Well that does three things:........

It prompts a great theory as to why Italy was hit so hard at the beginning.

It makes Trump's shutting of the borders with China look really pointless, especially as there was no attempt to deal with the virus already inside the USA and minimal testing.

It makes China even more culpable for the worldwide spread, because it reveals the depth of its coverup.

Pre-existing coronavirus antibodies could help protect children against new pandemic strain

https://medicalxpress.com/news/2020-11-pre-existing-coronavirus-antibodies-children-pandemic.html

In their paper, published in Science today (Friday 6 November), the scientists found that some people, notably children, have antibodies reactive to SARS-CoV-2 in their blood, despite not ever having being infected with the virus. These antibodies are likely the result of exposure to other coronaviruses, which cause a common cold and which have structural similarities with SARS-CoV-2.

The researchers made this discovery while developing highly sensitive antibody tests for COVID-19. To see how well their assay tests were performing, they compared the blood of patients with COVID-19 to patients who had not had the disease. Surprisingly, they found that some people who had not been exposed to SARS-CoV-2 had antibodies in their blood which would recognize the virus. To confirm their findings, they analyzed over 300 blood samples collected before the pandemic, between 2011 and 2018.

Nearly all samples had antibodies that reacted with common cold coronaviruses, which was expected given how everyone has been exposed to these viruses at some point in their lives. However, a small fraction of adult donors, about 1 in 20, also had antibodies that cross-reacted with SARS-CoV-2, and this was not dependent on recent infection with a common cold coronavirus.

Notably, such cross-reactive antibodies were found much more frequently in blood samples taken from children aged 6 to 16.