The U.S. celebrated when new coronavirus vaccines were developed at record-breaking speed. And in December the candidates from Pfizer and BioNTech and Moderna were quickly approved for emergency use by the Food and Drug Administration. But two months later, only 10 percent of Americans have received at least one shot. And fewer than 3 percent of them have received both of the necessary doses. Many feel frustrated with the slow distribution process and confused about how to sign up for shots. What exactly is making all this take so long?

The process starts with manufacturers producing vaccines and storing them in specialized glass vials that each hold several doses. These vials are shipped from the manufacturing facility itself (in the case of Pfizer) or from a distribution center run by the McKesson Corporation on behalf of the federal government (in the case of Moderna). When each batch is ready, the distributors notify the federal government so officials know how many doses are available to be shipped and can allocate them throughout the country by states, territories or even individual cities. Each of these jurisdictions decides how to distribute the vaccine, it and notifies individual health care providers as to how much they can expect to receive and when. Then the jurisdiction can submit its distribution order to the federal system, which passes the information to Pfizer or McKesson so the company knows where to ship the vaccines. Once the local health providers—including pharmacies, hospitals and nursing homes—receive their vials, they can administer doses, record the immunizations and submit this information to the Centers for Disease Control and Prevention.

Any delay in this chain can slow down distribution. “There is a long laundry list of things that could go wrong in these, and it’s like Murphy’s Law: if something can go wrong, it usually goes wrong,” says Jennifer Pancorbo, director of industry programs and research at North Carolina State University’s Biomanufacturing Training and Education Center.

Demanding Supplies

One of the main potential bottlenecks occurs right at the beginning of the process: a simple lack of sufficient ingredients. The FDA has only approved two vaccines for emergency use, and both rely on messenger RNA (mRNA) technology. “This vaccine is fairly new; the design is very cutting edge,” Pancorbo notes. Although researchers had created mRNA vaccines on a small scale, companies now must churn out enough for a worldwide vaccination campaign. “We have never had the need of this massive scale of production that we do now,” Pancorbo says. This has left companies scrambling to obtain required materials, including plasmids—the genetic templates used to produce the needed mRNA—as well as mRNA building blocks such as nucleotides and enzymes. “All these components that are necessary to make the vaccine are not necessarily available at the scale that we need right now,” she says.

Crucial equipment is also in short supply, says Glenn Richey, chair of the department of supply chain management at Auburn University’s Harbert College of Business. “We’re seeing issues with the production of vials and syringes and those types of things that actually move the product from the storage container to the person,” he explains. This will be an ongoing concern, Richey adds, as companies try to create the hundreds of millions of doses that will be necessary for the U.S. population to reach herd immunity. “We do see companies stepping up the pace and producing these things, but as we expand out to the larger population, we’re going to need more and more,” he says.

One way to speed things up would be to start producing different types of vaccines, and several new candidates have shown promising results. Because these vaccines rely on mechanisms other than mRNA, they may not have as many supply-chain problems as the mRNA versions. Johnson & Johnson has applied to the FDA for emergency-use authorization for its vaccine, which requires only a single shot and has less stringent refrigeration requirements than those based on mRNA.

Shots in Arms

In addition to limitations on how fast companies can produce vaccines, the CDC’s public data reveal a consistent lag between the number of doses shipped and the number actually administered. But Julie Swann, a professor and head of the department of industrial and systems engineering at North Carolina State University, points out that it simply takes time for records of administered doses to catch up. “If you think, ‘Two days to ship, three days to give it out, and another two days to record that,’ there can easily be a week between when the federal government says this has been distributed and when you can really expect to see that number [of administered doses] change correspondingly,” she says. Although vaccines must be shipped as part of a “cold chain” process that requires specialized packaging, dry ice and prompt delivery, Swann suggests that transportation is not the issue. “It’s not like you can fly the vaccine instead of drive the vaccine, and then this gap will disappear,” she says. Instead Swann points to inefficiencies in the next step of the process: physically getting the most vulnerable people to places where shots can be administered.

States are coordinating the actual administration of vaccines on their own. “We’ve got 50 states and 50 different plans. We do not have a single coordinated policy in terms of how this should be done optimally, so it’s the left to the states,” says Christopher Gill, an associate professor of global health at Boston University’s School of Public Health. His own state of Massachusetts, for example, has a carefully tiered priority plan—but implementing it has been difficult because doing so requires organizations to bring in the right number of people with the appropriate priority status. “The system starts to back up,” Gill says, “because you can’t find the people who are supposed to fit into those categories, and so nobody gets access or doses are not being used at the end of each day.”

Still, many experts agree that scrapping priority rankings is not the answer. Doing so would certainly speed up the vaccination rate but would also risk making the whole rollout less fair and efficient. “Even now the goal is not ‘Give it to as many people as possible,’” Swann says, noting that many of the recipients in such a scenario would be at low risk of spreading the disease or of developing a severe case. “You could very efficiently, very quickly, give out the vaccine in ways that do not prevent the most deaths or hospitalizations.”

Instead the last step of the distribution process might be improved by using better tools for making reservations. “They haven’t been doing a great job, in a lot of states, in terms of queuing folks to get the vaccine,” Richey says. “They really probably ought to be doing some type of reservation system.” Other experts agree. “Imagine, Swann suggests, “that instead of hundreds and thousands of people calling around to get vaccines, that each state had a waiting list where you go, and you put in some of your information—‘I’m 65 years old,’ ‘I have diabetes,’ ‘I teach in a classroom,’ whatever these things are—and that every time there’s a new set of vaccines that are shipped out, that is announced first to people on the waiting list based on their priority.”

In the absence of such tools, Swann cautions people to temper their expectations of when they will actually receive a shot. “I say summer would be the earliest that someone with no other [priority group] characteristics might have access to the vaccine,” she says. “Get it in your head so that you mentally prepare yourself.” Richey is a little more optimistic about the potential for distribution bottlenecks to ease as the vaccination process continues. “It’s good to think that every day, it gets a little bit better,” he says. “Every day, a few more people are vaccinated.”

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