Hints of protective immunity against the pandemic coronavirus have surfaced in the throat of a recent COVID-19 outbreak that flooded the crew of a fishing vessel.
The coronavirus, SARS-CoV-2, infected 104 of the 122 people on board, about 85 percent, during a short voyage. But trawling through data collected before and after the ship set sail, researchers noted that the 18 spares for infection happened just to contain the only three people on board who had potent, pre-existing immune responses against SARS-CoV-2. Specifically, the three sailors were the only ones found to have SARS-CoV-2 neutralizing antibodies, which are proteins that circulate in the blood and completely infect the infected virus.
The numbers are small and the finding is not definitive. In addition, the study appeared this month on a pre-print server, meaning it has not been published by a scientific journal or peer-reviewed. Still, experts say the study was well done and important for netting data indicating that potential, pre-existing immune responses from an infection in the past may indeed protect someone from catching the virus again.
“Although this is a small study, it provides a remarkable, human experiment in life, at a time when we have been short on hardline, formal, evidence that neutralizing antibodies really offer protection against re-infection, as provided by animal models,” Said Danny Altmann, a professor of immunology at Imperial College London, in a media statement.
Viral capture
For the study, researchers in Seattle, Washington were able to test 120 members of the 122-person crew before sailing. They searched for active infections by trying for SARS-CoV-2 genetic material in noses, and they searched for infections from the past by trying for antibodies that develop after the end of an infection. All 120 were negative for SARS-CoV-2 in their nose. However, six had antibodies against the pandemic virus.
Upon further investigation of those six with antibodies, only three had neutralizing antibodies, the researchers found. Although not all antibodies suggest past exposure to a virus, not all antibodies can neutralize viruses. And neutralizing antibodies are considered critical for protective immunity.
The researchers could not say for sure what happened to the three who had some antibodies but did not neutralize antibodies. Their best judgment is that they just had false positive test results and really no antibodies against SARS-CoV-2. But it is also possible that they had decreasing antibody responses, often from a remote infection at the onset of the infection, or a growing antibody response in the early stages of an infection. However, after the ship sailed and the COVID-19 outbreak struck, all three were infected with SARS-CoV-2.
Claims for immunity
When the ship returned after about 16 days at sea, with sick on board, the investigators examined all crew members and followed them for up to 32 days. A total of 104 were infected, including one of the two crew members they did not test at first.
As for the three with neutralizing antibodies, initial tests for SARS-CoV-2 genetic material in their noses were all negative. Two of the three tested negative at three different times – from the day they got off the boat to 18 days later. The third crew member tested negative after three and ten days of dismissal. But in a data breach, this person had very weak positive tests for seven days and 13 days after getting off the boat. The tests did not qualify as positive, based on pre-set criteria. But it suggests that some residual viral material lay in the person’s nose – something that has been seen in other studies.
Despite the limitations of the study and quarks of the data, experts say it is well done and useful information. Jonathan Ball, professor of molecular virology at the University of Nottingham, stated in a media statement that although the study was small and left early questions, it “gives us important insight into the type of immunity that can protect against future infection.”
