Cómo fabrica Pfizer su vacuna para la COVID-19

How Pfizer Makes Its Covid-19 Vaccine

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

It is the beginning of a complex 60-day manufacturing and testing process involving Pfizer facilities in three states. The result will be millions of doses of the vaccine, frozen and ready to ship.


Take the DNA out of the freezer

A scientist extracts DNA vials from the master cell bank, which is the source for each batch of Pfizer's COVID-19 vaccine. The vials are held at -150 ° C. or less and contain small rings of DNA called plasmids.

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Tip of


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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. The same feeling of: what were you doing in that moment? "– Amy BarnesSENIOR SCIENTIST

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

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


Cultivate cells

"You rarely work on anything in the lab and when you get home you turn on the television and see that the top ten headlines are what you were working on today."– Katherine CalhounASSOCIATED SCIENTIST

The modified bacterial vial is placed in a flask with amber growth medium, a warm, sterile environment that encourages bacteria to multiply.


of bacteria


of bacteria


Fermentation of 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.


of bacteria


of bacteria

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


Collect and purify DNA

After the fermentation is complete, the scientists add chemicals to break down the bacteria and release the plasmids from the cells that contain them.

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


Quality inspection

Plasmids are checked for purity and compared to previous samples to confirm that the coronavirus gene sequence has not changed.

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the protein


Linear DNA

for comparison

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Cut the plasmids

When the plasmids pass quality controls, 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.

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Enzymes that

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Filter the DNA

Any remaining bacteria or plasmid fragments are filtered, 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 DNA vial is frozen, packaged, sealed and packed with a small monitor that records the temperature during transport.

“What we do is very important because we basically control everything that is broadcast. Every bottle that goes to every person goes through us first. "– Sahar GholamiLABORATORY TECHNOLOGY

Up to 48 jars are packed in a container with enough dry ice to keep them frozen –20 ° C.. The containers are locked to prevent tampering and will be shipped to a Pfizer research and manufacturing facility in Andover, Massachusetts.

The Andover plant will process the DNA into messenger RNA or mRNA, the active ingredient in Pfizer-BioNTech's vaccine.

Other bottles are delivered by air to the BioNTech plants in Mainz, where they are processed for Europe and other markets.


Transcribe DNA into mRNA

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

Over several hours, the enzymes open the DNA templates and transcribe them into mRNA strands. The finished vaccine delivers the mRNA to human cells, which read the coronavirus gene and begin making proteins from it.





in mRNA

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


Test mRNA

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

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

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

The result is ten pockets of coronavirus mRNA. Each bag contains 16 liters and is the raw material for around 750,000 doses of the vaccine.


Freeze, pack and ship (again)

The mRNA bags are frozen at –20 ° C. and delivered to Pfizer's Kalamazoo, Michigan facility, where they are made into the finished vaccine and packaged in vials. The samples will also be sent to Pfizer's Chesterfield facility for retesting.

The Andover facility can produce two batches of mRNA per week, each containing about ten bags. The facility ran its first batch of tests last July and recently doubled its mRNA capacity by adding a second room.

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


Prepare the mRNA

“There are no weekend breaks. The project plan does not contain any spaces. You hire people, you get everyone you can. But the built-in quality is the same as any vaccine. "– Meg RueschVice President of Investigation and development

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

Thawed mRNA is mixed with water to make the vaccine.


Prepare 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 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 set of 16 pumps precisely controls the flow of mRNA and lipid solutions and then mixes them to create lipid nanoparticles

Lipids that





Lipids that





When lipids come into contact with bare mRNA strands, the electrical charge binds them together in a nanosecond. The mRNA is wrapped in several layers of lipids and forms an oily and protective vaccine.

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

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


Prepare the vials

“We make hundreds of millions of cans of product that go to lots of people. It's a formidable 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 that takes more than 100 photos of each vial. Vials with cracks, chips or other defects are removed from the line.

Each vial is suctioned off by a separate machine to make sure it doesn't leak.


Race to fill the vials

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

The vial flow is reduced to a single line line. The machines inject 0.45 ml of a concentrated vaccine solution into each vial, enough for six doses after dilution. The vials are sealed with aluminum foil and closed with purple caps at a rate of up to 575 vials per minute. (The images above show 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 has a limited time, approximately 46 hours, to put the liquid vaccine in vials and then in the freezer.


Pack, freeze and season to taste

The filled bottles are inspected again, labeled and packed in “pizza boxes”, small plastic bowls with a capacity of 195 bottles each.

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

President Joe Biden watched the vaccine trays enter the refrigerator at the Pfizer facility in Kalamazoo on February 19. Doug Mills / The New York Times

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

Once frozen, the vaccine bottles are stored for four weeks. Samples are delivered to the Andover facility where the mRNA was produced and to the Chesterfield facility where the DNA templates were provided.

Today Pfizer works from start to finish in 60 days, with more than half of that time devoted to testing.


Pack and ship the finished vaccine

After weeks of testing, the vaccine is ready to be shipped. The workers take the 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 20 kilos of dry ice, so Pfizer's Kalamazoo facility is now producing the dry ice on site. Pfizer is also now testing various formulations of the vaccine, including lyophilized and ready-to-use versions that would not require cold storage.

Commercial production of the vaccine began in September. By April 22, the U.S. facility had dispensed more than 150 million doses of vaccines. Pfizer expects to deliver 220 million doses by the end of May and 300 million by mid-July.


Give the vaccine

“I saw on the news that these mass vaccination sites were going to be used, but they needed nurses because they were scarce. And I said to myself: I have to go. I have to go help ”.– Jacquelyn ChartierVaccinate nurse

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

In the city of Los Angeles, there is a mass vaccination center up at Dodger Stadium. On February 5, health workers gave thousands of injections of the Moderna vaccine, which also uses mRNA to build immunity. (Moderna refused to allow access to its facilities for filming.)

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


A vaccine for variants

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

Pfizer and BioNTech are currently 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 this end, Pfizer returned to the place where vaccine production began, the Chesterfield Master Cell Bank, which is used to store frozen rings of DNA.

A new batch of DNA with modified coronavirus genes could produce a slightly different vaccine and encourage the immune system to better recognize newer coronavirus mutations.


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