Sanofi and GlaxoSmithKline, two of the world’s largest vaccine makers, will work together to speed development of a vaccine for the new coronavirus, combining existing efforts in a rare example of large pharmaceutical company collaboration.

Together, the drugmakers expect to begin initial clinical tests of their vaccine prototype in the second half of this year, faster than what Sanofi originally forecast when it first announced plans for one in February. Ambitiously, the two pharmas said they could “complete the development required for availability” by the back half of 2021.

Such quick advancement would just fit within the 12- to 18-month timeline for vaccine development frequently given by U.S. government officials, although it’s not exactly clear what kind of supportive data Sanofi and GSK expect to have in hand by next year.

Roger Connor, GSK’s president of vaccines, said the companies would be working out clinical timelines “hand in hand” with regulators.

“In this really accelerated timeline, we’ve still got a lot of work to do” to define the path forward, Connor told reporters on a Tuesday call.

Typically, vaccines are the product of years of development, emerging for widespread use only after clinical tests in thousands of patients prove their ability to protect against infection and, most importantly, their safety in healthy individuals. The urgency of the coronavirus pandemic, which has sickened nearly 2 million people globally through April 13, has pushed drugmakers to move faster than they have previously.

Whether the development process can be short-circuited and still produce a safe and effective vaccine is still an uncertain bet, though, and drugmakers large and small have opted to partner and collaborate on coronavirus research rather than trying alone.

The collaboration between Sanofi and GSK is the most notable example yet, bringing together two drugmakers collectively worth more than $200 billion.

“Strategic alliances among vaccine industry leaders are essential to make a coronavirus vaccine available as soon as possible,” said Rick Bright, director of the Biomedical Advanced Research and Development Authority, or BARDA, in a Tuesday statement announcing the collaboration.

BARDA, an arm of the U.S. Department of Health and Human Services, in mid-February agreed to partner with Sanofi on development of a vaccine against SARS-CoV-2, as the new coronavirus is known.

After Johnson & Johnson, the French drugmaker was the second large pharmaceutical company to announce plans for a SARS-CoV-2 vaccine, bringing experience and large-scale manufacturing to the table when most declared programs were by smaller, less tested biotech companies. Yet two of those​ biotechs — Cambridge, Massachusetts-based Moderna and Plymouth Meeting, Pennsylvania-headquartered Inovio Pharmaceuticals — have already advanced their vaccine candidates into human testing, capitalizing on the advantages offered by newer vaccine technologies.

Sanofi, by contrast, is using a more established recombinant DNA platform that’s been proven in the company’s quadrivalent influenza vaccine FluBlok, acquired via a 2017 buyout of Protein Sciences. (It is, however, also working with Translate Bio on another vaccine that’s akin to the one being developed by Moderna.)

For SARS-CoV-2, the pharma is designing its vaccine around a “spike” protein that is found on the surface of the virus and is essential to its ability to infect human cells. By priming the body against this protein —​ a common target among drugmakers in the coronavirus vaccine race —​ Sanofi and others hope to spur an immune response to the actual viral invaders.

GSK, which opted against developing its own vaccine, will add its “adjuvant” technology, used to make vaccines more potent and efficient. The British company has made its adjuvants available to other companies working on coronavirus vaccines through the Coalition for Epidemic Preparedness Innovations.

With Sanofi, however, GSK will work more closely. The two companies set up a “Joint Collaboration Task Force,” led by David Loew, Sanofi’s vaccine development head, and Roger Connor, president of GSK vaccines. Work on the vaccine will begin immediately under an agreement in principle, GSK and Sanofi said. Definitive deal terms will be finalized in the coming weeks.

Critically, both companies have the capacity to manufacture vaccines at a global scale.

“We believe that if we’re successful we’ll be able to make hundreds of millions of doses by the end of next year,” said GSK CEO Emma Walmsley on the call with reporters.

Walmsley declined to say how much the companies were investing in the partnership, but noted that GSK does not expect to profit across its coronavirus-related work. The company currently has seven partnerships set up and any short-term profit generated by a project would be reinvested into either ongoing coronavirus research or long-term epidemic preparedness, she said.