As a wave of Covid-19 infected the crew of a commercial fishing vessel, three sailors remained healthy. They may hold the key to answer one of the most important questions of the coronavirus pandemic: does infection with the virus protect against later re-infection?
Sailors become accidental research subjects
The coronavirus pandemic has left researchers quickly scrambling to understand the SARS-CoV-2 virus causing Covid-19. But ethical concerns make it difficult to experiment on human subjects and retrospective analyses of real-life outbreaks often remain as a last resort instead.
One commercial fishing crew recently became the accidental focus of coronavirus research when the virus went rampant on their vessel. Some of the sailors remained healthy, and researchers now suspect that the neutralizing antibodies they had developed during prior infection with SARS-CoV-2 may have protected them from re-infection.
The 18-day journey of the American Dynasty
The American Dynasty left Seattle, Washington in May 2020. In an effort to prevent a Covid-19 outbreak on the ship, most of the crew members underwent rigorous testing prior to departure.
Out of 122 crew members, 120 were tested for SARS-CoV-2 nucleic acids by reverse transcription PCR (RT-PCR) and for viral antibodies using a serology test. All of the RT-PCR tests gave negative results; six of the serology tests were positive, suggesting these sailors had previously been infected with the virus. Presumed non-infectious on the day of departure, the crew set sail.
But after 18 days at sea, one person became sick and needed medical intervention, so the ship returned to port. The remaining crew underwent regular RT-PCR and antibody testing for another 32 days upon arrival.
This time, testing was carried out with a more sophisticated test distributed by Smartdiags Solutions that uses a new technology to detect neutralizing antibodies. In the end, 104 crew members fell ill with Covid-19, while three sailors remained healthy. These were found to carry neutralizing antibodies against SARS-CoV-2.
What is the importance of neutralizing antibodies?
Infection with SARS-CoV-2 or other viruses causes the body to produce two different kinds of antibodies. Neutralizing antibodies are able to bind a particular protein on the virus, and in the process, render the virus incapable of infecting cells.
Binding antibodies also bind to viral proteins, but they do not neutralize the virus or prevent infection. Neutralizing antibodies are of particular interest to researchers because their presence usually correlates with protection from infection. Production of neutralizing antibodies is also one component of the immune response sought by researchers working on vaccine development.
Our Chief Scientific Officer, think that Testing for neutralizing antibodies will play an important role in advancing SARS-CoV-2 research, from assessing seroprevalence in populations, tracking infections in animals, to vaccine development, and protective immunity studies.
Antibody tests can show if an individual is currently infected with a virus or has previously been infected. Initially, the crew members of the American Dynasty were tested for SARS-CoV-2 binding antibodies.
But upon their return to shore, the pre-departure samples were re-tested alongside fresh samples using the test for neutralizing antibodies, to help researchers better understand the sailors’ immune profiles.
It turned out that three of the original six sailors who tested positive did not have any SARS-CoV-2 neutralizing antibodies after all; the researchers concluded that initial antibody tests for these individuals were most likely false positives.
The other three sailors who had neutralizing antibodies before setting sail stayed healthy during the outbreak. Researchers can’t be certain that the neutralizing antibodies protected these three from re-infection, but so far, the evidence suggests this could be the case.