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By La Provence (with AFP)
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Three crew members of a Seattle fishing boat who had antibodies capable of neutralizing the novel coronavirus were not reinfected during a Covid-19 outbreak that struck the majority of people on board, according to one study. “The presence of neutralizing antibodies from a previous infection was significantly associated with protection against reinfection”, conclude researchers from the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle.
This small study, which appeared on the Medrxiv prepublication site and not in a peer-reviewed journal, is one of the first in humans to suggest a link between neutralizing antibodies – those that prevent the virus from docking to cells – and protection against infection. 120 out of 122 people were tested before boarding the fishing boat in May, for both the presence of the active virus (virological test) and antibodies in the blood (serological test) indicating a previous infection.
None of the crew members tested positive for the virus by then, but six had contracted it before and therefore had antibodies in their blood.
Upon returning from the boat, a large majority of the crew members (85.2%) had been infected with the virus, including three among those who had antibodies in their blood before departure. But those who remained unharmed had proven neutralizing antibodies.
As for the other three, the fact that they were re-infected could be explained by the fact that their first infection, mild or asymptomatic, resulted in ephemeral production of antibodies or at a level too low to protect them. The researchers also do not rule out the possibility that the first serological result is a “false positive”.
For Jonathan Ball, professor of molecular virology at the University of Nottingham, who was not involved in the study, “This suggests that people who have been previously exposed to the virus are likely to re-infect themselves unless they have appreciable levels of neutralizing antibodies”. “This gives us important insight into the type of immunity that could protect against future infection”, but that doesn’t show, he says, whether or not past exposure may or may not protect against serious illness in people lacking detectable neutralizing antibodies. “It’s a very important discovery”, underlines Professor John Edmunds of the London School of Hygiene and Tropical Medicine. “This suggests that neutralizing antibodies may protect against infection”, which had not been demonstrated before in humans.
But for his colleague Professor Martin Hibberd, specialist in emerging infectious diseases “the small number of people studied makes this study difficult to fully interpret” and more conclusive studies should be available soon, “possibly from the large-scale phase 3 vaccine trials that are underway”.
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