Why we must continue to trust vaccines


Why we must continue to trust vaccines : How do we know that a vaccine is safe and works?

Why we must continue to trust vaccines : Before human clinical trials can begin, the vaccine is tested in the laboratory to be non-toxic and has no side effects in cell cultures and animal models. Typically, doses higher than those that would be used in humans are applied and possible adverse effects are checked.

It is also studied in animal models if the vaccine induces the production of antibodies – if it activates the defenses – and if it is capable of protecting against an experimental infection. Since humans are very different from a laboratory mouse, sometimes a vaccine that works very well in animals does not work in humans. If the results of this preclinical development are satisfactory, permission is requested from the health authorities to begin the clinical phases of experimentation with human beings.

Human clinical trials are in turn divided into several phases.

Why we must continue to trust vaccines : Phase I consists of evaluating the safety of the vaccine (which is not toxic or has serious side effects in people) and immunogenicity (its ability to induce an immune response, antibody production, and cellular immunity). It is usually done with a few healthy volunteers (between twenty and one hundred).

If the results are satisfactory, you can proceed to phase II, in which the safety and immunogenicity of the vaccine is re-evaluated, but with a greater number of volunteers (between one hundred and two hundred). It also takes into account how it can affect the age and sex of the person, and several doses are usually tried. But we still don’t really know if the vaccine works. We can already know if it has any toxic or secondary effect and even if it stimulates the defenses, but we do not know if this stimulation is really enough to protect us against infection.

Why we must continue to trust vaccines : If the results continue to be satisfactory, it is authorized to advance to phase III, in which the efficacy of the vaccine is already tested. In this phase III, a good group of volunteers are already involved (in some cases several thousand) and the efficacy of the vaccine is tested and compared with controls of unvaccinated people who have been inoculated with a placebo. Apart from verifying its effectiveness, it is also determined if there are any previously undetected toxicity or side effect. To avoid bias, trials are conducted without knowing until the end who has been vaccinated and who has not (the control group): this is what are called ‘double blind’ trials.

Obviously, volunteers are not deliberately infected at this stage, but are allowed to continue with their lives and some of them are expected to become infected naturally. When this happens, it is checked who was vaccinated and who was not, and from there it is estimated how effective the vaccine is.

This is, for example, what Pfizer / BioNTech and Moderna have announced (90 and 95 volunteers were infected with covid-19, respectively, of which the majority were unvaccinated). Throughout the process, the results are evaluated by external agents, who give their approval and authorization to move from one phase to the next. Any adverse outcome on the safety or efficacy of the vaccine leads to discontinuation of the trials. In addition, the results are published before their commercialization so that they can be reviewed by the scientific community.

If the vaccine has finally passed all the “filters” and is authorized to be marketed, we must not forget that a fourth phase of epidemiological monitoring begins.

Why we must continue to trust vaccines : No drug is 100% safe, because none of us are 100% identical. For example, a vaccine that causes some type of serious side effect with a very low frequency of one per million vaccinated, It will only be detected in this surveillance phase. It is, therefore, a matter of detecting possible side effects that may have previously gone unnoticed.

These studies that are carried out after the vaccine has been approved also aim to evaluate its effectiveness: how it works in the “real world”, to see if it works to control the disease. Therefore, a vaccine, in addition to being safe, must be efficient and effective.

The term efficacy refers to the protection provided by the vaccine in clinical trials under optimal conditions (storage and distribution) in a group of generally healthy volunteers and under close surveillance. This is what is studied in phase III. But efficacy is not the same as effectiveness, which refers to the protection generated by the vaccine in real conditions, when it has already been approved and is distributed in the population, in phase IV. It could happen that a vaccine is effective in clinical trials, but then when it is used in real conditions, its effectiveness in controlling the disease is less.

With all this it is achieved, as I have said, that vaccines are the safest drugs that exist. This also implies that it should not be surprising that a vaccine that is already on the market may be withdrawn if a problem is detected during this phase IV. This would show that the surveillance system works.

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