Participants in the first-stage clinical trial of a potential vaccine for Covid-19 by Moderna showed antibody levels started to decline 41 days later.

Following trial results released yesterday showing Moderna’s vaccine candidate might not be safe for human consumption – apparently, the candidate caused “adverse” reactions in roughly 50% of patients who participated in a recent study – the dozens of companies, universities and governments working on COVID-19 vaccine candidates just received another piece of disheartening news:

A growing body of evidence gleaned from research into the virus suggests that antibodies may not offer protection for more than 2-3 months, for many people.

Now, a study produced by researchers at King’s College London is showing recovered patients antibodies declined significantly within months of infection, raising the critical question of whether a vaccine could ever provide lasting protection. Moderna’s vaccine candidate has shown the capacity to produce antibodies in test subjects, but it’s still unclear exactly how much protection this might provide.

University of Nottingham Emeritus Professor in Immunology Herb Sewell, who consulted on the study, said it appeared to show that antibodies to the virus disappeared more quickly than antibodies for MERS and other coronaviruses.

Viruses like SARS elicited an immune response that lasted at least a couple of years.

This suggests that the eventual COVID-19 vaccine might need to be administered every year to offer a reliable level of protection.

“If the vaccine response drops off like the natural response does, it does mean we’d have to give repeat ones,” he said.

But that’s not set in stone – at least, not yet. As the FT points out, seeing some degree in decline of efficacy is typically expected. That doesn’t mean the body won’t be able to reproduce those same antibodies even more quickly the next time it is infected.

Researchers also apparently found evidence showing a link between the intensity of symptoms and the durability of antibodies. The lighter the symptoms, the lower the level of apparent immunity.

It is normal to see some decline in antibody loads after a vaccine, which will still be effective if the body can subsequently produce antibodies more quickly when exposed to the virus again. Importantly, the body does not always respond in the same way to a vaccine as it does to an infection. Tal Zaks, chief medical officer at Moderna, said he believed it was “entirely plausible” that the antibodies fade, but that it might be because those patients were asymptomatic or started with lower levels of antibodies.

“They seem to lose them more quickly, which probably speaks to the quality and type of immune response to begin with,” he said. “It’s reassuring to see that we achieve neutralising antibodies that are consistently above what you see from people who’ve actually been sick, so we expect they are going to be protected.”

Several high profile studies have raised doubts about whether these antibodies are permanent, or effective, or not. But only large-scale clinical trials will eventually lead humanity to the truth, even as local officials rely on antibody detection tests of questionable quality to try to estimate the number of people in an area who contracted the virus.

Notes:

Betty Diamond, director at the Feinstein Institutes for Medical Research in New York, said the Moderna results were “encouraging” but more information was needed about how long the response will last. Participants’ antibody levels started to decline 41 days after the vaccine, but the trial data only went until 57 days. 

“Vaccines present antigen differently than natural infection and use different adjuvants [chemical boosters], therefore there is no reason to assume the immune memory will be the same with vaccines as with natural infection,” she said.

It will be important that a vaccine induces a high level of antibodies from the start. Umer Raffat, an analyst at Evercore ISI, said on a call with investors that the participants’ response to Moderna’s potential vaccine had been “materially higher” than other candidates including those from US-based Inovio and Chinese company CanSino Biologics. 

While it was hard to compare them directly, the Moderna vaccine also seemed to induce a better response than the vaccine being developed by Pfizer with BioNTech, Mr Raffat said.

Both are using a novel technique called messengerRNA to transcribe the virus’s spike protein into a human cell to show it to the immune system.

“Confirmation of the correlation between antibody titers [concentration] and protection against Covid-19 will be possible only in a large clinical efficacy study,” he wrote in an opinion article that accompanied the publication of the peer-reviewed data on Moderna’s vaccine candidate.

And as scientists try to leave all their options open, some of the vaccines in development are examining the body’s T-cell response to the infection, something researchers suspect could help hold the key to developing a successful vaccine.

Mr Raffat said he had heard AstraZeneca would show a robust response from both T-cells and antibodies to the vaccine it is developing with the University of Oxford.

AstraZeneca did not respond to a request for comment.

On the call with investors on Wednesday, Mr Raffat said: “If I want to take a vaccine in January, I’ll probably want to take Astra for a T-cell response and Moderna or Pfizer BioNTech for a neutralising antibody response.”

Source: FINANCIAL TIMES