Posted at 5:00 a.m.
“If I received my third dose more than three months ago, should I receive a booster dose this winter? »
This is the case for some readers, like Mario St-Pierre. “My first dose was the AstraZeneca vaccine. The second, Pfizer. Since I had to travel, I got a second dose of the Pfizer vaccine more than three months ago. Am I considered to have three doses? »
It is called the “third dose”, since it will indeed be the third for the vast majority of vaccinees. But in fact, its official name is “booster dose”. And, yes, Mr. St-Pierre, like all other people whose last dose dates back more than three months, is eligible for a booster dose, confirms the Ministry of Health and Social Services (MSSS).
In its latest opinion, the Committee on Immunization of Quebec allows these people to receive a “fourth dose”, provided that they know that “there are still uncertainties about the benefits and risks associated with the administration of ‘such a booster dose’.
“Can we receive the Moderna vaccine in the third dose if we received AstraZeneca in the first dose and Pfizer in the second? Will this be a problem for future trips abroad? »
On many occasions in recent weeks, Quebec and Canadian public health authorities have asked those vaccinated not to turn their noses up at the manufacturer of the vaccine that would be offered to them for the booster dose. More often than not, people who had received the Pfizer vaccine refused the Moderna vaccine offered to them.
The two mRNA vaccines are similar, experts say. Statistical evaluations, however, showed a slightly higher prevalence of the (very rare) risk of myocarditis or pericarditis with that of Moderna in those under 30 – which is why Pfizer’s vaccine is favored in 18-29 year olds.
Around the world, health authorities also recognize vaccines from Pfizer and Moderna. In the United States, the interchangeability of these two booster dose vaccines has been permitted since last fall. Note that the vaccination schedule that combines doses of AstraZeneca and mRNA vaccines is also recognized in the United States.
“How long do you have to wait after an infection to receive a dose of vaccine? »
The answer depends on who you ask the question… On January 12, the MSSS invited people who have been doubly vaccinated and who have been infected with COVID-19 to receive their third dose as soon as they recover. The government has already announced that three doses of vaccine will “soon” be required for the vaccine passport to be valid, without however specifying the date on which this measure will come into force.
Until now, the recommendation was to wait three months, or at least eight weeks, before getting vaccinated after an infection. The new instruction simplifies the message concerning eligibility for the booster dose: if the last dose dates back more than three months, it is time to receive a new one, regardless of whether you have suffered from the disease. Especially since with the few tests available in recent times, it is often difficult to confirm a COVID-19 infection…
The same message is being broadcast in other provinces. In Ontario, eligibility for the booster dose does not take infection into account. In British Columbia, you are asked to wait 10 days after the onset of symptoms before receiving the booster dose.
Government recommendations change, but the analysis of the Dr Gaston De Serres, medical adviser at the National Institute of Public Health of Quebec, remains the same. “When you’ve just had an Omicron infection, you’re not at risk of getting it the following week,” he says. In fact, the Quebec Committee on Immunization has not changed its recommendation on a minimum interval of eight weeks between an infection and a booster dose.
This recommendation is based on the fact that an infection already raises the level of antibodies, and that in this situation, a short-term dose of vaccine is of little use. Can a booster dose immediately after an infection lead to an increased risk of side effects? “We have little data on it,” says the Dr From Serres. “Generally, someone who has had an infection will have more side effects when they receive a dose of vaccine. But it’s unclear whether there’s a big difference if he receives that dose four or eight weeks after infection. »