Childhood colds don’t prevent coronavirus infection, a study finds.

The theory was compelling: Could children be less vulnerable to the new coronavirus because they carry antibodies to other coronaviruses that cause the common cold? Might that also help explain why some people infected with the new virus have mild symptoms while others are more severely affected?

The notion gained traction particularly among people who thought it would swiftly bring about herd immunity. A study in the journal Science, published in December, gave the hypothesis a strong boost.

But a new study published on Tuesday in the journal Cell found that the theory does not hold up. Based on experiments with live virus and with 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, called SARS-CoV-2.

“Going into this study, 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 one in five people carries antibodies that recognize the new coronavirus.

But the team found that these antibodies are not neutralizing — they cannot disarm the virus, nor do they mitigate the severity of symptoms after infection.

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