The eyes of the scientific world have been on a Covid-stricken fishing vessel that seems to have provided the first real evidence outside of a lab that antibodies do indeed protect against reinfection. By Helen Compson.

Before the factory trawler FV American Dynasty set off from Seattle in May, blood samples collected from its 122 crew members showed that three of them had at some point had Coronavirus and displayed robust levels of neutralizing antibodies.

During the following few weeks, as the trawler fished off the Washington coast, 104 (85%) of the people on board went down with the virus – but not the three concerned.

Interesting! said Prof. Peter Openshaw, professor of experimental medicine at Imperial College London and honorary physician in the Department of Respiratory Medicine at Imperial College NHS Trust.

A specialist in viral lung disease and the immune-pathogenesis of viral disease, he is the daily chairman of the New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG), which advises the Chief Medical Officer and the Scientific Advisory Group in Emergencies (SAGE).

“The key questions we are all waiting answers to at the moment are what type of immunity and what level of immunity protects against infection and, importantly, for how long?” he said. “Getting those answers is the number one priority.

“Linked to that is ‘what type of immunity will vaccines generate’ and will it be a more or less durable immunity than that provided by natural infection?

“So, yes, it is interesting none of the three became infected in this high-incidence infection environment.”

Information was scant as yet, the scientific community at large knew only what been published in an article by Seattle epidemiologist Alexander L. Greninger.

Little was known generally about the conditions on board ship, what the sleeping arrangements and work patterns were, nor what type of symptoms the presumably young and relatively fit crew members had experienced.

However, said Prof. Openshaw, “this article has been interpreted as being hopeful in terms of indicating a level of antibody-assisted protection.

“But when the same three individuals were followed up a month later, there had been a significant decline in their antibody levels – two of them had come down to a level that might not be protective.

“So while it is interesting, I don’t think we should bring out the trumpets yet. It’s too early to estimate how long protection will last.

“There are big, big questions that still need answering and in terms of getting back to normal, I think we are all agreed the only way that’s going to happen is by the development of vaccines that can be rolled out on an enormous scale.

“But it is unlikely, even if that does happen, this virus is going to be eliminated in perpetuity.”

It was difficult, for starters, to eliminate viruses that were highly transmissible by people who were otherwise asymptomatic. They simply weren’t aware they were spreading it.

While it was comparatively easy to eradicate something as visible as smallpox – “not least because you can see somebody is infected and you can back off”, he said – with coronavirus, the infected often didn’t even feel unwell.

“Added to that, the fact the PCR test (the polymerase chain reaction test carried out via nose or throat swab) for virus detection is not 100% accurate means we are failing to diagnose it in some people who definitely do have Covid,” he said.

“PCR might only be about 70% accurate, so the mainstay of diagnosis is not wholly reliable, and the antibody tests that have been developed are still being refined, and then we don’t know which one of these tests is the most reliable in confirming if somebody has been infected.”

Around 15% of common cold strains are caused by common coronaviruses and studies have shown they offer a degree of immunity for up to 80 days, after which people can be re-infected with the same strain.

If that was true of SARS-CoV-2, the virus behind Covid-19, then it would be reasonable to estimate the antibodies would give two to three months’ protection.

“But that’s not necessarily the case,” said Prof. Openshaw. “Those coronaviruses have adapted to control the host immune system in a way that enables reinfection, while this is a novel coronavirus that has jumped species and might not have that adaptability.

“So, it could be a virus that the host could develop immunity to, for a minimum of two to three months, but perhaps for much longer.

“It could be possible to develop life-long immunity, but this virus hasn’t been in the human population long enough for us to know.

“We are in uncharted territory.”