When you have a global pandemic like COVID brushing up against the labyrinthine business dynamics of the drug industry, things can get tricky. Simply inventing a new vaccine or therapeutic is a time-consuming and unpredictable process in and of itself. And then you have to actually make this new product at scale so that shots can be delivered to vaccine sites and administered into arms.

That makes on-the-ground contract manufacturers—companies that may not be household names but serve a critical role in the drugmaking process—particularly important in this moment. These are the companies that help manufacture drug doses or carry out other important functions that not all drugmakers have the capacity to do, such as putting a COVID vaccine into vials so they can actually get to patients.

The COVID outbreak has led to a spider’s web of relationships among these third-party contract firms and the pharma industry partners they work with, and experts tell Fortune that it’s tough to predict outright how the pandemic may reshape these outsourcing companies’ bottom lines and their business strategies—not to mention what their roles will be in the future as variant strains of the coronavirus emerge.

Some of the giants in the drug contract-manufacturing space may benefit from knowledge of a certain coronavirus vaccine technology to maximize doses; others may not have the capacity or know-how to create customized biological ingredients relying on new vaccine platforms such as Pfizer’s and Moderna’s messenger RNA (mRNA)-based tech, but still may be able to scale up other kinds of COVID shots from companies like Johnson & Johnson or AstraZeneca. And still others may have to take on bigger roles in manufacturing non-COVID pharmaceuticals as giants like Pfizer focus their own manufacturing facilities on vaccine production.

“The good news is that there is enough capacity worldwide,” says Simone Blayer, a chemical engineer and pharma industry veteran who is now the head of chemistry, manufacturing, and control at the nonprofit PATH, which works to help improve vaccine production and equity around the world. “So then we see that the hardware, the volume of manufacturing, that is available for worldwide production meets the demand.”

Middlemen abound in the life sciences business generally. During a public health emergency, ad hoc relationships must be and have been struck between rivals and industry players globally to ensure that as many vaccine doses as feasible wind up in as many arms as possible, industry executives relayed to Fortune. There are just three emergency-authorized COVID vaccines in the U.S., with Johnson & Johnson's on a temporary pause over potential safety concerns. More than 192 million doses have already been administered across the country as of April 13, according to the CDC.

What happens for individual contract-manufacturing firms going forward is a far more nuanced story.

What are these companies and what do they do, anyway?

It might be easy to think that drugmakers, the so-called innovator companies behind a pharmaceutical product, are the only real parties involved in rolling out a new therapy. These include companies like Pfizer and its partner BioNTech, and Moderna, which both leveraged pioneering mRNA technology to win the first authorizations for COVID vaccines in the U.S. Johnson & Johnson and AstraZeneca both utilize something called an adenovirus, or cold virus, to create their vaccines, although J&J uses a human adenovirus while AstraZeneca uses one from a chimpanzee. Dozens upon dozens of other coronavirus vaccines are in various stages of clinical trials or authorization around the world, encompassing pharmaceutical giants and life science industry upstarts alike.

But once a product is proven, many pharma companies rely on outsourced manufacturing. The ever-changing innovation in the field requires these manufacturers to have sharp in-house scientific expertise and the willingness to take risks on unproven products during an emergency. And producing that initial substance, the “bulk” biological substance that makes up the core of something like a vaccine, is no mean feat.

But despite the less than ideal business conditions, this type of manufacturing is only gaining steam. Biopharmaceutical firms’ reliance on outsourced manufacturing for drugs of all stripes is a growing market, according to analysts. A report from Grand View Research finds that the global contract-manufacturing and development market for drugs will balloon to $157.7 billion by 2025, representing a 6.9% compound annual growth rate over seven years. That would make for a faster rate of growth among these third-party players than in the pharma industry itself.

How COVID has shaken up the industry landscape

“The coronavirus pandemic has resulted in disruptions in the supply chain of the overall pharmaceutical industry,” writes Grand View Research analysts in a more recent report on COVID’s effects on industry. “However, the biopharmaceutical [contract manufacturers and researchers] have responded well to the outbreak as such organizations are the beneficiaries of supply-chain disruptions.”

Depending on the exact COVID vaccine, pharma companies are exploring different strategies for working with manufacturers based on their vaccines' individual technologies.

