Coronavirus: five questions posed by Pfizer's announcement on the effectiveness of its vaccine

The announcement Sunday at the end of the day of a vaccine candidate '90% effective' is a shock. This announcement also raises many questions. Here are five, to help you see more clearly.

Duration of protection, effectiveness in subjects at risk, the logistical challenge of storage at very low temperature ... Many questions remain unanswered after the announcement by Pfizer and BioNTech that their vaccine candidate is "90% effective" against Covid-19.

What does "90% effective" mean?

To assert this, the American pharmaceutical giant Pfizer and its German partner BioNTech are based on interim results from phase 3 of their clinical trial, the last before an application for approval.

According to them, the cases of coronavirus infection are reduced by “more than 90%” in the trial participants who received the vaccine, compared to those who received a placebo. A finding made when 94 participants caught Covid-19 at this stage of the trial, out of a total of 43,500 volunteers.

However, the two pharmaceutical companies do not give details: of the infected patients, it is not known how many belonged to the group that received the vaccine and the one that received the placebo.

More broadly, the two companies made their announcement through a press release - resulting in a sharp rise in world stock markets - but there has not yet been a detailed publication in a scientific journal. "These results are extremely interesting, but we must wait to see the data, which are not yet available", summarizes for AFP the French virologist Marie-Paule Kieny, researcher at Inserm and former head of the WHO.

Finally, in addition to the question of effectiveness, the two companies must continue to collect data on the safety of the vaccine and its possible side effects, even if "no serious problems" have according to them been observed at this stage.

What duration of protection?

The elements unveiled Monday by Pfizer and BioNTech do not allow to say. In fact, the 90% efficacy was measured seven days after the injection of the second and last dose of the vaccine, ie 28 days after the first (three weeks separating the two injections). This is a "downside," Bruno Pitard, CNRS research director, told AFP.

These preliminary results seem to show that "vaccinated individuals are really armed a week after" the second injection, when the immune response "is maximum", but that "does not tell us what will happen after", continues this expert. French.

With a view to possible authorization by the United States Drug Agency (FDA), the two companies have indicated that they will also publish results measured 14 days after the second injection.

For Bruno Pitard, one of the challenges is to know how the effectiveness of the vaccine changes over time: "After three weeks, then a month, then two, then three then four, we will see if the protection is still the same" .

What does this vaccine protect against?

Does it outright prevent infection with the SARS-CoV-2 coronavirus or does it only reduce the symptoms of the disease by avoiding severe forms? Does having received this vaccine mean that you can no longer transmit Covid-19? There again, no answer at this stage, for lack of publication of scientific data.

"If the vaccine protects against the infection itself, and therefore decreases the risk of transmission from asymptomatic people, this could allow us in the future to reduce control measures" of the epidemic, says a British expert, Dr. Penny Ward, cited by Science Media Center.

"But if it protects against the risk of disease, and not against the infection itself, then the control measures will have to remain in place until a sufficient number of people have been vaccinated," continues Dr Ward, specialist with King's College London and the British Faculty of Pharmaceutical Medicine.

Is it effective in people at risk?

Ten months after the appearance of this new disease, we know that certain categories of the population are more at risk than others of developing serious forms. Among these risk factors, old age, obesity, diabetes, hypertension or the presence of other diseases (cardiovascular in particular).

However, the fragmented data made public by Pfizer and BioNTech do not allow us to know whether their vaccine is effective in these people at risk.

"In scientific publications, we see all this stratification of individuals, according to age, the presence of comorbidities (other ailments in addition to the disease studied, note), ethnic origin, etc. There, we do not has not all that ", notes Bruno Pitard.

The cold, a brake?

The vaccine developed by Pfizer and BioNTech is based on very innovative technology, which has never been used in real life before. It involves injecting the body with strands of genetic instructions called messenger RNA, which tell our cells what to make to fight the coronavirus.

It is on this technique that the vaccine project developed by another company, the American firm Moderna, is also based.

However, these messenger RNA vaccines must be stored at very low temperature (-70 degrees Celsius for that of Pfizer / BioNTech), which can be a major logistical obstacle for their distribution around the world.

"It's a problem", emphasizes Bruno Pitard. "When you go to get your flu shot from your neighborhood pharmacist, he'll take it from his back room fridge. But he doesn't have a -80 degree fridge."

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