How To Accelerate Vaccine Production – And Avoid Speed Bumps

The COVID-19 pandemic put on display the various strategies available to make vaccines, some over a century old, others ramping up production for the first time. After the SARS-CoV-2 virus was sequenced in January 2020, the checkered flag waved, and each manufacturing route faced challenges in terms of scaling up. Some of these were unique to this pandemic situation, but racing from a lab – or pilot-scale start – to a finish line of full-scale production is always a bumpy ride. In this article, we discuss key challenges in vaccine development scale up, highlighting various strategies for overcoming them.

Nucleotides

RNA vaccines are the newest kids on the block. Their impact was largely unheralded prior to the pandemic, even though some predicted a new era in vaccinology. Certain pharmaceutical companies’ pipelines for mRNA vaccines targeted cancers, while others aimed for some infectious diseases. Manufacturing mRNA vaccines involves a polymerase enzyme creating a string of mRNA by linking nucleotides together, working from a DNA template.

“The challenge in scaling this up related to the fact that it was a very new technology and different from how [previous] vaccines had been manufactured,” says Dr. Zoltán Kis, an assistant professor in the department of chemical and biological engineering at the University of Sheffield. This is largely a cell free, enzymatic process, while other vaccines often involve growing large quantities of cells. All of the enzymes are made in bacteria, which taps into existing biotech knowhow. “Enzymes and the plasmid DNA are made using Escherichia coli (E. coli) fermentation, which has been used for decades in this way, so there was knowledge in the industry in how to scale-up recombinant protein production,” explains Kis.

Production was initially slowed by the step that encapsulated the mRNA into lipid spheres, where microfluidics was required to mix them in a controlled environment. This involved the use of proprietary bespoke lipids and exotic mixing technology, according to drug discovery chemist Derek Lowe. Now, mid-2022, all the steps in making mRNA vaccines have been ramped up in terms of production by multiple companies at sites in Europe and North America. “The RNA vaccines were scaled up in a straightforward way and saw them deployed at record speeds,’ says Kis.

This bodes well for the future scaling up of mRNA vaccines, especially since manufacturing processes themselves were under time pressure during the pandemic, and probably not optimized. “They had to achieve a near optimum, in the time allowed, so what was good enough basically,” says Kis. This likely leaves room for improving the process for future vaccines.

The Coalition for Epidemic Preparedness Innovation (CEPI) certainly sees room for advances here. “The cost driver is very much the raw materials, so that is something we will look at,” said Dr. Ingrid Kromann, acting director of vaccine manufacturing and supply chains at CEPI. “We support the mRNA platform because we see it has advantages in preparedness for the next disease X.” Template libraries against whole virus families could be built and made ready to adapt for rapid deployment, perhaps to contain a new disease outbreak from an unpredictable source (disease X).

CEPI is also looking to partner with manufacturers in low- and middle-income countries to make future vaccines using the mRNA platform.  In terms of scaling manufacture, some mRNA companies opted to do it internally, whereas others chose to outsource to a contract manufacturing organization. “This [mRNA vaccine] intellectual property is protected by trade secrets mostly. The processes are not often patented. The companies don’t disclose details of the manufacturing process,” says Kis. Normally, tech transfer like this would take two years. The timeframe was compressed for the pandemic emergency, he notes.

Professor Harris Makatsoris, process engineer at King’s College London, is leading a consortium seeking to use continuous manufacturing techniques to design and churn out mRNA vaccines, rapidly. This differs from the current batch process manufacturers use, “which is prone to risks of lost production and higher costs,” according to Makatsoris. The objective is to lower the cost of mRNA vaccines, developed against respiratory viruses such as those developed by Professor Robin Shattock’s group at Imperial College London, to less than $10 per dose, perhaps even $1, compared to the $20 price tag for today’s approved mRNA vaccines for COVID-19. “The process is at least conceptually simple, because it does not require growing organisms like other types of vaccines, but the challenge is that the inputs are very expensive,” notes Makatsoris. In particular, he believes the process of encapsuling RNA into the sphere-shaped lipids can be improved in numerous ways, so that more product can be obtained with the same quantities of materials, compared to current methods.

Next year, Makatsoris aims for his “biofoundry-in-a-box” project to build pilot plants near Newcastle and later near Reading in the UK. This is to validate and manufacture up to 50 g of RNA per day, which would supply millions of doses. Such a plant would cost a fraction, he says, of the $200 to $300 million for a typical batch plant. “We hope this will make the manufacture of mRNA vaccines easily accessible in low- and middle-income countries,” says Makatsoris.

