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Why is Phase-3 of Vaccine Trial Complicated?

Written by Inshaa Siddiquee

The Covid-19 outbreak has proved to be one of the most challenging phases in our lives. However, many companies are racing towards developing a safe and effective vaccine to protect against Covid-19. Moreover, Phase 3 trials of investigational vaccines are underway.

How are vaccines developed?

New vaccines are tested in clinical trials to determine that they are both safe and effective. After the successful completion of clinical trials, they get licensed in US.

A lot of testing is done before a vaccine ever gets tested in humans. There is a long process of development in the laboratory.

The vaccine is firstly tested on various animals like mice, rabbits, hamsters and primates that have similar human physiology. After which their responses and reactions are studied. Because it is unclear whether these vaccines will work or not, a very structured set of clinical trials begins.

If the vaccine has proven itself it enters the Phase-1 studies.

What Happens in clinical trials?

The phase involves healthy volunteers who are informed about how and why these vaccines are being tested and also about a new potential harm. This process is called Informed Consent taken place before entering the trial.

The clinical trial comprises of 4 phases.

PHASE -1

PHASE -1 includes human pharmacology and safety. Testing takes place among a small group of people (roughly 30-60). It’s given in small doses and monitored to see if it is safe and well-tolerated.

However, a drug’s side effects might be subtle or restricted to a few people. In reference to this Phase-1 trial are not expected to identify all the side effects

PHASE -2

Phase-2 includes testing with a large group of people around 100-300 to determine the safe dosage range to get the desired response.

In reference to Covid-19, AstraZeneca vaccine had been put at halt at this stage. The pause was due to a harmful side effect reported by a volunteer in US who had been injected with the vaccine.

Nevertheless, promising vaccines that are safe and generate strong immune response move into phase-3 trials.

PHASE-3

Phase-3 is a larger version of phase-2 trial. It is held in multiple locations to capture the demographic variability in the population. It a complete randomized and double-blinded trial. Half of the volunteers are given the vaccine, whereas the other half are given placebo (salt water). As the process is double-blinded, neither the participants nor the study staffs are aware about who is getting which type of injection.

Furthermore, the study compares the rate of infection and placebo groups. It tells us whether the vaccine will be able to prevent the infection and if so, if it is effective enough in all of the volunteers or only a sub-group. Along with the safety data that is collected in all phases of vaccine studies, this efficacy data is used by the FDA to decide if the vaccine should be licensed.

In the case of Covid-19, there is an occurring trial of the US-MRNA vaccine.

The CEO of Moderna, Stéphan Bancel said, “The phase-3 for vaccine is a typical clinical trial, it’s a very large one of 30,000 people, 15,000 will receive the vaccine, whereas 15,000 will receive placebo and we will be able to see through data what is the safety of a vaccine and what is the efficacy of a vaccine”.

Across Europe, Brazil and other locations the Oxford vaccine is likely to be tested in the same way.

PHASE-4

A vaccine which clears all the phases is further sent for approval and license. After which the entire company is devoted to creating the vaccine in bulk, safely without it degrading or losing potency.

Post marketing studies delineate additional information, including the treatment’s risks, benefits, and optimal use. As such, they are ongoing during the drug’s lifetime of active medical use.

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