Covid-19: what are the differences between Moderna and Pfizer vaccines?

As part of the recall campaign, Moderna vaccine (21 million doses) is now more available than Pfizer (9 million). Vaccination centers must therefore sell the first in priority, but sometimes they face rejection from patients, which they have a priori in Moderna. However, according to several studies, Moderna is as effective as Pfizer, if not better. What is it really?

Since the start of the vaccine booster campaign for everyone over 18 years of age, the Pfizer vaccine is harder to find than Moderna. And for good reason: France has more stocks of the latter. A phenomenon that worries some French, reluctant to combine different vaccines or to receive Moderna instead of Pfizer, due to the risk of myocarditis indicated.

However, Olivier Véran stated in Franceinfo that these two vaccines could be administered interchangeably. “I tell the French who have taken two doses of Pfizer and are worried about having Moderna: no problem. And in the same way, to the French who have had Moderna twice and to whom we are going to offer Pfizer: don’t worry, it’s the same. “Is this really the case?

The same messenger RNA technology

These two vaccines use the same technology: messenger RNA. While both can be injected in the third dose, the Moderna vaccine is not given to people under 30 because of the risk of myocarditis, which is higher in young people with this vaccine than with Pfizer, as the Epiphare study revealed. However, it is rare and has a favorable evolution.

If this risk is greater with Moderna, it is due to “the amount of vaccine (…) which is a little more important,” Jean-Daniel Lelièvre, head of the department of immunology at the Henri-Mondor hospital in Créteil (Val- de-Marne). However, this higher dose would have an advantage: “It will increase the initial response. Therefore, in primary vaccination, Moderna has better protection against Delta,” said the specialist. This is also what the High Health Authority underlined in an opinion of November 8.

3rd dose: good immune response with all vaccines

So Moderna would be more effective than Pfizer for the first two doses, but what about booster shots? This is one of the questions the British researchers wanted to answer as part of a study published in The Lancet on December 2. This work aimed to assess the immune response after a third dose of seven different anti-Covid-19 vaccines, including Pfizer and Moderna. The research was carried out in 2,878 adults over the age of 30 who had initially received two doses of Pfizer or AstraZeneca.

Results? All tested vaccines improved immune responses after two doses of AstraZeneca, but only Pfizer, Moderna, AstraZeneca, Novavax, Janssen, and Curevac had the same effect after two doses of Pfizer. “It is really encouraging that a wide range of vaccines, using different technologies, have advantages as a third dose, either with AstraZeneca or Pfizer,” commented Professor Saul Faust, lead author of the study.

Anti-Covid-19 vaccine: heterogeneous booster, even more effective?

What about the side effects identified since the start of the vaccine booster campaign? In its latest surveillance update published on December 3 and covering the period from November 12 to 25, the National Agency for the Safety of Medicines and Health Products (ANSM) indicated that no specific signal has been identified after the administration of a heterologous scheme, that is, a vaccination schedule carried out with different vaccines. If side effects have been observed, “they are comparable to those already observed from the start of vaccination.”

For its part, the European Medicines Agency stressed, on Tuesday, December 7, the interest in combining different vaccines. “The data available to date with different types of licensed vaccines indicate that a heterologous boost appears as good or better in terms of immune responses than a homologous boost.”

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