How Pfizer Makes Its Covid-19 Vaccine

How Pfizer Makes Its Covid-19 Vaccine

At this facility in Chesterfield, Missouri, trillions of bacteria produce tiny loops of DNA that contain coronavirus genes – the raw material for the Pfizer BioNTech vaccine.

This is the beginning of a complex manufacturing and testing process that takes 60 days and involves Pfizer facilities in three states. The result will be millions of doses of the vaccine, frozen and ready to ship.


Pulling DNA from the cold store

A scientist removes vials of DNA from the main cell bank, the source of every batch of Pfizer's Covid-19 vaccine. The vials are kept at -150 ° C. (–238 ° F) or below and contain small rings of DNA called plasmids.


Spike protein



Spike proteins


Spike protein



Spike proteins

Each plasmid contains a coronavirus gene, the genetic instructions for a human cell to make coronavirus proteins and trigger an immune response to the virus.

“This species reminds me of September 11th. It's the same feeling of: what were you doing back then? "– Amy Barnessenior scientist

Scientists thaw the plasmids and modify a batch of E. coli bacteria to incorporate the plasmids into their cells.

A single vial can eventually produce up to 50 million doses of the vaccine.


Grow the cells

"Rarely do you work on something in the lab and go home and turn on your television and see that the top 10 headlines are what you were working on today."– Katherine Calhounassociate scientist

The vial of modified bacteria is swirled in a flask of amber growth medium, a sterile and warm environment that encourages the bacteria to multiply.


Ferment the mixture

The bacteria can grow overnight and are then transferred to a large fermenter that contains up to 300 liters of a nutrient broth.

The bacterial broth spends four days in the fermenter, multiplies every 20 minutes and makes trillions of copies of the DNA plasmids.


Harvest and purify the DNA

When the fermentation is complete, scientists add chemicals to break up the bacteria and release the plasmids from their enclosing cells.

The mixture is then purified to remove the bacteria and leave only the plasmids.


Test of quality

The plasmids are tested for purity and compared to previous samples to confirm that the coronavirus gene sequence has not changed.

Linear DNA

for comparison


Cut the plasmids

When the plasmids pass the quality tests, proteins called enzymes are added to the mixture. The enzymes cut the circular plasmids and separate the coronavirus genes into straight segments, a process called linearization that takes about two days.


Cutting the



Cutting the



Filter the DNA

Remaining bacteria or plasmid fragments are filtered out, leaving 1 liter bottles of purified DNA.

The DNA sequences are retested and serve as templates for the next stage of the process. Each bottle of DNA produces approximately 1.5 million doses of the vaccine.

The Chesterfield facility is Pfizer's only source of plasmid for the Covid-19 vaccine. However, completing the vaccine will require several more steps at two other facilities.


Freeze, pack and ship

Each bottle of DNA is frozen, packaged, sealed and packaged with a small monitor that records the temperature during transport.

“What we do is so important because we basically control everything that is shipped. Every vial that goes to every person goes through us first. "– Sahar GholamiLaboratory technician

Up to 48 bottles are packed in a container with enough dry ice to keep them frozen –20 ° C. (-4 ° F). The containers are sealed to prevent tampering and are shipped to a Pfizer research and manufacturing facility in Andover, Massachusetts.

The Andover plant processes the DNA into messenger RNA or mRNA, the active ingredient in the Pfizer BioNTech vaccine.

Other bottles are flown to BioNTech plants in Mainz, where they are processed for Europe and other markets.


Transcribe the DNA into mRNA

In the Andover facility, yellow walls mark the mRNA suite. Five bottles of DNA are thawed for a day and then mixed with the building blocks of messenger RNA.

Over several hours, enzymes open the DNA templates and transcribe them into strands of mRNA. The finished vaccine transports the mRNA into human cells, which read the coronavirus gene and start producing coronavirus proteins.




DNA in


The mixture is placed in a storage container and then filtered to remove unwanted DNA, enzymes, or other contaminants. Each batch will eventually yield up to 7.5 million doses of the vaccine.


Test the mRNA

"This new RNA lipid nanoparticle was new to us, but we were able to take our tried and tested tools out and understand, analyze and figure out how to make it high quality."– Meg RueschVice President for Research and Development

The Pfizer BioNTech vaccine was the first mRNA vaccine approved for use in human emergencies.

Analysts repeatedly test the filtered mRNA to check its purity and to confirm that the genetic sequence is correct.

The result is 10 bags of coronavirus mRNA. Each bag holds 16 liters and is the raw material for around 750,000 doses of the vaccine.


Freeze, pack and ship (again)

The bags with mRNA are frozen –20 ° C. (-4 ° F) and shipped to a Pfizer facility in Kalamazoo, Michigan, where they are processed into the finished vaccine and packaged into vials. The samples are also returned to Pfizer's Chesterfield facility for retesting.

The Andover facility can produce two batches of mRNA per week of around 10 sachets each. The facility ran its first batch of tests last July and recently doubled its mRNA capacity by adding a second suite.

A parallel process in Mainz, Germany processes DNA from the Chesterfield plant and sends bags of filtered mRNA to Puurs, Belgium.


