In the United States, the review and approval of vaccines is the responsibility of the Food and Drug Administration (FDA). But the agency’s processing of emergency use authorizations for two antimalarial drugs and convalescent blood plasma for the treatment of COVID-19 has led to claims it has become politicized.
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The concern about the FDA’s impartiality is such that drug companies have drawn a line in the sand and publicly committed not to submit a vaccine “for approval or authorization for emergency use after demonstrating safety. and efficacy through a phase 3 clinical study ”.
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“Hell froze,” commenters noted.
But what is a phase 3 clinical study? And how do scientific tests give us reliable evidence that vaccines not only work, but are safe?
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Vaccine development can be thought of as the process of separating the parts of an infectious agent that make us sick from those that induce an immune response and protect us from future infection. As this separation can be achieved in multiple ways, vaccines are diverse.
The candidate vaccines for COVID-19 illustrate these various approaches. Some, like SinoPharm’s inactivated coronavirus vaccine, use a whole, killed coronavirus. Others, like the University of Oxford-AstraZeneca vaccine, modify a different virus (in this case, the chimpanzee adenovirus) to express the proteins of the coronavirus. Still others, like Moderna’s mRNA vaccine, use only small pieces of viral genetic material.
In Canada, vaccine surveillance is shared by Health Canada and the Public Health Agency of Canada. Scientific evaluation of vaccines includes animal testing, human clinical trials and post-approval surveillance. In many ways, the evaluation of vaccines is the same as that of drugs. However, because vaccines are given to healthy people, vaccine testing places even more emphasis on safety.
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The first step in evaluating a vaccine is animal testing. Animals are given different doses of vaccine to check for adverse events and an immune response.
With the virus responsible for COVID-19 being new, there was no animal model for the disease. Recent work has shown that ferrets, cats and some non-human primates are prone to infection and can pass it on to others. Animal testing provides information on safety (and possibly efficacy) before a vaccine is tested in humans.
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Human clinical trials
Human testing in clinical trials is divided into three phases. Ensuring the safety of a vaccine is the primary concern at all phases of clinical trials. The efficacy of the vaccine is assessed in different ways across the spectrum of trials. Early-phase trials look for the production of antibodies to the virus, while late-phase trials assess whether the vaccine is actually preventing people from getting sick.
Phase 1 trials are the first evaluations of a vaccine in humans. These trials recruit 10 to 100 healthy volunteers who receive different doses of the vaccine. Common adverse events associated with a vaccine include redness or pain at the injection site, muscle pain, headache, and fever. Blood is also drawn from the volunteers to assess the immune response to the vaccine, particularly the increase in antibodies and whether the antibody levels are similar to those of people who have had the disease.
Phase 2 vaccine trials are similar to Phase 1 trials in terms of focus on adverse events and immune response. Phase 2 trials, however, include hundreds of healthy volunteers who are more diverse to give a better indication of safety and immune response in people who may receive the vaccine in the future.
Since phase 1 and 2 trials involve a relatively small number of people, they only give us information about vaccine side effects which are very common (affecting more than 10% of people) and common (affecting more than 10% of people). 1% of people). The effectiveness of the vaccine is only evaluated indirectly by measuring antibody levels.
Only Phase 3 trials can provide crucial demonstration that a vaccine works and is safe. Phase 3 vaccine trials are large randomized controlled trials conducted in the community. In these trials, people are given the vaccine or a placebo. If fewer people who received the vaccine get sick compared to those who received a placebo, we have direct evidence that the vaccine prevents the disease.
A phase 3 trial can involve tens of thousands of volunteers who receive the vaccine, further providing reliable information on adverse events, including those that are infrequent (affecting less than 1% of people) or rare (affecting less than 1% of people). 0.1% of people).
A vaccine may be licensed for use after a successful Phase 3 trial.
Of the 321 COVID-19 vaccines in development, 27 are in phase 1 or 2 and six are being evaluated in phase 3 trials. In total, these trials aim to recruit 280,000 people from 34 country. No COVID-19 vaccine has been licensed in Canada or the United States.
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Once a vaccine is licensed, continued safety monitoring is essential. Reliable detection of very rare (affecting less than 0.01% of people) vaccine-related adverse events requires information on hundreds of thousands of people. The Canadian Immunization Adverse Events Surveillance System monitors the safety of marketed vaccines, publishes regular reports and identifies the need for further studies if a safety concern is identified.
Provided a COVID-19 vaccine successfully navigates human clinical trials and undergoes continued safety monitoring after licensing, we have good reason to believe the vaccine works and is safe.
Charles Weijer, Professor of Medicine, Epidemiology and Biostatistics, and Philosophy, Western University
This article is republished from The Conversation under a Creative Commons license. Read the original article.