How Vaccines Work

By: Alia Hoyt  | 

Vaccine Production Process

The process of creating, testing and producing a vaccine in mass quantities can take many years from start to finish because the industry is highly regulated. Before scientists even begin to formulate a vaccine, researchers have to study the particular virus or bacteria. Basically, they have to isolate it in a laboratory setting and figure out how it causes the disease. Then they develop the vaccine as either a live-attenuated or inactivated vaccine, depending on the type of virus or bacteria.

Once they have a good grip on that, researchers study the best ways to protect people from the disease using the vaccine they have developed. They figure out the best dosage amounts, whether or not one shot is good enough, or if more is necessary. They also estimate how long protection from the vaccine lasts to determine if booster shots will be necessary. Most of this early research is conducted in laboratories in an academic setting and is paid for by foundation or government grants.


Once the vaccine has been developed, the testing process is conducted over four phases and a period of many years. This testing is funded by pharmaceutical companies and can rack up hundreds of millions of dollars in bills.

The first studies usually test the vaccine on about a hundred healthy adults who are at low risk for complications. The researchers want to find out if the vaccine is safe and if it induces the immune response necessary to fight off disease. If this phase isn't successful, the vaccine is taken back to the drawing board or abandoned.

If Phase 1 is successful, the vaccine moves to the second phase of study, involving a few hundred people from the vaccine's intended group. For example, the chickenpox vaccine was probably tested on children at this phase because they are the target audience. The vaccine is tested on several hundred people to again ensure its safety. Researchers also want to verify that the vaccine causes the desired immune response consistently.

The third phase can take many years and studies anywhere from a thousand to tens of thousands of people in various lifestyles and geographic locations. Researchers want to make sure that the vaccine works on people of all types and in all environments. The FDA reviews all of the data and the study methodology. If everything is satisfactory, the FDA deems the vaccine safe, but then it must be approved by a board of vaccine experts who advise the CDC. The experts then distribute their recommendations about dosage, who should receive the vaccine, when they should receive it, etc.

Even after the vaccine has been distributed, it still requires many more years of study to make sure that no unforeseen side effects occur. The CDC monitors the vaccine and possible side effects very closely in four types of study:

  • Areas especially prone to the disease are closely monitored. All people who receive the vaccine are monitored closely. Results are reported to the CDC.
  • The CDC keeps an eye on any occurrence of the disease in the United States. If any strange pop-ups of the disease occur after the vaccine is introduced, it must find out if the vaccine and the pop-ups are related.
  • Health care professionals or consumers who believe that a serious side effect has occurred in a vaccine recipient can file a report via the Vaccine Adverse Events Reporting System. This data is continuously monitored to identify trends.
  • The Vaccine Safety Datalink Project provides data on millions of people regarding their vaccination histories and medical outcomes (whether or not they had side effects). This is carefully monitored by the National Center for Health Statistics' Research Data Center to make sure that no major side effects or health risks are occurring.

Who should get vaccinated – and when? For what? Read on for a thorough explanation.