When being developed, each vaccine has to go through a process of screenings and evaluations. This helps to find out which antigen needs to be used to create the correct immune response when administered. In this preclinical phase, no testing takes place on humans - usually, it is initially tested with animals so that the safety and the extent that it is able to prevent disease can be assessed. Should the vaccination be successful with triggering the correct immune response, then it goes on to be tested with human clinical trials. These trials take place in three phases.
First Phase: A small number of volunteers receive the vaccine. This takes place to do an initial test of its safety, to make sure that an immune response is elicited following its administration, and to establish the correct dosages. Usually, this group of volunteers are made up of young, healthy adults.
Second Phase: The volunteer numbers in this phase are increased to several hundred, and is usually made up of individuals with similar characteristics as the population that is later going to be receiving the vaccine - such as being of a similar age or sex. This phase further establishes the vaccine’s safety and ability to generate an immune response, according to the World Health Organisation. Usually, a group of people who did not receive the tester vaccine is included in this phase for comparison. This helps to assess if the changes in the group that were vaccinated were by chance or can be attributed to the vaccine.
Third Phase: Following the success of the first two phases, the vaccine is then received by thousands of volunteers. These are a group of people who are compared to a similar group of people who do not receive the vaccine, but will have recited a comparator product. This establishes if the vaccine is effective against the disease that it is designed to protect and to research its safety in a group that is far bigger. Oftentimes, this third phase trial takes place across many countries, at multiple sites within each of those countries to ensure that the findings of the testing can apply to many different populations.
In the trials in both the second and third phases, both the volunteers and scientists who are involved in the study and conducting the research are not informed of which volunteers receive the actual vaccine that is being tested - or if they are given the comparator product. This method of testing is known as ‘blinding’ - and is essential so that neither the scientists or volunteers are under the influence of such knowledge during the test. This influence can happen, should they be told, and can impact both the safety and effectiveness of the study. Following the trial, the results are finalised, and then only do the volunteers and scientists find out who received the vaccine and who received the comparator, as stated by the World Health Organisation.
Following these three phases, ongoing monitoring of the vaccine takes place. Systems are in place to monitor both the safety and effectiveness of all vaccines - which helps scientists to track themes even after a longer time period. The information gathered from the tracking is made use of to organize the impact that the vaccine can have, as well as the tracking of the safety of the vaccine throughout its use. This is continually monitored throughout the use of a vaccine.