Vaccine Safety:
Understanding the vaccine development process

Ensuring the safety of each vaccine for New Zealand starts with testing. Data is collected from clinical trials around the world. The results of these trials are submitted to local health agencies who review the data. If the agencies conclude the vaccine is effective and its benefits outweigh any risks, it is approved for public use.

Couple lying on couch

How are vaccines made and tested?


Making a vaccine starts in a lab. Once lab tests show that it can work, it is sometimes tested in animals. If data indicates its benefits may outweigh its risk, it is then studied with human volunteers in clinical trials.



There are 3 phases of clinical trials an investigational vaccine must go through to ensure that its benefits are greater than its risks (side effects).

Erlenmeyer flask
Medical staff reviewing notes

Phase 1

The focus of this phase is to understand an investigational vaccine's safety. In this phase, scientists study how the size of a dose may relate to side effects.

Phase 1 clinical trials involve, on average, 20–100 healthy volunteers.
Medical doctor giving lecture

Phase 2

During this phase, scientists perform additional studies to gather more information on side effects. They also study how the size of a dose may relate to an investigational vaccine's ability to work correctly.

Phase 2 clinical trials have several hundred volunteers.
Medical doctor reviewing notes with patient

Phase 3

People who receive an investigational vaccine are compared with people who may receive a placebo or another vaccine. This is done so scientists can learn more about how well the investigational vaccine works and see if there are any side effects. In the case of the global COVID-19 health crisis, participants who received a placebo were also able to receive the investigational vaccine if they chose to participate in the crossover part of the trial.

Phase 3 clinical trials can have from a few hundred to thousands of volunteers.

and Distribution

After the local health agency authorises or approves the investigational vaccine based on the trial results, it can be made available for public use.

Novavax shipping boxes


A local health agency will continue to monitor a vaccine's safety and watch for possible side effects even after it is approved. High safety standards and testing help to ensure that vaccines in New Zealand meet quality standards.

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Possible Side Effects
from Vaccines

Side effects can differ based on each individual. The most common side effects from vaccines are usually mild and go away quickly on their own.

Some of the common side effects include:

  • Pain, swelling or redness where the shot was given
  • Mild fever
  • Chills
  • Feeling tired
  • Headache
  • Muscle and joint aches
Person being protected by virus

Side effects from vaccines are usually a sign that your body is starting to build immunity. They typically go away a few days after receiving a vaccine.