Everyone wants an effective and safe treatment
or vaccine for COVID-19
as soon as possible.
To reach that point,
therapies and vaccines need to
go through a series of clinical trials,
says Mindy Aisen,
clinical professor of Neurology
at the University of Southern California.
The process can take several months
or in some cases, many years.
Pre–clinical trials are conducted on
cells or non-human subjects
such as rats or primates.
The purpose is to see whether
the intervention has any potential,
and whether it is safe for testing on humans.
Phase-1 trials involve
around 20-100 healthy volunteers
or infected people.
Around 70% of drugs
pass phase 1 trials
and these can be considered safe,
but not necessarily effective.
Phase-2 studies hundreds of subjects, 
and are focused on applying ‘successful’ doses
based on phase-1 results.
About 33% of drugs that make it to
phase 2 trials proceed to Phase-3.
At this point,
scientists focus on the efficacy and side effects
testing groups of 300-3000 participants.
If researchers determine the treatment is medically important,
it moves ahead.
Only 25-30% of drugs that undergo phase 3 trials
receive FDA approval.
Phase 4 occurs after FDA approval.
It provides information about the real world
use of medications
outside controlled environments
One example is testing whether
a vaccine approved for adults
is also safe and useful for children.
