When Bruce Y. Lee was helping the U.S. government model delivery plans for H1N1 influenza vaccines, he came to expect one constant: The schedule would always change.
“We’d constantly have to update the models as new production numbers came out,” said Lee, a professor at CUNY Graduate School of Public Health & Health Policy, who developed computational models to guide the national response to the H1N1 flu pandemic in 2009. “That just became accepted.”
The shifting timelines are already apparent with COVID-19 vaccine distribution in the U.S. — even before the rollout starts in the coming days. The Trump administration declared in May that 300 million vaccine doses would be available by January 2021, with the first distributed in October of this year. By October, that had shifted to 100 million doses by the end of the year, according to U.S. Health and Human Services Secretary Alex Azar. Currently, the plan is for 40 million doses to be distributed in December, though some in health care are skeptical of even that prediction.
Pharmaceutical and vaccine production involves complex coordination, involving product development, manufacturing, packaging, storage, distribution, and regulatory review, and each stage can cause unexpected delays.
The manufacturing process can — and usually does — go awry at some point. “Manufacturing never goes 100%, there’s always issues and stock you have to throw out,” said Lee. “You bake a thousand cakes, you’re not going to get a thousand successful cakes.”
At every stage of production, manufacturers must test the product to show that each batch, from each different facility, is equivalent to the original. This will inevitably reveal issues that need addressing as COVID-19 vaccines are produced at unprecedented scale and speed. “Not only do we want it yesterday, but we need a lot of it yesterday,” said Thomas Denny, chief operating officer of the Duke Human Vaccine Institute. “If you try and do something quickly in your kitchen, even if you have a recipe, sometimes things go wrong.”
Every feature of the final vaccine, including buffers, glass, pipette tips, dry ice, and packaging, then comes with its own potential production issues. Pfizer recently had to cut its end-of-year supply projections for COVID-19 vaccines in half, because of delays in scaling up the raw material supply chain.
As more vaccines are rolled out, this will increase the pressure on available supplies. “You’re dealing with a limited supply chain,” said Denny. “I would not be surprised, as we get two or three vaccines being manufactured, if we see some challenges.”
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— Olivia Goldhill, STAT