Three people who previously recovered from Covid-19 were protected during a major outbreak of the disease onboard a fishing vessel that left from Seattle, US, according to a new study that offers the first confirmation that having antibodies are enough to prevent a second infection.
The findings were based on antibody (serological) as well as viral detection (reverse transcriptase-polymerase chain reaction, or RT-PCR) tests that were conducted before the vessel departed and upon its return. During its 18 days at sea, 104 of the 122 crew members contracted the virus from a single source.
“This suggests that neutralising antibodies are a correlate of protection for Sars-CoV-2, with obvious caveat that more study is needed since the N (number of people with antibodies) was small,” Alexander Greninger, the assistant director of the University of Washington (UW) Medicine Clinical Virology Laboratory and one of the authors of the study, said in an email response to HT.
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The study was posted on Friday on the preprint server medRxiv and the researchers were from UW as well as Seattle’s Fred Hutch Cancer Research Center,
The findings are significant since they are the closest confirmation yet that the world’s main strategy of using vaccines to trigger immune response could indeed work to stop the pandemic. This addresses a complicated question of whether antibodies are enough to prevent disease, and ensure symptoms are mild, or have no effect at all.
Deriving such data is normally challenging since scientific ethics prohibit an intentional infection of a person with antibodies to check whether they are safe from the virus.
“A total of 104 individuals had an RT-PCR positive viral test… yielding an attack rate on board of 85.2%. Only three crewmembers tested seropositive prior to departure in initial serological screening and also had neutralizing and spike-reactive antibodies in follow-up assays… None of these crewmembers showed evidence of bona fide viral infection or experienced any symptoms during the outbreak,” the researchers said in their paper.
The analysis involved detailed follow-up tests for 50 days. The researchers also carried out a genomic analysis of 39 genomes from the outbreak and determined that the outbreak was caused by a single source.
Since in all 18 people did not contract the virus, the authors acknowledge a faint chance that the three crew members with antibodies may not have had close contact. “There is always a possibility that they were not exposed but [that is] unlikely given the high attack rate,” said Greninger.
The study also highlights how some antibody tests may be more reliable than others. In the initial serological sampling, six people appeared to have antibodies.
This difference is a result of the human body mounting a varied counterattack against a virus, and detecting these is a complicated process. For instance, in this case, the pre-departure samples were tested using the Abbott Architect kit that looks for antibodies to a specific protein of the virus known as the Nucleocapsid (N).
Once the researchers found out there was