Most vaccines have been in use for decades, with millions of people receiving them safely every year. As with all medicines, every vaccine must go through extensive and rigorous testing to ensure it is safe before it can be introduced in a country’s vaccine program.
Under normal circumstances, vaccine development is a long, complex process, often lasting 10-15 years and involving a combination of public and private involvement. The current system for developing, testing, and regulating vaccines has evolved during the 20th century as the groups involved in their development standardized their procedures and regulations.
Each vaccine under development must first undergo screenings and evaluations to determine which antigen should be used to invoke an immune response. This preclinical phase is done without testing on humans. An experimental vaccine is first tested in animals to evaluate its safety and potential to prevent disease.
If the vaccine triggers an immune response, it is then tested in human clinical trials in three phases.
Phase 1
The vaccine is given to a small number of volunteers to assess its safety, confirm it generates an immune response, and determine the right dosage. Generally, in this phase vaccines are tested in young, healthy adult volunteers.
Phase 2
The vaccine is then given to several hundred volunteers to further assess its safety and ability to generate an immune response. Participants in this phase have the same characteristics (such as age and sex) as the people for whom the vaccine is intended. There are usually multiple trials in this phase to evaluate various age groups and different formulations of the vaccine. A group that did not get the vaccine is usually included in phase as a comparator group to determine whether the changes in the vaccinated group are attributed to the vaccine, or have happened by chance.
Phase 3
The vaccine is next given to thousands of volunteers – and compared to a similar group of people who didn’t get the vaccine but received a comparator product – to determine if the vaccine is effective against the disease it is designed to protect against and to study its safety in a much larger group of people. Most of the time phase three trials are conducted across multiple countries and multiple sites within a country to assure the findings of the vaccine performance apply to many different populations.
During phase two and phase three trials, the volunteers and the scientists conducting the study are shielded from knowing which volunteers had received the vaccine being tested or the comparator product. This is called “blinding” and is necessary to ensure that neither the volunteers nor the scientists are influenced in their assessment of safety or effectiveness by knowing who got which product. After the trial is over and all the results are finalized, the volunteers and the trial scientists are informed who received the vaccine and who received the comparator.
Phase 4
In the Philippines, after a vaccine is authorized, it goes through a Phase 4 trial, where long-term effects are studied. Often referred to as Post Marketing Surveillance Trials, this phase aims to monitor a vaccine’s long-term effectiveness and impact on a patient's quality of life and detect rare adverse events that could only be attributed to the said vaccine. The Department of Science and Technology (DOST) earlier formed a Task Group on Vaccine Evaluation and Selection which oversees the evaluation of applications and Covid-19 vaccine clinical trials in the country.
To ensure the highest scientific and ethical standards are followed, the results obtained from the clinical trials are evaluated by the Philippine’s Food and Drug Administration (FDA) to assess the safety and effectiveness of each vaccine. The FDA gives the final approval and licensing of vaccines.
Author: Alona Estanilla Teo
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