Covid-19 vaccines: how are adverse effects determined?

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How are the adverse effects of Covid-19 vaccines determined? Should we fear new ones with the most recent serums? Answers with Jean-Louis Montastruc, professor of medical pharmacology at the Toulouse University Hospital.

More than a year and a half after the first vaccines against Covid-19 were put on the market, what do we know about their side effects? How are they detected and to what extent do they differ according to the types of serums? In order to see more clearly, La Dépêche takes stock with Jean-Louis Montastruc, professor of medical pharmacology at the Toulouse University Hospital.

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“To determine the side effects of vaccines against Covid-19, two methods are used. The first is that of spontaneous notification”, explains the pharmacologist.

“It is based on the declarations, by the doctors or by the patients, of the undesirable effects felt following the vaccination. Once collected, these elements are transmitted to the networks of the regional centers of pharmacovigilance”. France lists 31 of these centres, with each former region having at least one.

“First Alert”

Subsequently, “we determine the imputability, that is to say the cause and effect relationship” between the symptoms and the vaccine. “‘Are there other causes to consider? Is the time to onset compatible? Are the clinical signs in agreement with the effect felt? This method in fact makes it possible to draw up a first alert”, continues the scientist.

Then comes the second phase of detection. “This consists of verifying, on large databases, the association between the vaccine and the effects detected. Here we use pharmacoepidemiological methods”, specifies Jean-Louis Montastruc.

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“It is during this phase that we see that many events reported to health authorities would have occurred spontaneously without a vaccine. For example, when a patient reports depression following an injection, we know that few arguments support this association.

To date, the most common side effect is flu syndrome. “We have chills, a little fever, fatigue for a few hours or possibly days… These symptoms occur very frequently, and we know today that they are absolutely not serious”, explains the pharmacologist. “We also find them as much as with the flu vaccine, for example”.

No new side effects with the latest vaccines

And what about the most recent vaccines? For example, can Novavax serum, which uses not messenger RNA technology, but so-called “recombinant protein” technology, cause new undesirable symptoms? “Some effects differ slightly, but they are generally the same as with the other vaccines”, observes Jean-Louis Montastruc.

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And on the side of updated vaccines to fight Omicron variants and subvariants, “it’s the same thing,” he explains. “A recent study from pharmaco-vigilance centers shows that there are no new signals with these established vaccines against Omicron. They are exactly the same adverse effect profiles”.

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