• While the general population is called upon to receive its booster dose, some wonder about the possible differences between the two messenger RNA vaccines available.

  • The sera developed by Pfizer and Moderna are both based on the same technology, and have comparable rates of effectiveness.

  • There are, however, small differences between the two vaccines, which do not target exactly the same populations.

"Pfizer or Moderna"? "Moderna or Pfizer"? By typing the name of one of the two vaccines into a search engine, the name of the other appears in the process, a sign of the questions of the French at the time of the booster dose, who no longer know which serum to use. vow. "It can be Moderna or Pfizer, indiscriminately", "it's the same", assured the Minister of Health, Olivier Véran, Friday on franceinfo.

Less than ten days before school holidays, the runaway wave of the fifth wave of coronavirus casts a gloomy shadow over the holidays.

The head of government, Jean Castex, called on the French to limit their social interactions before Christmas, but the government is mainly focusing on vaccination.

And if he is preparing its imminent opening to children, for the time being, he especially wants to put the package on the deployment of the booster dose in the general population.

But before being injected into the arms, into the hearts, the two vaccines do not inspire the same feelings.

For those over 18 (who manage to get an appointment), there is a rush towards Pfizer, while Moderna is rather shunned.

So, between the two messenger RNA (mRNA) sera, is it kif-kif bourricot?

Moderna advantage for efficiency

In the context of an epidemic outbreak caused by the Delta variant, and while the Omicron variant has already been detected in at least 38 countries, some wonder if, between the two anti-Covid mRNA vaccines, one is more protective than the other. "These two vaccines are" twin brothers ", they are based on the same technology and have a comparable effectiveness, close to 95%," says the Ministry of Health.

But according to the scientific literature, the advantage would go to Moderna on this point.

“Several studies conducted under real conditions of use tend to show a slightly higher vaccine efficacy for Spikevax [Moderna] compared to Comirnaty [Pfizer-BioNTech], whose efficacy is already very good, confirming the interest of Spikevax, in particularly in people at risk of a severe form of Covid-19, ”indicates the High Authority for Health (HAS) in an opinion published on November 8.

An advantage that Moderna would also retain over time, thanks to an efficiency that would drop less quickly over the months than its competitors.

A study published in the journal


November 4 followed for six months a sample of 780,000 veterans of the American army.

The observed results confirm that the vaccines from Pfizer, Janssen and Moderna lose efficacy over time, but in different proportions.

Six months after the second dose (or the dose for Janssen), the Janssen, Pfizer and Moderna vaccines showed protection against infection of 13.1%, 43.3% and 58%, respectively.

And at the same time offered a level of protection against severe forms and death of 73% for Janssen, 84.3% for Pfizer and 81.5% for Moderna.

Pfizer Advantage for French Membership

Despite these figures, Moderna arouses mistrust and it is Pfizer which wins the adhesion of the French. On booking platforms, the deadlines are not the same depending on whether you check Moderna or Pfizer as a preference for your booster dose. If for the first, it is possible to find a time slot in Paris during the week, for the second, you have to be patient, with first availability displayed in 2022, sometimes not before April or May. In question, stocks: while 85% of the available Pfizer doses have already been injected, only 41% of the Moderna doses delivered to France have been administered.

Why such a gap? At the origin of the mistrust, the risks of myocarditis, an inflammation of the heart muscle, higher with Moderna's vaccine. EPI-PHARE, the scientific interest group led by the National Medicines Safety Agency (ANSM) and the Cnam, has conducted a "new pharmacoepidemiology study to characterize the risk of myocarditis and pericarditis with mRNA vaccines in subjects aged 12 to 50 in France ”. And if this study, published in early October, "confirms the existence of an uncommon risk of myocarditis with an mRNA vaccine, particularly in young people aged 12 to 29, this risk is higher with the Spikevax vaccine" from Moderna, indicates the ANSM.

As such, the HAS recommends, in its opinion of November 8, "for the population under the age of 30 and when it is available, the use of the Comirnaty [Pfizer] vaccine, whether it is first vaccination or booster ”.

Earlier, on October 6, the HAS launched the campaign for the third dose only with Pfizer, awaiting the opinion of the European Medicines Agency (EMA) on the use of Moderna as a booster dose.

A different dosage

Another difference between the two serums: their dosage.

The Moderna is more dosed than its almost twin Pfizer.

If a dose of the first must be diluted with 0.9% sodium chloride before injection and contains 100 micrograms of antigens, a dose of the second contains only 30 micrograms and is injected pure.

And when it comes to vaccinating the youngest, the differences tip the scales in favor of Pfizer, the first vaccine approved by the EMA and by the HAS for 12-17 year olds in France. It is even the only vaccine authorized a few days ago for the vaccination of children aged 5 to 11, which could start in mid-December for 360,000 children "at risk" of developing serious forms of the virus. And "if possible at the end of the year" for the others, "on a voluntary basis", announced Jean Castex, while the executive is still awaiting the "green lights" of the HAS and the National Consultative Committee of ethics (CCNE).

For this young audience, the dosage will not be the same.

It will be "three times lower than the dosage used in adults", with only "10 micrograms of antigens", underlined on franceinfo Professor Daniel Floret, pediatrician and vice-president of the technical commission of vaccinations of the HAS.

The government has already organized the logistics, since "the first delivery of Pfizer vaccines with a dilution suitable for children will be made on December 13," said Olivier Véran.

To date, more than 12 million French people have already had their booster dose, and Olivier Véran hopes that "on December 30, more than 15 million French people will have had it".


Coronavirus: Vaccination, school health protocol, teleworking… Announcements from Jean Castex's press conference


Vaccination in Île-de-France: Faced with the 5th wave, it is easier to have your 3rd dose

  • Pfizer-BioNTech

  • Moderna

  • Anti-covid vaccine

  • Health

  • Covid 19

  • Coronavirus

  • Vaccination

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