The theory was simple and compelling: Children are less vulnerable to the new coronavirus because they carry antibodies to other common coronaviruses that cause the common cold.
But for all its appeal, the theory is simply not true, said a new study published in the journal Cell. Based on carefully conducted experiments with live virus and hundreds of blood samples drawn before and after the pandemic, the research refutes the idea that antibodies to seasonal coronaviruses have any impact on the new coronavirus, SARS-CoV-2.
"We thought we would learn that individuals that had pre-existing, pre-pandemic antibodies against SARS-CoV-2 would be less susceptible to infection and have less severe COVID-19 disease," said 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 age 5. As a result, about 1 in 5 people carries antibodies that recognize the new coronavirus. But these antibodies cannot disarm the virus.
The researchers also compared antibodies to common cold coronaviruses in children and adults and found no difference in the amounts. By contrast, a study in Science in December had reported that about 5% of adults carried those antibodies, compared with 43% of children.
Some experts said they found Hensley's study to be more consistent with circumstances in which large groups of people become infected with the new coronavirus.
"The idea that having the snuffles a while back somehow protects you from SARS-CoV-2 infection has always left me cold, but it's been a persistent urban legend throughout the pandemic," he said.
Experts praised the study's careful and rigorous approach.
"The theory that existing antibodies can protect people from the new virus has definitely got a strong appeal, because, at first blush, it can explain a lot of the pandemic," said Shane Crotty, a virologist at the La Jolla Institute of Immunology. "But a beautiful idea doesn't make it true."
The most important part of the coronavirus is the spike protein on its surface, which docks onto human cells. The spike is also the most distinctive part of the virus, so it makes sense that antibodies to seasonal viruses would be unlikely to recognize and disarm it, said Marion Pepper, an immunologist at the University of Washington in Seattle. She said, "There are very specific parts of these viruses that are critical for infection."