Massive Outbreak on Fishing Boat Suggests Antibodies Protect Against Coronavirus

The fishing boat 'American Dynasty', of the American company American Seafoods.

In the absence of experiments with humans in the laboratory - inadvisable with a potentially lethal virus that has no treatment - scientists are scanning the planet for natural experiments, whimsical events that can help better understand the plague of the new coronavirus. One of these unlikely phenomena began on May 13, when the American Dynasty boat , specialized in fishing for yellowfin sole, set sail from Seattle (USA) with 122 supposedly healthy crew on board. Little more than two weeks later, the ship had to return to port, after one of the workers became seriously ill and required hospitalization. 85% of the crew were infected with the coronavirus.

It is a fascinating natural experiment. Virtually all of the crew - 120 out of 122 - had been tested a day or two before sailing, with no sign of the virus. Three of them had neutralizing antibodies, the proteins produced by the human body to defend itself against the new coronavirus, an indication of having overcome the infection in the past. All 122 members were tested again upon arrival at port. "None of the three people who had neutralizing antibodies before sailing became infected during the outbreak," now stresses a group of researchers from the University of Washington, who has published a preliminary study on the case of the American Dynasty . "On the contrary, of the other 117 seronegative people [without detectable antibodies], 103 were infected," they emphasize.

The sample is very small, but the authors believe that this difference is statistically significant. "This is the first real-world data showing that antibodies protect against covid," say these virologists from the University of Washington, led by Alex Greninger. His study is currently a draft pending revision for publication in a specialized journal, but has already received applause from independent experts. Virologist Florian Krammer, from Mount Sinai Hospital in New York, has stated that this is "the first proof of the protective effect of previous infections."

"This is the first real-world data showing that antibodies protect against COVID," say virologists from the University of Washington

“They do not show that it is the antibodies - which are the way to measure that there has been a global immune response - but that the immune system globally protects. And deep down we already knew it ”, says the Spanish virologist Margarita del Val. “In the 22 million confirmed cases in the world, there will be some re-exposed to the infection. However, more serious reinfections or even as serious as the first ones are not described. They are benign or inapparent. Immunity is good, it protects. How long? We don't know ”, reflects Del Val, from the Severo Ochoa Molecular Biology Center in Madrid.

Neutralizing antibodies are capable of binding and blocking the virus. The new coronavirus uses its spicules, those protrusions that give it the shape of a medieval mace, as keys to open human cells. The antibodies render them useless, like gum sticking to a key. In the laboratory, different experiments on animals, from hamsters to mice, had already shown that neutralizing antibodies offer protection against SARS-CoV-2, but human evidence was lacking.

Alex Greninger's team recalls that some experimental covid vaccines, such as the one from the University of Oxford and that of the American company Moderna, produce levels of neutralizing antibodies similar to those observed in people infected with the coronavirus. However, antibodies have not yet been shown to protect in real life, even if taken for granted. The American Dynasty case is a good sign.

"The question now is how long these neutralizing antibodies last in the infected person," says virologist Isabel Sola

"It is the first time that an association has been observed in humans between the presence of neutralizing antibodies in the blood, as a result of a previous infection, and protection against a new infection", confirms virologist Isabel Sola, responsible together with her colleague Luis Enjuanes on the development of an experimental vaccine against coronavirus at the National Center for Biotechnology, in Madrid. Sola highlights one of the limitations of the new study: “Cellular immunity [another line of defense of the human body, starring a type of white blood cells, T lymphocytes], which is surely also contributing to protection, has not been taken into account ”.

“Overall, the observation is promising, because it suggests that the neutralizing antibodies that the vaccines induce may be contributing to protection. The question now is how long these neutralizing antibodies last in the infected person ”, says the virologist.

The fishing boat, a floating factory for frozen fish, also offers another lesson. In just two weeks, the virus was able to infect more than a hundred colleagues. The conditions were ideal: multiple, close and prolonged contacts in closed spaces. The coronavirus infected 85% of the workforce, despite the fact that preventive measures were taken, as stated in a statement Mikel Durham, the executive director of American Seafoods, the company that owns the fishing boat: “Despite our efforts, [.. .] the virus found us ”.

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