As the pandemic enters its third year, the COVID-19 vaccines developed by Moderna and Pfizer continue to dominate vaccination efforts in the US. Only 3.34 percent of shots administered in the country have used Johnson & Johnson’s formula. However, many less wealthy nations like Mexico, Vietnam, and Zambia have relied on the J&J shot

On February 8, the New York Times reported that the only facility making usable batches of J&J’s COVID-19 vaccine shut down production and switched to manufacturing a drug for another respiratory virus late last year. The plant, which is located in the Dutch city of Leiden, is expected to resume making the vaccines next month. But the pause raised concerns about accessibility for people in regions where few have been vaccinated against COVID-19. Nearly 40 percent of the world’s population is still unvaccinated, even as more than 92 million Americans have received a booster shot.

“The article came as somewhat of a surprise given that the world has not been vaccinated yet, and that was supposed to be the vaccine that had greater reach out there,” says Deborah Fuller, a vaccinologist at the University of Washington School of Medicine in Seattle. However, she added, the move is not necessarily cause for alarm. The number of COVID-19 shots that have received emergency authorization or full approval around the globe continues to grow. What’s more, there are other kinds of vaccines out there with the same advantages as J&J’s, while being easier to mass produce.

“To stop the pandemic it’s not going to take one type of vaccine, but multiple different types of vaccine that fulfill different sorts of requirements,” Fuller says. “What’s starting to happen with the J&J vaccine is that the unique part of its bubble is shrinking because other things are going to come into play.”

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More than two dozen different COVID-19 vaccines are in use around the world, and more than 100 are being tested in clinical trials. These vaccines use a variety of strategies to train the immune system to recognize and attack the novel coronavirus and its variants. 

Some vaccines, including the ones produced by Moderna and Pfizer, contain genetic material that codes for the spike-shaped protein that helps the virus infect host cells. The recipient’s own cells use these instructions to build copies of the coronavirus protein, which then rouse the immune system without causing disease on their own.

Meanwhile, so-called viral vector vaccines, including those from J&J and the University of Oxford and AstraZeneca’s collaboration, use a different virus engineered to carry the coronavirus genes as a delivery vehicle. Other vaccines contain proteins from the coronavirus or copies of the pathogen that have been weakened or “killed” so they can’t make the recipient sick. Other vaccines contain proteins from the coronavirus, which is also how common immunizations against Hepatitis B and human papillomavirus work. Still others contain copies of the pathogen that have been weakened or “killed,” so they can’t make the recipient sick, much like the chickenpox and inactivated polio vaccines.

“There’s no doubt in my mind that the J&J shot encourages some people who may not have been willing to take the mRNA vaccine early on to at least start getting vaccinated.”

Deborah Fuller, vaccinologist at the University of Washington School of Medicine in Seattle

The mRNA-based shots developed by Moderna and Pfizer have shown the most impressive results when it comes to preventing symptomatic COVID-19. The J&J formulation has also been linked with rare but serious effects. However, all three are very effective at preventing serious illness from Omicron and other variants, Fuller notes. 

The J&J shot also comes with a few advantages of its own. Unlike mRNA vaccines, it doesn’t require ultra-cold storage conditions—and it’s given as a single shot, rather than two shots spaced several weeks apart. These characteristics made the vaccine easier to distribute, particularly to people who lived in remote areas. 

“We have to give J&J credit where it’s due, that it fulfilled an important need very early in the pandemic,” Fuller says. “There’s no doubt in my mind that it saved a lot of people and encouraged some people who may not have been willing to take the mRNA vaccine early on to at least start getting vaccinated.”

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Jake Sargent, a spokesperson for Johnson & Johnson, told the New York Times that the company has millions of doses of the COVID-19 vaccine in inventory and will continue to meet its obligations to organizations that have put in orders on behalf of low-income nations. Lauren Plumer, another spokesperson for the company, also emphasized J&J’s commitment to provide the vaccine to low- and middle-income nations in an email to PopSci. “Global equity has been at the forefront of Johnson & Johnson’s response since the onset of the COVID-19 pandemic,” Plumer wrote. The company continues to work toward a licensing agreement with Aspen Pharmacare in South Africa to allow the group, which currently packages the vaccine, to manufacture and sell it, Plumer added. 

Several protein-based COVID-19 vaccines are already available in Russia, South Korea, the UK, and other countries. A number of other formulations have entered phase 3 clinical trials, including one developed by Sanofi and GSK in the same design as the influenza vaccine Flublok. These immunizations may increasingly fill the same niche as J&J’s shot, Fuller says, making the pause in production less concerning.  

“I’m not as worried about that as I would have been six months ago, when the [protein] vaccines were still some months away from being potentially useful in terms of vaccine distribution,” Fuller says. “That’s a tried and true technology that’s out there. All over the world there are already facilities capable of manufacturing these vaccines locally.”

However, protein-based vaccines take a long time to develop. Researchers use engineered bacteria, yeast, or insect cells to produce the viral proteins. “Then once you produce it, you have to purify it … and then you have to go through quality control to make sure that the structure of the protein is intact,” Fuller says. “It goes through a long process to ensure that it’s a pristine product before it can actually go into people.” 

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These steps aren’t necessary for mRNA and viral vector vaccines, which means they can be developed more swiftly. Because of the lengthy development process for protein-based vaccines, Fuller says, it will be particularly important for vaccine makers to ensure that their formulations provoke a robust immune response that will hold up against Omicron and future variants of the novel coronavirus. Still, she says, as more protein-based shots become available, COVID-19 vaccination rates across the world could rise very quickly.

“We have some exciting new vaccines coming,” Fuller says. “It’s a slow wheel that takes a long time to get going, but once that wheel gets going, that thing just churns out vaccines like nobody’s business.”