Johnson & Johnson’s race to manufacture a billion doses of coronavirus vaccine is ramping up in a small biotechnology plant near Interstate 95 in Baltimore. But even as technicians prepare to lower 1,000-liter plastic bags of ingredients into steel tanks for brewing the first batches of experimental vaccine, international concern is bubbling about what countries will get the first inoculations.

The Baltimore plant is the second of four planned locations around the world where Johnson & Johnson plans to pump out vaccine on a massive scale, months before testing the first dose in a human being. The manufacturing head start is one part of a worldwide scramble to protect the human population from the virus, which is not expected to vanish on its own.

If SARS-CoV-2 establishes itself as a stubborn, endemic virus akin to influenza, medical experts say, there almost certainly will not be enough vaccine for at least several years, even with the unprecedented effort to manufacture billions of doses. About 70 percent of the world’s population — or 5.6 billion people — will probably need to be inoculated to begin to establish herd immunity and slow its spread, scientists say.

Yet the nationalistic priorities of individual nations could thwart the strategic imperative to tamp down hot spots wherever they are on the planet — including poor countries that cannot afford the vaccine. The United States in particular could be left in the cold if vaccines developed here as part of a go-it-alone approach turn out to be less effective than those produced in China or Europe.

The scenario public health experts fear most is a worldwide fight in which manufacturers sell only to the highest bidders, rich countries try to buy up the supplies, and nations where manufacturers are located hoard vaccines for their own citizens.

“The model of countries thinking only of themselves is not going to work. Even if you’re living somewhere that’s somehow perfectly without any infections, your best efforts to fight the virus are going to fail unless you shut off all your borders and trade,” said Seth Berkley, CEO of Gavi, a public-private partnership that helps provide vaccines to developing countries. “This is a global problem that requires a global solution.”

International health advocates want to avoid a repeat of 2009, when wealthy countries — including the United States, which was led by the internationalist-leaning Barack Obama — were at the head of the line for H1N1 swine-flu vaccine, leaving underdeveloped countries with little supply until after the pandemic subsided.

Such an approach will be sorely tested by President Trump and other world leaders with nationalistic impulses and their own anxious populations that want to reduce the deadly threat and bring their economies back to life.

In the United States, the federal government agency in charge of emergency vaccine development indicated it is prioritizing domestic concerns — an “America First” mentality that has shaped much of the Trump administration’s pandemic response.

“Right now, we’re focused on the whole-of-America approach required to expedite the availability of vaccines,” Gary Disbrow, acting director of the Biomedical Advanced Research and Development Authority (BARDA), said in an emailed response to written questions from The Washington Post.

BARDA, tasked with protecting Americans from biological threats, is channeling nearly half a billion dollars in emergency funds to Johnson & Johnson to develop a vaccine. It also is providing hundreds of millions of dollars in financial support for vaccine efforts by Sanofi, the large French drug company, and Moderna, a biotech company in Massachusetts teaming with a Swiss company for vaccine manufacturing.

“By working with multiple companies, we have more ‘shots on goal’ to increase the chances that the U.S. will have one or more vaccines available as quickly as possible,” Disbrow said.

The global grab for protective equipment and ventilators that left poorer countries empty-handed suggests the competition over vaccines could be at least as fierce. Dozens of companies large and small are rushing to develop vaccines using different technologies and approaches. Avalere Health, a healthcare consulting company, is tracking at least 120 vaccine projects sponsored by governments, universities, nonprofit institutes and private companies.

Large-scale manufacturing capacity will be required to produce viable products out of those experiments and clinical trials. Some vaccines may require two doses, putting greater pressure on manufacturing capacity.

Some top officials in the Trump administration are raising attention to the issue. Francis S. Collins, the director of the National Institutes of Health, and Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, both physicians, were co-authors of an article published in the journal Science on Monday that urged international coordination.

“Cost, distribution system, cold-chain requirements, and delivery of widespread coverage are all potential constriction points in the eventual delivery of vaccines to individuals and communities,” they wrote. “All of these issues require global cooperation among organizations involved in health care delivery and economics.”

Recognizing the financial and logistical bottlenecks for smaller biotech companies, Bill Gates, the philanthropist and Microsoft founder, announced in April on “The Daily Show With Trevor Noah” that the Bill and Melinda Gates Foundation would make billions of dollars available to help seven undisclosed companies build out manufacturing capacity.

The race for a vaccine is full of risks, because no one knows which projects will succeed. That forces companies to scale up to produce millions of doses of vaccine that might end up being worthless.

Another risk: The United States might not be well positioned if the best vaccines end up coming from other countries or international collaborations — such as a development and manufacturing cooperative that world leaders pledged billions toward this month at an online event the Trump administration skipped. A Trump administration official said this month that the United States supports such efforts despite skipping the pledge event.

Jeremy Konyndyk, a senior policy fellow at the Center for Global Development who worked on the U.S. government’s response to international disasters in the Obama administration, said that “we need to lay the groundwork for global vaccine sharing now, before we know who is the winner.”

“It’s basically negotiated — there’s not a global framework or protocol, there’s not a preexisting framework about how to do this,” Konyndyk said. “What we don’t want is a situation of haves and have-nots, based on either who gets vaccine to work or who has the production capacity or who has the wealth.”

Much of the international outrage during the H1N1 swine-flu pandemic 11 years ago centered on supply contracts Western governments secured with vaccine manufacturers. The United States, under President Obama, had contracts in 2009 that entitled it to 600 million doses, The Post reported at the time, a huge share of potential global supply.

Stronger frameworks for international planning have since been established for influenza vaccines. But those frameworks do not automatically apply to the coronavirus. David Fidler, adjunct senior fellow for cybersecurity and global health at the Council on Foreign Relations and a visiting professor at the Washington University School of Law in St. Louis, said the much larger threat of the coronavirus could make it more difficult for countries to act together — and especially difficult for the United States, which has experienced the highest coronavirus caseload and death toll in the world.

