Hospitals and clinics across the country are canceling vaccine appointments because the Trump administration tells states how many doses they’ll receive only one week at a time, making it all but impossible to plan a comprehensive vaccination campaign.

The decision to go week by week was made by Operation Warp Speed’s chief operating officer, Gen. Gustave Perna, because he didn’t want to count on supplies before they were ready. Overly optimistic production forecasts turned out to be a major disappointment in the rollout of the H1N1 vaccine more than a decade ago, also leading to canceled appointments and widespread frustrations with the government’s messaging.

This time, however, the most pressing problem isn’t the overpromising of supply. For each of the past three weeks, the federal government got about 4.3 million shots. But the amount that each state is sent has fluctuated as Operation Warp Speed changes the quantities available week by week.

State health officials say the unpredictable shipments have led to chaos on the ground, including the inability to quickly use up all of the doses sent to them. The week-by-week system also makes it hard to plan for the second doses that everyone needs because they come three or four weeks after the initial dose.

“It’s a huge problem. When you’re setting up clinics and registration systems, you have to have some idea of the supply,” said Lori Freeman, chief executive officer of the National Association of County and City Health Officials. “If you’re starting and stopping all the time, it can lead to confusion in the community — they’ll think you don’t know what you’re doing.”

As President-elect Joe Biden’s team prepares to take over on Wednesday, officials are aware of the problem and will have to decide how to address it, according to a member of the transition team. Sorting it out will be critical to meeting Biden’s goal of 100 million vaccinations in his first 100 days.

In the meantime, many Americans are experiencing this problem firsthand in the form of canceled appointments. On Jan. 14, Mount Sinai Health System sent a flurry of emails out to elderly patients across New York City, just two days after expanding eligibility to New Yorkers ages 65 and up. “You are receiving this email because you are scheduled for a vaccine appointment. … Unfortunately, your appointment has been cancelled due to a sudden decrease in the amount of COVID-19 vaccine being supplied to us,” the email said. “We are truly sorry, but unfortunately, the vaccine supply is not under our control.”

In Virginia, allocations to the state Department of Health vary not only week to week, but day to day. Dr. Danny Avula, Virginia’s COVID-19 vaccine coordinator, said the department learned in the middle of last week that it could get up to 80,000 doses, but — for reasons unclear to the Virginia team — the allocation increased to 106,000 by Thursday when it went to place orders. The state agency has tried to give local health providers consistent information about how many doses they’ll receive at their clinics and hospitals, but Avula said state officials will have to instead explain the erratic allocations.

“States don’t know what they will get week to week,” said Dr. Marcus Plescia, chief medical officer of the Association of State and Territorial Health Officials. “The locals get frustrated with states, thinking the states have all this information, but the states are in the same position as the locals.”

The way that Operation Warp Speed leaves it up to states to hand out vaccines within their borders harks back to the Trump administration’s strategy of passing down responsibility during earlier phases of pandemic response. In April, White House adviser Jared Kushner chided governors for seeking help from the federal government’s stockpile of emergency medical supplies. And President Donald Trump left states to decide how to reopen their economies, telling governors, “You’re going to call your own shots.”

The root of the problem now is the system designed around weekly allotments. Perna has said he set up the system this way because he wanted to act on only supplies in hand, not predictions.

“Every week I get an update, I know exactly what has been approved by the FDA for final distribution,” he explained in a Dec. 12 briefing. “I will not allow those estimates to go forward for speculation because I want people to focus on what is actually available.”

The makers of the two authorized vaccines, Pfizer and Moderna, are each contracted to supply 100 million doses by the end of March. But with just 31.2 million delivered as of Jan. 15, according to data from the Centers for Disease Control and Prevention, the companies will need to ramp up their pace to hit their targets.

The companies give the federal government weekly or daily updates on their production numbers, according to their contracts. Then Operation Warp Speed takes the total number of available Pfizer and Moderna doses for the week and divides them up between the states. The allocations are currently based on the state’s population over age 18, but the Trump administration said last week it would soon change the formula to be based on each state’s elderly population and ongoing pace of vaccinations. That change hasn’t taken effect yet, and the new administration may not decide to stick with it.