Prepare the mRNA

"There are no weekend breaks. There are no spaces in the project schedule. You hire people, you hire everyone you can. However, the quality is the same as any vaccine."– Meg RueschVice President for Research and Development

The Kalamazoo facility receives the bags of mRNA, keeps them frozen until needed, and then thaws enough to produce 3.6 million doses of the vaccine, or 600,000 vials.

The thawed mRNA is mixed with water in preparation for the manufacture of the vaccine.


Prepare the lipids

In a separate process, the scientists prepare the oily lipids that protect the mRNA and help it penetrate human cells.

The lipids are measured out and mixed with ethanol, which is eventually removed from the finished vaccine.


Assemble the mRNA vaccine

"This is where the magic happens."– Patrick McEvoySenior Director of Operation and technology

A rack with 16 pumps precisely controls the flow of the mRNA and lipid solutions and then mixes them together to form lipid nanoparticles.

When the lipids come into contact with the bare mRNA strands, an electrical charge pulls them together in a nanosecond. The mRNA is surrounded by several lipid layers and forms an oily, protective vaccine particle.

Synchronizing eight pairs of pumps is not an ideal solution, but Pfizer engineers chose to scale the existing technology instead of trying to build a larger, untested precision mixer.

The newly prepared vaccine is filtered to remove the ethanol, concentrated and filtered again to remove any impurities, and finally sterilized.


Prepare the vials

“We make hundreds of millions of cans of product for many people. It's a great responsibility and we take it very, very seriously. "– Chaz CalitriVice President of Operations

Hundreds of thousands of empty vials are washed and heat sterilized.

A set of 13 cameras perform a high speed visual inspection and take more than 100 photos of each vial. All vials with cracks, chips, or other defects are removed from the line.

A separate machine places each vial under vacuum to ensure that it does not leak.


Hurry up to fill the vials

"It's like a relay race."– Patrick McEvoySenior Director of Operation and technology

The flow of the vials is restricted to a single line. Machines inject 0.45 ml of a concentrated vaccine solution into each vial, enough for six doses after dilution. The vials are sealed with foil and closed with purple lids at a rate of up to 575 vials per minute. (The footage above shows a test run with empty vials.)

The vaccine is refrigerated, but it heats up quickly during the filling process and the mRNA will degrade if it is not frozen for too long. Kalamazoo only has a limited time of about 46 hours to put the liquid vaccine in vials and then in the freezer.


Package, freeze and test

The filled bottles are inspected again and then labeled and packed in “pizza boxes”, small plastic dishes with 195 bottles each.

The trays are bundled in stacks of five and loaded into one of 350 industrial freezers. Each freezer holds 300 trays.

President Joe Biden watches vaccine trays refrigerate at Pfizer's Kalamazoo facility on February 19. Doug Mills / The New York Times

It will take a few days for the vaccine to reach the vaccine -70 ° C. (–94 ° F) Required for long-term storage, every freezer is tested to ensure that every shelf can sustain this ultra-cold temperature.

After freezing, the vaccine bottles are tested for four weeks. Samples are returned to the Andover facility where the mRNA was produced and to the Chesterfield site where the DNA templates were provided.

Pfizer currently operates on a 60-day timeline from start to finish, and more than half of that time is devoted to testing.


Pack and ship the finished vaccine

After weeks of testing, the vaccine is ready to be shipped. Workers pull trays out of the freezers and pack them in shipping boxes with temperature and position sensors. The minimum order quantity is one tray of 195 vials and one box holds up to five trays.

Each box contains 45 pounds of dry ice – enough that Pfizer's Kalamazoo facility is now producing dry ice on site. Pfizer is also evaluating various formulations of the vaccine, including freeze-dried and ready-to-use versions that would not require ultra-cold storage.

Commercial production of the vaccine began in September. By April 22, the facility had shipped more than 150 million doses of vaccine to the United States. Pfizer expects to dispose of 220 million doses by the end of May and 300 million doses by mid-July.


Give the vaccine

“I saw on the news that they were going to put these mass vaccination sites in place, but they needed nurses because they were small. And I thought I have to go. I have to go help. "– Jacquelyn ChartierNurse vaccine

Around 141 million people in the United States – more than half of the country's adults – have received at least one dose of a Covid-19 vaccine. More than a billion doses have been administered worldwide.

The city of Los Angeles is home to a mass vaccination site upstairs at Dodger Stadium. On February 5, health care workers gave thousands of recordings of the Moderna vaccine, which also uses mRNA to build immunity. (Moderna declined to allow film access to their facilities.)

Johnson & Johnson's single-dose vaccine uses an adenovirus to deliver DNA into human cells. A Baltimore facility operated by Emergent BioSolutions had to dispense up to 15 million doses of Johnson & Johnson's vaccine due to possible contamination.


A vaccine against variants

Many of the coronavirus variants currently in circulation have key mutations in their spike proteins that help the virus bind more tightly to human cells or evade certain types of antibodies.

Pfizer and BioNTech are developing and testing new versions of their vaccine against newer variants and could potentially change their genetic recipe to mass-produce Covid-19 vaccines that target specific variants.

















To that end, Pfizer returned where vaccine production began, to the master cell bank in Chesterfield, which keeps rings of DNA frozen.

A new batch of DNA that carries modified coronavirus genes could eventually produce a slightly different vaccine that encourages the immune system to better recognize newer coronavirus mutations.


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