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A New Type Of COVID-19 Vaccine

A New Type Of COVID-19 Vaccine Could Debut Soon

 

A vial of the experimental Novavax coronavirus vaccine is ready for use in a London study in 2020. Novavax’s vaccine candidate contains a noninfectious bit of the virus — the spike protein — with a substance called an adjuvant added that helps the body generate a strong immune response.

Alastair Grant/AP

A new kind of COVID-19 vaccine could be available as soon as this summer.

It’s what’s known as a protein subunit vaccine. It works somewhat differently from the current crop of vaccines authorized for use in the U.S. but is based on a well-understood technology and doesn’t require special refrigeration.

In general, vaccines work by showing people’s immune systems something that looks like the virus but really isn’t. Consider it an advance warning; if the real virus ever turns up, the immune system is ready to try to squelch it.

In the case of the coronavirus, that “something” is one of the proteins in the virus — the spike protein.

The vaccines made by Johnson & Johnson, Moderna and Pfizer contain genetic instructions for the spike protein, and it’s up to the cells in our bodies to make the protein itself.

The first protein subunit COVID-19 vaccine to become available will likely come from the biotech company, Novavax. In contrast to the three vaccines already authorized in the U.S., it contains the spike protein itself — no need to make it, it’s already made — along with an adjuvant that enhances the immune system’s response, to make the vaccine even more protective.

Protein subunit vaccines made this way have been around for a while. There are vaccines on the market for hepatitis B and pertussis based on this technology.

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A large test of the Novavax COVID-19 vaccine’s effectiveness, conducted in tens of thousands of volunteers in the United States and Mexico, is about to wrap up. Dr. Gregory Glenn, president of research and development for Novavax, told an audience at a recent webinar hosted by the International Society for Vaccines that “we anticipate filing for authorization in the U.K., U.S. and Europe in the third quarter.”

Turning plants into factories

To make the virus protein, Novavax uses giant vats of cells grown in the lab. But there’s another way to make the protein: Get plants in a greenhouse to do it.

That’s the approach being used by the Canadian biotech firm Medicago.

The plants used are related to the tobacco plant, and have been modified to contain the genetic instructions to make the viral protein.

The plants do something very valuable — they make a lipid shell that surrounds a bunch of the viral proteins, with the proteins sticking out.

“The plant will assemble the protein in a shape and form that is looking like the virus,” says Nathalie Landry, Medicago’s executive vice president for scientific and medical affairs. “So, if you look at an image of it, it looks like a virus, but it cannot induce any disease. But when [it’s] injected as a vaccine your body will raise a good immune response.”

 

Early studies suggest Medicago’s candidate vaccine does just that, and the company is confident enough in those findings that it’s already begun a large study in people that could involve as many as 30,000 volunteers in 11 countries.

Landry acknowledges that development of the Medicago COVID-19 vaccine has lagged behind others.

“We’re a latecomer, but we’re coming,” she says.

Another latecomer that’s coming is the pharmaceutical giant Sanofi. Its protein subunit vaccine against the coronavirus is also grown in cells in the lab.

Late last year the company was getting ready to mount a large study of the vaccine’s effectiveness when the early results in a smaller group of people showed it did not seem to be inducing the immune response that would be protective.

“Especially in elderly individuals in that study, it was not as immunogenic as it should be,” says Dr. Paul Goepfert at the University of Alabama at Birmingham, who was one of the researchers involved in those early studies. He says the issue turned out to be an incorrect calculation of the dose of vaccine being delivered.

“So instead of giving 10 micrograms of the dose, they were actually giving one microgram,” Goepfert says.

Sanofi has fixed that problem and repeated the early studies with good results. The company is now enrolling volunteers in a large efficacy trial.

Goepfert says it’ll be a good thing if all these vaccines make it to consumers. But that alone isn’t going to solve the problem of getting people vaccinated.

Why? “Because the vaccines that we have now are just beyond our wildest dreams kind of effective,” he says. “And I’m living in a state right now where it just frustrates me how slow our vaccine uptake is.”