Every Tuesday, these state-by-state allocations are keyed into a software system called Tiberius, which was built for the government by the data analysis company Palantir. (Tiberius is the middle name of Star Trek’s Capt. James T. Kirk; “Warp Speed” is also a Star Trek reference.) The numbers show up on states’ screens around noon Eastern time, according to Oregon health authority spokesperson Jonathan Modie.

But these allocations aren’t final: Adjustments are made that can result in further daily changes. The system subtracts out doses that are set aside for long-term care facilities, which are administered by Walgreens and CVS, as well as “any corrections from the prior week, including doses that weren’t ordered by states in previous weeks, or doses shipped to states accidentally that CDC needs paid back,” explained Modie. Only then is a maximum order “cap” calculated for the week, which is placed into a separate system, called VTrckS.

Perna publicly apologized in December when states received fewer doses than he’d told them to expect. The general said at the time that the discrepancy was a one-time mistake that resulted from moving the releases from Fridays to Tuesdays. “This is a herculean effort and we are not perfect,” he said. “It looked very good on paper. Paper plans are very good. Execution is where we learn and we adapt it.”

But the problem of unpredictable numbers has persisted as states continue to grapple with last-minute adjustments to their allocations.

For this coming week, Michigan was initially told on Tuesday it was receiving 62,400 doses of the Pfizer vaccine to distribute among vaccination sites, according to Lynn Sutfin, spokesperson for the state’s Department of Health and Human Services. Then on Wednesday, Michigan was told that an additional 60,000 doses of the Moderna vaccine that were initially earmarked for long-term care facilities were available for general vaccination sites instead. On one hand, that was good news, because the state got twice as many doses to give out, since the long-term care program wasn’t ready to use them. On the other, this meant the Michigan department had only a day to figure out where to send the extra doses.

The states are responsible for deciding how to distribute their doses to local vaccination sites, and they usually have only two days to figure that out. After receiving their allocations on Tuesday, each jurisdiction must then submit its orders in VTrckS by Thursday. Shipments arrive the following week.

Second doses are ordered separately, on Sundays, according to a spokesperson from the Department of Health and Human Services, the government agency that houses Operation Warp Speed.

“For the past three weeks, jurisdiction allocations have remained relatively steady around 4.3 million total doses (or just over 2 million first doses) of both Pfizer and Moderna, which has provided additional predictability,” the HHS spokesperson said. “Operation Warp Speed is committed to providing as much planning time as possible, while balancing manufacturing schedules and maximizing doses available.”

Pfizer and Moderna declined to comment on what production numbers they shared with the government program during their regular updates. (Paul Sagan, board chairman of ProPublica, is a member of Moderna’s board.)

Despite stable total doses at the national level in recent weeks, individual states still don’t know what to expect from Operation Warp Speed more than a week ahead, creating continued chaos on the ground.

In Columbus, Ohio, health commissioner Dr. Mysheika Roberts was feeling both encouraged and concerned about the vaccine rollout in her city. It had gotten off to a slow start with the holidays, but after some outreach efforts, the vaccine clinic was steadily booking all 700 slots it had each day. Then, she had a new problem. She was starting to run out of vaccines. “What we have on hand will run out by the end of day Wednesday,” she said in a Monday interview. “We’re just calling the state and telling them we need more. We’re potentially going to have to cancel clinics on the 14th, 15th, 16th.” Roberts was saved from having to cancel appointments because the state managed to send her more shots at the last minute, according to a spokesperson, but the site’s supply is once again limited, so the cycle is beginning again.

Starting Wednesday, it will be up to the Biden administration to provide clear visibility for states, according to a member of the president-elect’s COVID-19 team, who asked not to be identified because he wasn’t authorized to speak on behalf of the new administration.

“The government can point at the manufacturer, but it’s like asking the [Defense Department], ‘How many planes do you have?’ and them saying, ‘I don’t know, ask Boeing,’” the person said.

It’s critical for the government to know how many doses are available at any given time and how many are coming through the pipeline, the person added. “How can this not be known?” he said. “It’s the most basic question.”