then the effect is definitely small,” said Dr. Bloom said.
Most vaccines developed for the new coronavirus are focused on the vein protein. Some scientists have argued that antibodies against other parts of the virus can also be critical for protection. But the new study suggests that the other antibodies are of minimal importance in protecting humans from SARS-CoV-2.
The experts all said that the new study did not exclude a role for immune cells, memory B cells and T cells, which were produced in response to seasonal coronaviruses. Those cells can recognize and attack some parts of the new virus, which eases the severity of the symptoms.
However, the cells would not prevent infection, said Dr. Crotty said. When exposed to the new virus, the immune cells can “be fast enough that you will have an asymptomatic infection that you have never noticed,” he said. “But no, they will not stop infection.”
Tests of T cells are laborious and expensive, so the analysis of their contribution to immunity has not yet been completed. Meanwhile, the new study excludes at least an important role for existing antibodies, said dr. Hensley said: “We have written some chapter here, but there is still so much to learn.”