“Access to vaccine, as a safety valve to release that political and economic pressure, is going to be astronomical for anyone who is in the White House,” Fidler said. “That pressure is not going to dissipate if Joe Biden wins in November.”

Large drug companies may enter into vaccine contracts again as they face pressure to recoup their investments, he added.

“For pharmaceutical companies that make vaccines, your best customers for return on investment are high-income countries,” Fidler said. “If you’re going to get a return on investment, somebody has to buy it.”

According to data from the Centers for Disease Control and Prevention, more than 80 million Americans were inoculated in the 2009 swine-flu pandemic — an amount that roughly equals the total number of doses that were received in 77 countries under a distribution plan organized by the World Health Organization.

“Rich countries monopolized the vaccine, poor countries were left behind,” Gavin Yamey, director of the Center for Policy Impact in Global Health at Duke University, said in a university podcast. “They got the vaccine later, and they got less of it.” Allowing a repeat scenario in the battle against the coronavirus would be a devastating mistake, he said.

“Unless we make this vaccine globally available,” he said, “we are not going to be able to end the pandemic, because … an outbreak anywhere is an outbreak everywhere.”

BARDA has not yet signed contracts with Johnson & Johnson or other companies for delivery of specific numbers of doses, a step Disbrow said would be “premature at this point.”

Johnson & Johnson “has indicated that approximately 300 million doses of vaccine would be available in the U.S. each year,” Disbrow said, which would be enough to vaccinate 90 percent of the U.S. population of 330 million people. That number of doses matches up with the projected annual capacity at the Baltimore plant, which is operated by a publicly traded corporation called Emergent BioSolutions and receives funding as one of four federal locations designated a Center for Innovation in Advanced Development and Manufacturing.

Asked about Disbrow’s assertion, a top executive at Johnson & Johnson did not commit to specific volumes or timing of delivery of vaccine in the United States, citing the need to evaluate global priorities to stop the pandemic.

The company wants to produce 1 billion doses by the end of 2021, making the first doses available as early as this winter. Where vaccine will be most needed is not known, although health-care workers will be a high priority, Paul Stoffels, Johnson & Johnson’s executive vice president and chief scientific officer, said in an interview.

Stoffels said Johnson & Johnson is committed to satisfying demand wherever it is most needed. The company also is not interested in making a profit on the coronavirus vaccine, he said.

“It’s very difficult to determine at the moment where the epidemic is then going to be,” Stoffels said. “We think honestly … that the priority should go to the people who need it most — first, that are probably the health-care workers and people at high risk, and maybe wherever they are in the world.”

“On the one hand, we work very much with the U.S.,” he added, “but on the other hand we also do our best to make sure we can serve the world.”

Johnson & Johnson says its vaccine technology is particularly well suited to underdeveloped regions because vials of doses can be shipped at relatively warm temperatures in the last stage of delivery. In addition to Baltimore, it will be producing a vaccine at its plant in the Netherlands and is looking for at least two other locations in Asia and Europe, according to the company. It also is contracting with glass-vial manufacturers to buy five-dose vials to ease shortages of packaging, Stoffels said.

Pfizer, which is testing multiple vaccine candidates, has identified factories in the United States and Belgium and is securing its supply chain, with the goal of having 10 million to 20 million doses available by fall and hundreds of millions of doses next year, the company said.

“We’re thinking completely outside of what is, quote-unquote, normal,” said Kathrin Jansen, head of vaccine research and development for Pfizer. “We come up with unique approaches, we’re getting into contract negotiations with suppliers, and we haven’t seen a single clinical data point. It’s unheard of.”

Pfizer’s vaccine, being developed with the German company BioNTech, contains genetic material encapsulated in a fat droplet made of four lipids. Before it even knew which vaccine would move forward, Pfizer had to secure enough of each of those lipids. Pfizer managers need enzymes to make the genetic material, called RNA, so they had to find suppliers and secure enough supply for their anticipated demand.

Layered on top of the logistical supply chain is scientific uncertainty. Pfizer’s planning scenario is built on a “worst-case prediction” that the vaccine it ends up making will be the one that requires the highest dose. If the company succeeds with a different version — one that makes copies of itself once inside cells and thus is effective at about a tenth of the dose — Pfizer could be thinking about billions of doses as opposed to hundreds of millions.

“All those are wild cards, and the whole planning right now needs a certain amount of flexibility,” Jansen said. “We don’t want to have too little capacity. We don’t want to have too much capacity. We don’t know how much we need. It’s a very interesting dance going on right now to get it right, and none of us has ever done this.”

Jansen said that the global community will have to figure out how to distribute vaccine equitably through the world, through organizations such as the WHO. She did not say where Pfizer’s vaccines would go.

“I think by the time we will face the issue, I’m very confident there will be plans in place, to make sure that there’s an equitable rollout,” Jansen said.

Moderna has a factory in a suburb south of Boston capable of producing 100 million doses in a year. This month, the company announced a 10-year partnership with Lonza, a Swiss contract development and manufacturing company that will help it scale up production, with the goal of beginning manufacturing in July. The partnership could expand manufacturing capabilities to 1 billion doses a year.

Stéphane Bancel, chief executive of Moderna, said he hopes governments will place large orders with companies such as his before the products are formally approved — so that they can spend the next 12 to 18 months making as much vaccine as they can, to be ready for the surge in demand if and when they get the regulatory go-ahead.

“If we start stockpiling now,” he said, “all the products we make between now and launch are available the day of launch.”

Clarification: An earlier version of this story referred to Avalere Health as a pharmaceutical consulting company. It is a healthcare consulting company.