Flu Shots, Do You Know How They’re Manufactured?

Flu shots are recommended to us every Fall as a way to protect us against the flu during the winter months. Medical experts such as the Centers for Disease Control (CDC) and the National Institutes of Health, (NIH) mount pervasive PR campaigns urging all Americans to get vaccinated.  Indeed, there is considerable evidence to show that not getting vaccinated can lead to seriously bad health consequences.


But, have you ever wondered how the flu vaccine is manufactured? Is there a uniform manufacturing protocol? And why is it that some flu seasons are more severe than other years? Shouldn’t the vaccine equally protect regardless us — regardless of which flu strain is active during any particular winter? 

So, let’s take a look on how this critical vaccine is manufactured.



Flu Shots: The Manufacturing Process

The flu season begins each fall. For flu experts in the United States, however, it actually begins in February.


At that time, scientists and researchers from around the world gather for a meeting hosted by the World Health Organization (WHO). They spend days reviewing which strains of the flu virus have been making people sick and decide which strains the next season’s vaccine should cover.


But surprises and curve balls can happen. For example, this year, a new variety of the flu virus known as H3N2 had begun to spread rapidly in several countries. In the United States, it caused a second wave of illnesses late in the flu season. Therefore to get the right mix in the new vaccine, the release was postponed for a month.


This extra month gave experts more time to analyze the newly circulating virus. By March, they had updated their recommendation to include a suitable H3N2 strain for this season’s flu shot, which is now available.


More importantly, the delay showed how difficult it is to get the right mix for an effective vaccine.



flu shots

Flu Shots: Where Do You Start?

The challenge starts with the virus itself.

The flu is constantly changing — mutating as it replicates itself — in ways that allow its strains to get past our body’s immune system.

Therefore, in laboratories around the world, researchers must work quickly to analyze the flu virus and predict how it might change.


Surveillance and research starts when specimens from sick patients are sent to the lab for testing. Of those, about 7,000 end up at the laboratory run by microbiologist John Barnes, who leads the CDC’s influenza team.


He and his team perform year-round genetic sequencing to determine how flu viruses are behaving. They analyze which strains are infecting people and whether a specimen shows signs of resistance to the antiviral drugs that can treat the flu.


From there, about one-third of the CDC specimens will undergo more assessment. This is part of a labor-intensive process known as antigenic testing.



The Production Phase

In Swiftwater, Pennsylvania, the process begins with 1 million chicken eggs. They arrive every day during flu shot production season at the plant owned by Sanofi Pasteur. Sanofi is the world’s largest manufacturer of flu vaccines.


The fertilized chicken eggs are injected with the viruses that have been selected for that year’s vaccine. They then incubate for several days before the virus is extracted and inactivated for use in the flu shot.


The pressure also is on for U.S. manufacturers. They have about six months after that first February meeting to prepare, test and ship 100 million doses. These vaccines arrive at doctor’s offices, drug stores and clinics in August.


So, if you haven’t yet gotten the flu shot, the time to do it is now.

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