How COVID-19 Vaccine Developers Sprinted a Marathon

Why a “rushed” COVID-19 vaccine does not mean a riskier one

Chana Davis, PhD
9 min readDec 10, 2020


Vaccines against SARS-CoV-2, the virus responsible for COVID-19, have arrived!

The prospect of a COVID-19 vaccine before the end of 2020 seemed preposterous just a few months ago. Yet, here we are, getting ready to roll up our sleeves.

What are we to make of this “rushed” vaccine? Could it really be as safe as those that take years to develop?

The short answer is yes.

COVID-19 vaccines are required to clear all the same hurdles as past vaccines in order to gain regulatory approval. Their compressed timelines do not reflect less rigorous testing; they reflect the fact that COVID-19 vaccine development was an “all hands on deck” global priority.

To better understand why COVID-19 developers smashed the world record, let’s see what it takes to develop a vaccine, and how these steps were safely accelerated.

How are vaccines normally developed?

Photo by National Cancer Institute on Unsplash

Vaccine development always begins with a grueling search for the single best potential vaccine to test in humans. This pre-clinical (lab-based) stage often lasts for years, as developers simply can’t afford to place weak bets, given the steep costs of human trials.

Once a lead vaccine candidate is chosen, additional animal experiments are conducted to further evaluate safety. These experiments, which involve giving different vaccine doses to several species (e.g rodents and non-human primates, like monkeys) can take months, and are typically conducted prior to the first human trials.

The last phase of vaccine development is human testing, which is achieved through a series of carefully designed clinical trials. The three sequential phases of human trials are progressively larger and more expensive, reaching tens to hundreds of millions of dollars. At each phase, developers must gain approval from regulators, like the FDA, before proceeding.

Here is a quick summary of what happens at each phase:

  • Phase 1 trials test dozens of healthy adult…



Chana Davis, PhD

Scientist (PhD Genetics @Stanford) * Mother * Passionate about science-based healthy choices * Lifelong learner * Founder: Fueled by Science