COVID-19 vaccines: Vaccine Testing Process

PRECLINICAL TESTING: Scientists test a new vaccine on cells and then give it to animals such as mice or monkeys to see if it produces an immune response.

PHASE 1 SAFETY TRIALS: Scientists give the vaccine to a small number of people to test safety and dosage, as well as to confirm that it stimulates the immune system.

PHASE 2 EXPANDED TRIALS: Scientists give the vaccine to hundreds of people split into groups, such as children and the elderly, to see if the vaccine acts differently in them. These trials further test the vaccine’s safety.

PHASE 3 EFFICACY TRIALS: Scientists give the vaccine to thousands of people and wait to see how many become infected, compared with volunteers who received a placebo. These trials can determine if the vaccine protects against the coronavirus, measuring what’s known as the efficacy rate. Phase 3 trials are also large enough to reveal evidence of relatively rare side effects.

EARLY OR LIMITED APPROVAL: Many countries have procedures for providing emergency authorizations for vaccines, based on preliminary evidence that they are safe and effective. In addition, some countries such as China and Russia began administering vaccines before detailed Phase 3 trial data was made public. Experts have warned of serious risks from jumping ahead of these results.

APPROVAL: Regulators review the complete trial results and plans for a vaccine’s manufacturing, and decide whether to give it full approval.

COMBINED PHASES: One way to accelerate vaccine development is to combine phases. Some vaccines are now in Phase 1/2 trials, for example, which this tracker would count as both Phase 1 and Phase 2.

PAUSED or ABANDONED: If investigators observe worrying symptoms in volunteers, they can pause the trial. After an investigation, the trial may resume or be abandoned. Trials may also be abandoned if they indicate a vaccine isn’t effective against Covid-19.