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Weakened and inactivated

Another newbie in terms of mass vaccine production during the pandemic has been viral vectors. Production involves growing up masses of human cells and then infecting them with a weakened adenovirus that has been engineered to carry the genetic recipe for the spike protein. “Production usually happens in 2,000 L tanks,” according to Kis. “There are many cells, and they grow, eat food, and do lots of complex things, which introduces lots of variability into the process,” he adds. “You make one batch, and there is no guarantee that the next one will be exactly the same.”

Nonetheless, viral vector vaccines are one of the platforms adopted by CEPI. This was also a fairly new way to make vaccines, so the infrastructure and know-how to produce these vaccines for millions of people did not exist. But the process wasn’t entirely new either. “Some multinational companies had already worked on this platform for many years,” says Kromann. “So, there was some experience in the industry.” Nonetheless, some teething problems were reported that resulted in a reduction of available COVID-19 doses in 2021.

The supply of viral vectors remains a difficulty, Dr. Qasim Rafiq, associate professor in cell and gene therapy bioprocess engineering at University College London said. He predicts improvements in supply of such vectors within the next two or three years. With the rise of RNA vaccines though, Rafiq cast some doubt on whether viral vector vaccines will have as much impact as expected. Indeed, Kis predicts a move away from this platform for vaccines, with a focus instead on delivering genes for cell and gene therapies. Not everyone agrees. Different platforms might better suit certain diseases. “It is important we have diversified portfolio of platforms,” says Kromann. “I don’t think it is one-size fits all.” 

Another way to make vaccines is to grow mammalian cells, infect them with a virus (such as SARS-CoV-2) and then to inactivate the virus and extract from the medium. This is viewed as obsolete technology for new vaccines in the western world, though it is used currently to make rabies and a polio vaccine. A crucial step in the process is to disable the virus, without structurally altering to a degree that the antibodies elicited by the vaccine are different from those needed for the virus.

China surprised the world in mass producing inactivated virus vaccines during the pandemic, with Sinopharm and CoronaVac accounting for almost half the 7.3 billion doses delivered globally, according to Nature last October. This involved growing monkey kidney cells, in a bioreactor. The entire process from bioreactor to packaging of the vaccine reportedly takes 48 days. “I was somewhat surprised that they made so much of [the vaccine] so quickly,” says Kis. “It was seen as old technology. There was no clarity on how this would play out.”

Vaccines can also be based on live weakened pathogens, with examples including measles, mumps, influenza and yellow fever. One of the most famous and impactful live vaccines is Bacillus Calmette–Guérin (BCG), which celebrated its 100^th anniversary as a tuberculosis vaccine last year. It remains the only approved vaccine for this devastating disease. Kromann, who worked on BCG while at the Staten Serum Institute in Copenhagen, says such live vaccines with weakened vaccines continue to play a role in disease prevention. “In Europe, we stopped developing live attenuated vaccines, because they can be difficult to characterize [for regulatory requirements] and prove that they are safe,” she notes. But BCG has the advantage of being easy and cheap to mass produce, with production happening in several regions of the world.  

Protein subunits

A final vaccine platform that has been the workhorse of vaccine manufacture for decades now is protein subunits. This relies on using fragments of the pathogen, usually made as recombinant proteins in biotech workhorses such as yeast, insect or mammalian cell cultures. These are formulated with so-called adjuvants to boost the immune response to the pathogen fragment. Examples include acellular pertussis and hepatitis B vaccines. Surprisingly, protein subunit vaccines did not make a major contribution to the early supply of COVID-19 vaccines, with the first only recently being approved for use in the US.

Industry knows how to manufacture these vaccines at enormous scale. “The protein part of the subunit vaccine is often not a challenge,” says Kromann, “Because you will have a huge yield. You’re able to produce perhaps 6,000 L, so the proteins are produced very cheaply.” Perhaps 25 μg will be needed per dose. The global capacity for these vaccines was enormous, CEPI recognized, but there is a weak link in the adjuvant component. “Currently there are not many adjuvants on the market with a proven safety profile,” notes Kromann.

“Adjuvants have issues in terms of producing them at scale and often they are the expensive part of a subunit vaccine,” says Kromann. Vaccine manufacturers only can pluck alum (aluminium hydroxide, aluminium phosphate) from the shelf, but otherwise must talk to the few companies with approved proprietary adjuvants. This can lead to supply concerns – one adjuvant requires a saponin compound extracted from the bark of a Chilean tree, for example.   

There are, fortunately, many adjuvants in development and the pandemic saw the scaling up of production of several that are now used in vaccines recommended for emergency use authorization.

A geographical dimension

Plans to scale up vaccine production now must also take geography into account. “Our goal is for our future manufacturing network and preferred partners to have connections in regions,” says Kromann. Not only in Asia, but also in Africa, in South America and other areas such as southeast Asia.” She praises industry achievements in terms of vaccine production during the pandemic. “Look what they have done,” she concludes. “They have produced many billions of doses.”