For instance, Pfizer’s vaccine has such specialized requirements, particularly with its cold-chain requirements that necessitate super-cooled storage and distribution, that the drugmaker has largely relied on its own existing manufacturing facilities to scale up the product. The company has stated that it has some 40 sites that it owns to ramp up vaccine production and more than 200 suppliers who assist in the distribution process. Pfizer has outsourced production of its non-COVID drugs to outside manufacturers to clear up space for vaccine production at its own plants.

For mRNA-based vaccines, which rely on breaking down the genetic code of a virus and potential future variants of a pathogen, you need some institutional know-how. That’s why the likes of Catalent and Switzerland-based manufacturer Lonza have a distinct advantage over smaller contract manufacturers that don’t have the requisite institutional knowledge or infrastructure to make mRNA vaccines.

Catalent, for instance, is supporting the scale-up of more than 80 COVID-related therapeutics and vaccines, including the manufacturing of Moderna’s, AstraZeneca’s, and Johnson & Johnson’s vaccines. The company already produces more than 70 billion doses of 7,000-plus pharmaceutical products around the globe annually and works with over 1,000 customers. This year, it expects to produce over 1 billion doses of COVID vaccines and therapeutics across more than 80 individual pandemic-related programs, according to the company.

The company, which has $3 billion a year in revenues, also plays a big role in the nuts and bolts of safely putting vaccine doses into a vial (in industry jargon, “fill and finish”).

Lonza, which is working with Moderna to scale up its vaccine, referred Fortune to the smaller biotech company.

“For us, with mRNA in particular, I would say, the contractors are an especially critical path upfront as suppliers, to help with our processes,” says Ray Jordan, chief corporate officer at Moderna and coincidentally a veteran of both Pfizer and Johnson & Johnson. “And then downstream to things like fill and finish, which is where once you have your drug substance and you're then trying to get it into the usable vials and so on, that process is not one that we have. So, we're entirely dependent on contract firms for that.”

That requires cross-industry collaboration during a global outbreak. “We're experienced running different types of complex biologic products into that fill process and scaling those products up,” says Mike Riley, president of Catalent’s North America biologics department. “Every product is a little bit different. It has its own sensitivities. And so when we have a new product, like, say, Moderna’s mRNA vaccine, it has specific handling requirements, has a very specific process that has a lot of complexity to it. But we have enough capability working in partnership with Moderna that we can figure out how to scale that product up to much larger scale.”

Other manufacturers have different expertise. Emergent BioSolutions, which had a recent snafu at a COVID manufacturing site in Baltimore that led to millions of wasted COVID vaccine doses, is assisting both Johnson & Johnson and AstraZeneca in those production efforts, which require a somewhat more old-school skill set than the mRNA vaccines.

This may require a drugmaker to share some of its technological methods with contract manufacturers in order to ensure the safe production of these vaccines. But it’s also what’s necessary to immunize the world.

How will these companies handle new COVID strains?

What does all of this mean for the future? After all, a virus evolves, as we’ve already seen with COVID-19. Businesses have to evolve to meet the moment as well. Whether or not they’ll be able to is a more open question, especially if the coronavirus begins to resemble the flu, necessitating new booster shots every year as the virus evolves.

PATH’s Blayer emphasizes that it’s too early to speculate, given the nature of the pandemic and constantly shifting technologies. But he, and multiple other experts who spoke with Fortune, said the success of contracting firms going forward when it comes to COVID will depend on their experience and existing capabilities—and willingness to learn new tricks.

“There aren't really a lot of players who are technologically capable of manufacturing these kinds of new vaccines of mRNA,” says Blayer, adding that less complex COVID vaccines could be “transferred to a contract manufacturer relatively easily.”

“Having a contract manufacturer that is capable of handling primary manufacturing but also secondary manufacturing of mRNA is much more complex,” he says.

It’s a point of institutional memory that Catalent’s Riley drives home. “We got involved in mRNA therapeutics several years ago, through a partnership with Moderna, in their personalized cancer vaccine program,” he says. “And we certainly saw the potential in the technology, and saw the benefit in developing capabilities and knowledge and capacity to be able to support these types of programs.”

Such is the nature of evolving science and drug development—a dynamic that has played out even more rapidly during the pandemic. Players from big pharma to small biotech will have to share knowledge with each other and their contract-manufacturing partners, and that could lead to a shift wherein smaller CMOs focus on more conventional drugs while larger ones shift more resources to helping in, and learning from, the fight against this virus.