Keys to understanding clinical trials of vaccines, drugs for Covid-19

By Noemí G. Gómez

Madrid, Mar 21 (efe-epa).- The United States and China have begun human trials for a prospective coronavirus vaccine and dozens of countries have begun tests of existing drugs, but how are clinical trials going? And what is their time frame?

Vicente Larraga, from the Margarita Salas Biological Research Center (Spanish National Research Council) and Eduardo Oliver an expert in pharmacology from the National Center for Cardiovascular Research, explained where research and testing stand at present to Efe.

Question: What is a clinical trial?

Answer: It is an experimental evaluation of a drug or vaccine in humans to verify its safety and efficacy. The process is reached after successful animal testing.

Q: How many phases does a clinical trial have?

A: Clinical trials have three phases plus a fourth review applicable only when the drug or vaccine has already been approved by regulatory agencies and is on the market. Each of the stages of a trial is designed to answer a set of questions.

Q: What does the first phase consist of?

A: Safety is tested and it is the first time that the substance is administered to humans. This phase is carried out with less than 100 healthy volunteers and its main objective is to establish whether it is safe and does not cause harm to people. It also serves to determine the best way to administer it and what an appropriate dose would be.

Q: What is examined in the second phase?

A: Once a candidate for a vaccine or medication is proven to be safe, its effectiveness must be determined. A greater number of people participate in this phase although the number does not usually exceed 500. With clinical trials for drugs, participants are people with diseases. In the case of preventive vaccines only healthy people are tested.

Q: What happens in phase three?

A: Thousands of people are involved, from multiple centres and countries. Medications are compared, if applicable, with other treatments already in use. With vaccines, this is the phase to check whether immunization really protects the population against exposure to the pathogen. If the results are positive, drug regulatory agencies can grant authorization and sale of the drug or vaccine.

Q: How long does a clinical trial last?

A: The average duration with all three phases can be six to seven years, although this varies depending on the disease and treatment. With the coronavirus, there are hundreds of groups worldwide investigating and it is expected that time frames will shorten.

Drugs will be narrowed down because medicines already on the market used for other diseases are being examined which allows for trials to start directly in phase two or three (as is the case of Remdesivir, used to treat HIV and Ebola, or the antimalarial hydroxychloroquine often used to treat rheumatoid conditions).

Q: What are the differences between a vaccine and a drug trial?

A: The phases are the same but from the first stage there are some distinctions. In phase one of a drug trial, the effect of a drug cannot be tested, only its safety. But with vaccines, it is a little different.

Vaccines are designed for healthy people, they are preventive, so you can start to see the degree of immunization if after inoculation people develop antibodies against the virus. Therefore, the first phase of a clinical trial with vaccines offers more information than with a drug.

However, vaccines also need phases two and three to learn the degree of protection. In other words, how many participants have been infected when comparing those who have been given the vaccine and those who haven’t.

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