Covid-19 and antibodies: What scientists found after studying an outbreak on a fishing boat

  • 'Neutralising antibodies' are an important line of defence in the fight against Covid-19
  • A recent Seattle study sheds critical insight on how this offers protection against reinfection
  • However, the study has some limitations, including its sample size 

Immunity to Covid-19, the disease caused by the SARS-CoV-2 virus, is complicated. While antibodies are key to the body’s response to a viral infection, scientists have been battling to understand exactly what role they play in protection against Covid-19, and how long survivors will be protected against reinfection.

However, new evidence of an outbreak of the virus on a fishing boat with 122 people in the Seattle area suggests that antibodies may play a significant role in protecting people against reinfection.

During the trip, almost all the crew members got infected, but the ones with antibodies didn't.

The study was posted online in pre-print database medRxiv, but has not yet been published in a peer-reviewed journal.

The role of antibodies

Health24 previously explained that antibodies do their job by binding to specific parts of the virus, and neutralising the virus’s damaging effects.

These are called "neutralising antibodies", and if present, indicate two things: that the person has previously had SARS-CoV-2 infection, as they are only produced by infection; and that if that person encountered the virus again, the presence of antibodies would likely result in a level of protection.

Three crew members, neutralising antibodies

According to the study, all crew members were screened for the new coronavirus prior to their departure, with none of them testing positive.

However, three members were found to have neutralising antibodies in their blood (which blocks the virus from infecting cells in the body), indicating past infection of SARS-CoV-2.

After 18 days at sea, the ship returned to shore after a crew member fell ill, and all members were retested for the virus. Results showed that a total of 103 out of the 117 crew members without neutralising antibodies were infected during the trip.

In the case of the three sailors with neutralising antibodies, their tests came out negative. The researchers explain that their antibodies targeted the "spike protein" on the virus, which is used to invade human cells.

"This is the first time to show that having these antibodies is a correlative of protection in people," said study senior author Dr Alex Greninger, an assistant professor of laboratory medicine and pathology at the University of Washington School of Medicine, in a video released by the university.

Greninger added: "This virus has shown the ability to infect a lot of people on boats ever since the beginning of the pandemic.

"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."

Positive finding in light of vaccine development

The findings could help in vaccine development for Covid-19, as the candidate vaccines are aiming to get participants’ immune system to produce neutralising antibodies against the virus.

The results from the Oxford vaccine trial, published in The Lancet last month, showed that 90% of people developed neutralising antibodies after one dose of the vaccine, and of the ten people that were given two doses, all of them produced neutralising antibodies.

The authors of the latest study also note that although scientists suspect that having neutralising antibodies would protect against Covid-19, there are currently no studies in humans to back that up, with theirs being the first.

They have also acknowledged that their investigation is small, and that future studies should examine this over longer periods, as well as how long antibodies can provide protection.

Results are 'statistically significant'

A study from China recently found that some patients who recover from Covid-19 retain their antibodies against the disease for a short two to three months. Antibodies against other types of coronaviruses normally last around a year, Health24 reported.

On the other hand, the researchers of the fishing boat study wrote that their results are “statistically significant”, and Florian Krammer, an immunologist at the Icahn School of Medicine in New York, told The New York Times:

"Just looking at the numbers, it becomes clear that it’s unlikely that all of these three people were protected by chance," Krammer said.

Another unanswered question is how just over a dozen sailors, who were not found to have preexisting immunity, apparently escaped infection, but Greninger told The Seattle Times that there is a possibility that these members had jobs or behaviours that reduced exposure to the virus.

READ | Covid-19: Understanding immunity and what it means for a vaccine

READ | Can survivors get reinfected with coronavirus?

READ | Testing for Covid-19? All you need to know about antibody tests

Image: Aleksey Malinovski on Unsplash

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