Evidence of declining efficacy of COVID-19 vaccines is mounting. Even though protection against infections and hospitalizations remains high, more and more governments are opening the door to a booster dose.
Quebec has recommended since last week a booster dose for all people over 70 years of age and those who have received two doses of the AstraZeneca vaccine. The United States and France have done the same recently. Some countries like Israel already vaccinate their entire population with this vaccine at a reduced dose.
Analysis of three studies (done in Sweden, UK and Canada) indicates that immunity wanes after about six months. Remember that vaccination did not start until December 2020, hence the limits of the data.
“The decline in vaccine effectiveness is not surprising. But we didn’t know how long this high immunity would last, ”notes Dr. Jörg Hermann Fritz, of the Department of Microbiology at McGill University.
This decline is mainly seen in the vaccine’s effectiveness in preventing infections. Vaccination remains very effective in protecting against severe forms of COVID-19.
The third dose may sooner or later be recommended for everyone, says Dr Fritz. “Canada in general and Quebec in particular should not wait too long before distributing third doses to the entire population,” he adds.
The side effects of this third dose are similar to those of the second, with perhaps a decrease in their intensity, according to the most recent studies.
Towards a fourth dose?
The decline in vaccine effectiveness suggests that the third dose may one day also become less effective. As for a potential fourth dose, the microbiologist remains cautious. “Right now it’s really hard to say. It will also depend on the evolution of the pandemic. ”
It is above all the appearance of a new generation of vaccines with lasting effects that could change the situation, according to him.
“Most of the current vaccines only target the S protein of the virus. This is indeed crucial and important, but there are other proteins in the virus which can be targeted by the immune system and which can help to prolong the effects of the vaccine, such as the M protein or the N protein ”, explains Dr Jörg Hermann Fritz. “But you have to be vaccinated the first time, first and foremost.”
This text is taken from our newsletter “The Coronavirus Mail” of November 15, 2021. To subscribe, click here.