Goepfert lives in Alabama. According to the latest numbers from the Centers for Disease Control and Prevention, only Mississippi has a lower per capita rate of vaccination.

 

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What are protein subunit vaccines and how could they be used against COVID-19?

All vaccines work by exposing the body to molecules from the target pathogen to trigger an immune response – but the method of exposure varies. Here’s how subunit vaccines work.

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AT A GLANCE

Rather than injecting a whole pathogen to trigger an immune response, subunit vaccines (sometimes called acellular vaccines) contain purified pieces of it, which have been specially selected for their ability to stimulate immune cells. Because these fragments are incapable of causing disease, subunit vaccines are considered very safe. There are several types: protein subunit vaccines contain specific isolated proteins from viral or bacterial pathogens; polysaccharide vaccines contain chains of sugar molecules (polysaccharides) found in the cell walls of some bacteria; conjugate subunit vaccines bind a polysaccharide chain to a carrier protein to try and boost the immune response. Only protein subunit vaccines are being developed against the virus that causes COVID-19.

Other subunit vaccines are already in widespread use. Examples include the hepatitis B and acellular pertussis vaccines (protein subunit), the pneumococcal polysaccharide vaccine (polysaccharide), and the MenACWY vaccine, which contains polysaccharides from the surface of four types of the bacteria which causes meningococcal disease joined to diphtheria or tetanus toxoid (conjugate subunit).

ADVANTAGES AND DISADVANTAGES OF PROTEIN SUBUNIT VACCINES

Well-established technology

Suitable for people with compromised immune systems

No live components, so no risk of the vaccine triggering disease

Relatively stable

Relatively complex to manufacture

Adjuvants and booster shots may be required

Determining the best antigen combination takes time

HOW DO SUBUNIT VACCINES TRIGGER IMMUNITY?

Subunit vaccines contain fragments of protein and/or polysaccharide from the pathogen, which have been carefully studied to identify which combinations of these molecules are likely to produce a strong and effective immune response. By restricting the immune system’s access to the pathogen in this way, the risk of side effects is minimised. Such vaccines are also relatively cheap and easy to produce, and more stable than those containing whole viruses or bacteria.

A downside of this precision is that the antigens used to elicit an immune response may lack molecular structures called pathogen-associated molecular patterns which are common to a class of pathogen. These structures can be read by immune cells and recognised as danger signals, so their absence may result in a weaker immune response. Also, because the antigens do not infect cells, subunit vaccines mainly only trigger antibody-mediated immune responses. Again, this means the immune response may be weaker than with other types of vaccines. To overcome this problem, subunit vaccines are sometimes delivered alongside adjuvants (agents that stimulate the immune system) and booster doses may be required.

HOW EASY ARE THEY TO MANUFACTURE?

All subunit vaccines are made using living organisms, such as bacteria and yeast, which require substrates on which to grow them, and strict hygiene to avoid contamination with other organisms. This makes them more expensive to produce than chemically-synthesised vaccines, such as RNA vaccines. The precise manufacturing method depends on the type of subunit vaccine being produced. Protein subunit vaccines, such as the recombinant hepatitis B vaccine, are made by inserting the genetic code for the antigen into yeast cells, which are relatively easy to grow and capable of synthesising large amounts of protein. The yeast is grown in large fermentation tanks, and then split open, allowing the antigen to be harvested. This purified protein is then added to other vaccine components, such as preservatives to keep it stable, and adjuvants to boost the immune response – in this case alum. For polysaccharide or conjugate vaccines, the polysaccharide is produced by growing bacteria in industrial bioreactors, before splitting them open and harvesting the polysaccharide from their cell walls. In the case of conjugate vaccines, the protein that the polysaccharide is attached to must also be prepared by growing a different type of bacteria in separate bioreactors. Once its proteins are harvested, they are chemically attached to the polysaccharide, and then the remaining vaccine components added.

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