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Secretary of Defense Memos

Mandatory Coronavirus Disease 2019 Vaccination of Department of Defense Service Members OSD007764-21 - PDF DOC


Pfizer Fact Sheet Patients and Caregiver BLA - PDF DOC

Development of New Vaccines

The general stages of the development cycle of a vaccine are:

  • Exploratory stage
  • Pre-clinical stage
  • Clinical development
  • Regulatory review and approval
  • Manufacturing
  • Quality control

Clinical development is a three-phase process. During Phase I, small groups of people receive the trial vaccine. In Phase II, the clinical study is expanded and vaccine is given to people who have characteristics (such as age and physical health) similar to those for whom the new vaccine is intended. In Phase III, the vaccine is given to thousands of people and tested for efficacy and safety.

Many vaccines undergo Phase IV formal, ongoing studies after the vaccine is approved and licensed.

For more information and to find out about new vaccines on the horizon, see the World Health Organization’s (WHO’s) Development of New Vaccines web page.

The development of the COVID-19 vaccine was unique in that stages were permitted to proceed simultaneously. But it is important to note that no steps in this process were skipped. Learn more about how the vaccine was developed and approved below.

Don’t vaccines usually take longer than this? Was this rushed?

The COVID-19 vaccines were not rushed but were prioritized. They are a product of international collaboration, prioritization and decades of vaccine research. They have been deemed safe and effective by the U.S. Food and Drug Administration and independent scientists across the country.

Although vaccines typically take many years to produce, that isn’t because researchers are holding to determine any long-term effects. Vaccines usually take longer due to finding funds, getting authorizations, ethics permissions and determining manufacturing and distribution. It is only until Phase IV, after FDA approval and widespread distribution, that close monitoring continues.

How was a COVID-19 vaccine developed so quickly?

Due to large investments from governments and philanthropic organizations across the world, the world’s top scientists and researchers were able to start working immediately and collaborating internationally.

In this case, approval for each stage of development was granted immediately or researchers were given enough resources to assist with animal ethics approval to volunteers for human trials. Typically, researchers spend months or years finding funding or searching for enough trial participants to have statistically significant data to analyze. Because the prevalence of COVID-19 is so high, it is easy for researchers to find thousands of volunteers, and it's easier to track if those volunteers get sick, therefore allowing vaccine trials to be conducted on a faster timeline.

Plus, international pharmaceutical companies increased the capacity for vaccines to be manufactured and distributed in large-scale quantities.

Were steps that are normally part of the approval process skipped?

No steps in the FDA approval process were skipped. Rather, stages were permitted to proceed simultaneously.

The COVID-19 vaccine trials have had record-breaking numbers of human participants: Over 43,000 participants for Pfizer alone, and 15 other vaccines in Phase 3 large scale trials. 

In comparison, the Ebola vaccine had approximately 15,000 participants in its Phase 3 trials. 

Below is a helpful comparison from the New York Times that shows how the vaccine development was prioritized compared to a typical timeline.


And the following from the CDC shows the steps involved in developing, approving and manufacturing a new vaccine:


Was the FDA under pressure to approve a vaccine?

Regardless of any objective external pressure from the president or public, the data speaks for itself. It has been meticulously studied by the scientific community to ensure large numbers of participants, lack of adverse events and high efficacy.

Two independent committees reviewed and recommended the approval of the vaccine before reaching the FDA, the Data and Safety Monitoring Board (DSMB) and the Vaccines and Related Biological Products Advisory Committee (VRBPAC). Additionally, the Western States Scientific Safety Review Workgroup, composed of nationally acclaimed immunization and public health scientists from California, Washington, Oregon and Nevada, have worked independently to assess the FDA’s review process.