Vaccine Cheat Sheet

How do vaccines get approved? A streamlined guide

A quick refresher as the race for a coronavirus vaccine heats up.

It might not feel like it, but Covid-19 vaccines are developing at lightning speed.

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There are dozens of vaccines in different stages of study.

Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases predicts we'll have at least one candidate by the end of the year (even if we don't roll it out to everyone then).

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Here's a how vaccines go from the lab to approval

... and where the historic coronavirus vaccine effort fits in.

Vaccine studies typically have four main phases, each with different goals.

Pre-clinical Studies

Studies on cells or animals


These are studies usually done in cells or animal models.

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The Goal:

To identify promising vaccine candidates.

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Phase I

The first stage of human testing

Phase I studies are usually conducted on a small group of about 20 to 100 healthy volunteers.

The goal:

Safety. Scientists look for signs of serious side effects and indicators that the vaccine is triggering an immune response, but safety is the focus.

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Phase II

An expanded phase of human testing

Phase II studies usually include "several hundred" volunteers according to the CDC.

The goal:

To search for side effects, and to measure the immune system's response to the vaccine, like the development of neutralizing antibodies, T-cells, or other signs that the immune system can recognize the pathogen.

Scientists also examine the effects of different dosages. The vaccine must be made in the building where the final product would be made (should it be approved), to help standardize manufacturing.

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Scientists may also be looking for "hints of efficacy" at this point, says Jonathan Kimmelman, director of the biomedical ethics unit at McGill University.

Remember: At this point, we still don't know if the vaccine actually works yet.

Phase III

The largest stage of human testing

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Phase III studies are usually done on thousands or even tens of thousands of people.

The Goal:

To find uncommon adverse events that wouldn't appear in smaller studies. Finally, it's also to see if the vaccine can actually prevent people from getting sick or infected.

This stage also includes thousands of people similar to those for whom the vaccine is intended, like people in a certain age group.

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"Phase 3 trials are large and long and allow us to detect uncommon adverse events, and prove that a vaccine protects against SARS-CoV-2."

- Jonathan Kimmelman (art by Michael Shillingburg)

In the case of a Covid-19 vaccine, there have to be at least 150 confirmed cases in a Phase III study before scientists can have an idea if the vaccine is working. More data provides a clearer picture.

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Once a vaccine gets through all four stages, the company can file a license application with the FDA for review.

The materials may also be reviewed by another, non-FDA advisory committee.

Overall, the process can take years. But there are ways it can speed up...

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It's possible a vaccine could be approved earlier during Phase III trials.

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If an independent Data Safety and Monitoring Board finds that Phase III trials have extremely positive results, that could trigger a "moral obligation" to end the trial early, Fauci told CNN.

That group can also stop the trial if interim results are concerning.

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And already the vaccine effort is moving at an unprecedented pace...

Kimmelman says the average timeline is about 4.4 years for a vaccine to get approved, if you include flu vaccines.

The Covid-19 vaccine race is moving much faster in part because scientists already had an understanding of coronaviruses, and some Phase I/II trials were combined or proceeded in parallel.

It's also because the massive public and private interests in making a vaccine for coronavirus are unique to the pandemic. >>

"It is virtually unprecedented for so many pharmaceutical firms to commit so much to the development of a vaccine," Kimmelman says.

Get caught up on key vaccine terms with this cheat sheet.

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