An outbreak of COVID-19 on a fishing boat has provided scientists with the first direct evidence that antibodies really do protect people from re-infection.
More than 100 of the 122 crew members aboard the vessel were infected; but three sailors who had antibodies to the new coronavirus in their blood prior to the voyage — indicating a past infection — did not catch the virus a second time. These antibodies targeted the "spike protein" on SARS-CoV-2 that the virus uses to invade human cells.
Although scientists had suspected that having antibodies, particularly so-called "neutralizing antibodies," against COVID-19 would confer protection, they didn't have studies in humans to back that up.
"This is the first time to show that having these antibodies is a correlative of protection in people," study senior author Dr. Alex Greninger, an assistant professor of laboratory medicine and pathology at the University of Washington School of Medicine, said in a video released by the university.
The findings could be good news for candidate COVID-19 vaccines, which are generally trying to get the immune system to produce neutralizing antibodies against the virus, the authors said.
The study was posted Aug. 14 date to the pre-print database medRxiv, and has not yet been published in a peer reviewed journal.
The study researchers examined samples taken from crew members before and after the voyage. Prior to the boat's departure from Seattle in May, all 122 members were tested for SARS-CoV-2, the virus that causes COVID-19, and none tested positive. But three members were found to have neutralizing antibodies, which block the virus from infecting cells.
The boat's COVID-19 testing didn't stop infections from breaking out during the trip, and the vessel returned after 18 days at sea. A second round of testing revealed that more than 85% of crew members were infected with COVID-19.
Overall, 103 of the 117 crew members without neutralizing antibodies at the boat's departure were infected during the trip, compared with zero of the three members with neutralizing antibodies.
"This virus has shown the ability to infect a lot of people on boats ever since the beginning of the pandemic," Greninger said. "In a way, we're sort of turning the tide on the ships here, we're using them to learn things about our ability to protect ourselves."
The authors acknowledge that their study was small, with just three people having antibodies prior to departure. But the results were statistically significant, meaning there's a low likelihood that they are due to chance.
"Just looking at the numbers, it becomes clear that it’s unlikely that all of these three people were protected by chance," Florian Krammer, an immunologist at the Icahn School of Medicine at Mount Sinai in New York, told The New York Times.
The study also cannot determine how long antibodies would provide protection, and studies over longer periods will be needed to examine this, Greninger said.
The study also doesn't explain how a little over a dozen crew members apparently escaped infection without having preexisting immunity. It's possible that these crew members had jobs or behaviors that reduced exposure, Greninger told The Seattle Times.
Originally published on Live Science.