Controversy over hypothetical third dose of COVID-19 vaccine

Never two without three? The hypothesis that a third dose will become necessary for all people vaccinated against COVID-19 is controversial. World health authorities think it’s too early to make a decision, but pharmacists say scientific evidence supports its importance.

The US-German alliance Pfizer-BioNTech released “encouraging results” from a third dose trial in early July to improve the effectiveness of its vaccine. “Based on current evidence, it is likely that the third dose will be required within 6 to 12 months of full vaccination,” she says, planning to seek approval for the third dose in the United States. USA and Europe in particular.

US health officials have reacted cautiously, stating that “fully immunized Americans do not need revaccinations at this time,” but they say they are prepared to “administer booster doses if and when science shows they are needed.”

The demonstration of the need for a third dose “was absolutely not done,” says Dr Gaston De Serres, chief physician of the Immunization Research Group at the National Institute of Public Health of Quebec. Two doses are sufficient even against the currently discovered variants.

The potential third dose would target people with weakened immune systems, such as those “on immunosuppressants, on dialysis, who have significant kidney failure, kidney, heart, liver and bone marrow transplants,” he says. because they are less responsive to the mechanisms of the vaccine.

Before the advent of COVID-19, “there was always a question mark” about the effectiveness of vaccines for these “subgroups,” adds Dr. De Serres. But for a year and a half, vaccine science has thrived, and research is underway “across the world” to understand the impact of this third dose on these vulnerable patients.

However, countries such as Israel and France did not wait for the conclusions of these studies to begin administering a third dose to some of their populations.

Ethical issue

According to the World Health Organization, unequal access to vaccines already constitutes “flagrant health inequities”. Therefore, the introduction of the third dose will not significantly exacerbate this ethical problem.

So far, two doses of the vaccine protect 90% to 95% of hospital admissions, and studies in Quebec among healthcare professionals show that immunization is unabated after at least 4 months.

However, “immunity does not diminish against what we are vaccinated against, but what circulates is different from what we were vaccinated against,” emphasizes Dr. De Serres. In the case of a vaccine-resistant variant that we “measure in the coming months that this efficacy falls from 90% to, say, 75%, then of course the incentive to give a third dose will be furious.”

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