MILAN — A study by Milan’s Polyclinic hospital indicates the coronavirus was circulating among a random sample of blood donors with no symptoms in Milan before the first domestically transmitted case was confirmed Feb. 21 in a town less than an hour away.
The study of blood samples by donors showed that 4.6% already had antibodies against the virus at the start of the epidemic. Researchers concluded only 1 in 20 asymptomatic carriers had developed immunity, ‘’clearly showing that herd immunity remains a long way off.’’
That percentage rose to 7% by the beginning of April, when Italy was under lockdown. As the lockdown wore on, longer-term immunity was more prevalent among younger donors, which researchers said indicates ‘’the social distancing practices seemed to have favored young people, who had time to develop long-term immunity.’’
The study, involving researchers at the Polyclinic, Milan University, Sacco Hospital and the European Oncological Institute, was released in a preliminary form before being submitted to scientific journals for peer review.
They analyzed random blood samples from Feb. 8 to April 24 of 800 donors at the Polyclinic, which runs a transfusion center with more than 40,000 annual donors. The researchers say all donors who tested positive showed changes in the cell count and lipid profiles, which could provide clues to identifying asymptomatic carriers.
Okay this is a confusing piece. I think that the idea is that this was a longitudinal study, comparing the number of donors with antibodies over time. They seem to assume that donors were asymptomatic carriers because they must screen people who knew they were exposed? That part I think I get.
But how can they draw a conclusion about young people being better at developing antibodies if as a group they are more likely to be asymptomatic blood donors?
I also don’t understand how 5% of donors had antibodies as early as February — this implies it was widely circulating asymptomatically before it started causing symptoms. Is the implication it had to go through a number of passages before becoming dangerous? I had not heard that before.
It’s possible the antibody test was not refined enough to detect specifically C-19 and exclude all other coronvirus infections. I’m remembering that a really good C-19 test did not come out until the start of April??
What’s more interesting here is that the blood transfusions from these donors did not cause C-19 in the recipients. A big red flag would have been waving, if it had. It’s worth following up whether this population had a true C-19 antibody load or if this was a coronavirus varient that successfully passed the blood transfusion screenings.
I too found aspects of this AP article to be nonsensical, the above sentence being a prime example.
The actual manuscript can be found at : https://www.medrxiv.org/content/10.1101/2020.05.11.20098442v1.full.pdf+html
The article makes no comment at all regarding herd immunity and the data does not provide anything the would allow for a conclusion about how many “asymptomatic carriers” develop immunity. It does suggest that at the start of the Milan contagion 1 in 20 asymptomatic blood donors had been infected and were already developing immunity, not 1 in 20 “carriers”.
AP boilerplate.