Paris (AFP)

The first vaccines against Covid-19 are arriving, and with them there are concerns among the general public about their possible adverse effects.

Update on what we know for the moment.

- What side effects?

Detailed data for two of the most advanced vaccines were released this week and both are considered safe.

On the one hand, data from the Pfizer / BioNTech vaccine, already authorized in several countries, appeared in the medical journal NEJM, after being unveiled by the US Medicines Agency (FDA).

The clinical trial carried out on some 40,000 volunteers shows that this vaccine causes classic side effects, often painful but without danger: 80% of the vaccinees had pain around the injection site, many felt fatigue, headaches or stiffness and some have had temporary swelling of the nodes.

More frequent and intense effects in the youngest.

Data from another vaccine, that of AstraZeneca and the British University of Oxford, appeared in another prestigious medical journal, The Lancet.

They show that this vaccine, administered to 23,000 volunteers in a clinical trial, "is safe," according to The Lancet.

These vaccines are based on two different techniques.

That of Pfizer / BioNTech uses a hitherto unprecedented technology known as "messenger RNA".

AstraZeneca / Oxford's vaccine is a "viral vector" vaccine: it takes another virus (a chimpanzee adenovirus) as a carrier.

- A high level?

In France, the statements of an infectious disease specialist, Prof. Eric Caumes, caused a stir.

He assured in several media that he was personally reluctant to receive the Pfizer / BioNTech vaccine, in particular because he had "never seen" a frequency of side effects "so high".

His statements have been coldly received by many other scientists.

To say that one prefers one vaccine to another amounts to saying that one "prefers chocolate ice cream rather than strawberry ice cream", objected virologist and vaccinologist Marie-Paule Kieny.

"We know that these vaccines are quite reactogenic (induce strong reactions, editor's note): their level of safety is quite satisfactory but on the other hand, they hurt the arm, cause a feeling of fatigue. This must be clear to citizens ", she said Friday during a parliamentary hearing.

She compared these effects to those of "pediatric vaccines", which can tire children: "it's unpleasant, maybe for a day, but these reactions are short lived and if combined with high levels of protection. , I think it must be tolerable ".

"It has nothing to do (...) with serious adverse effects", for his part underlined the immunologist Alain Fischer, charged by the French government to guide its vaccination strategy.

- How many serious side effects?

For Pfizer / BioNTech vaccine like AstraZeneca / Oxford, they are extremely rare at this stage.

Only one patient who was given the AstraZeneca / Oxford vaccine experienced a "possibly related serious side effect" from this injection, according to data published in The Lancet.

It was a case of transverse myelitis (a rare neurological impairment) which had motivated the temporary interruption of the trial in early September.

Two other cases of serious side effects were detected, without being attributable to the vaccine.

"These three participants are cured or in the process of being cured," according to those responsible for the trial.

In the case of the Pfizer / BioNTech vaccine, the only potentially worrisome side effect was the occurrence of four cases of Bell's palsy, an often temporary facial palsy.

But this frequency (4 cases among 18,000 people followed for two months) is not different from that generally observed for this paralysis, and we therefore do not know if it was caused by the vaccine.

As a precaution, however, the FDA recommended increased surveillance.

Finally, there were eight cases of appendicitis in the vaccinated, against four in the placebo group, the group to which the vaccine was not administered but a neutral product in order to be able to establish comparisons.

But the FDA thinks it is a statistical fluke, unrelated to the vaccine.

As with any drug, the hypothesis of a serious side effect for these vaccines cannot be ruled out.

But in medicine, a substance is evaluated by looking at the balance between its benefits and its risks.

"Given the benefits and effectiveness for people who are at severe risk of Covid, (...) it is quite acceptable to have a vaccine that is a little more reactogenic, if its adverse effects do not are not severe, "said Isabelle Parent, vaccine expert at the French Medicines Agency (ANSM) on Friday.

- What about allergies?

The day after the start of the vaccination campaign with the Pfizer / BioNTech vaccine in the United Kingdom on Tuesday, British authorities announced that two people had reacted badly to the injection.

They were both prone to severe allergies, to the point of always carrying adrenaline on them.

This has led health authorities to advise against this vaccine for people who have had in the past a "significant allergic reaction to vaccines, drugs or food (such as anaphylactic reactions or those who have been advised to take an adrenaline injector) ".

However, "this does not mean that the general population should be anxious about receiving this vaccine," said Professor Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, quoted by the British body Science Media Center (SMC).

Moreover, those responsible for the clinical trial which led to the authorization granted to Pfizer / BioNTech in several countries had anticipated this risk: they had excluded volunteers with a history of severe allergies to vaccines in general or to one of the components of the vaccine tested.

However, this does not seem to concern the millions of people allergic to, for example, eggs or peanuts.

"It is important to understand precisely what reactions" the vaccine caused in the two Britons "and to know their medical history, to better understand the risks", noted an expert from the University of Oxford, Professor Graham Ogg , cited by the SMC.

- What outstanding questions?

The main one concerns the hypothesis of undesirable effects which would occur later, since there is still little hindsight on these new vaccines.

Even if they are authorized urgently because of the pandemic, their data will therefore continue to be scrutinized by the global health authorities as vaccinations progress, in order to be able to react immediately if necessary.

This monitoring is called pharmacovigilance when it comes to drugs and vaccinovigilance when it comes to vaccines.

"This monitoring will help us identify any potential signs of side effects," said Dr Charlie Weller, head of vaccines at the Wellcome charitable foundation, quoted by the SMC.

In France, for example, a report on reported adverse reactions will be published every week, the ANSM said on Friday.

© 2020 AFP