Q: The figures show that the AstraZeneca vaccine is less effective than messenger RNA vaccines. Are there any plans for people vaccinated with AstraZeneca to be able to receive a third dose to increase their protection?
Élise Poudrette
A: Before talking about a possible third dose, let’s take a look at the data about vaccine effectiveness. Is it correct to say that the AstraZeneca (AZ) vaccine is less effective than a messenger RNA vaccine? It all depends on what figures we are talking about, underlines Alain Lamarre, professor at the Jeanne and Jean-Louis Lévesque Research Chair in immunovirology at the National Institute for Scientific Research. “If we take the data on infections and diagnoses combined, it’s true,” he emphasizes. But it depends on when the test is administered. If it is immediately after the vaccine, the two types of vaccine are equally effective. Second, the efficacy of AZ declines faster than that of the messenger RNA vaccine. Faced with the Delta variant infection – which represents the vast majority of COVID-19 cases at present -, it is estimated that the protection rate of the AZ vaccine is around 50-60% while vaccines with Messenger RNA 80-90% protection. But after six months, the effectiveness of the two types of vaccine was again the same against infections. As for the interval between the two doses, extending the interval to 10 or 12 weeks rather than 8 weeks has little impact. ”
On the other hand, if we are talking about the prevention of hospitalizations and deaths, the two types of vaccine are just as effective.
Now let’s talk about the possible third dose. For the moment, still according to Alain Lamarre, only the immunocompromised are entitled to it.
“For those who have received the AZ vaccine, that is to say people aged roughly between 45 and 65 years old, the question of the third dose will arise around the month of February. And at that time, they probably risk being offered a dose of the Pfizer vaccine, ”notes Alain Lamarre.
So let’s recap: if you have received the Pfizer or Moderna vaccine you are approximately 80-90% protected from a Delta variant infection, but if you have received two doses of the AZ vaccine you are 50-60% protected. We therefore recommend that you remain vigilant, avoid direct contact with unvaccinated people, wear a mask and observe the health regulations in force.